Dissertations / Theses: 'Merluccius merlucciu'

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CANDELMA, MICHELA. "Study of reproductive biology of European hake (Merluccius merluccius) in Adriatic Sea." Doctoral thesis, Università Politecnica delle Marche, 2017. http://hdl.handle.net/11566/245266.

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Lo scopo del lavoro è stato quello di valutare lo stato attuale dello stock di nasello (Merluccius merluccius, L. 1758) nel mare Adriatico e, più in generale, incrementare la conoscenza sulla biologia riproduttiva di questa specie di importanza commerciale. Per valutare il ciclo riproduttivo, è stato valutato l'andamento degli indici morfometrici per tre anni, il fattore di condizione di Le Cren (Kn), l'indice hepatosomatico (HSI) e l'indice gonadosomatico (GSI). Inoltre, è stata valutata la taglia dei pesci alla prima maturità sia per i maschi che per le femmine. Per la prima volta in Adriatico, è stata calcolata la fecondità, stimata in fecondità di lotto e fecondità relativa, che ha mostrato valori più bassi rispetto ad altre aree del Mediterraneo e Atlantico. Oltre all'analisi macroscopica, è stata eseguita anche l'analisi istologica delle ovaie e testicoli per convalidare la scala macroscopica utilizzata. Infine, per completare lo scenario della fisiologia della riproduzione di questa importante specie commerciale, sono stati sequenziati e caratterizzati gli ormoni gonadotropici (follicle-stimulating hormone, fsh, e luteinizing hormone, lh) e i loro recettori recettori. Nelle femmine, è stata misurata l'espressione di mRNA delle gonadotropine nel cervello e dei recettori negli oociti a differenti classi di oociti, durante il ciclo naturale di riproduzione. Per le gonadotropine, è stato studiata anche la loro localizzazione molecolare nella ghiandola pituitaria delle femmine. Infine, sono stati eseguiti studi tossicologici, attraverso l'analisi dell'espressione molecolare dei geni che indicano una contaminazione da distruttori endocrini, quali vitellogenina a e b e il recettore alpha degli estrogeni nel fegato dei maschi. Tutte le analisi effettuate in questo progetto sono risultate essenziali per prevenire il collasso di questa specie sovrasfruttata. The aim of work was to assess the current state of the stock of European hake (Merluccius merluccius, L. 1758) in Adriatic Sea and overall, to increase the knowledge about its reproductive biology. To evaluate the reproductive cycle, the trend of morphometric indices, Le Cren’s condition factor (Kn), hepatosomatic index (HSI) and gonadosomatic index (GSI) were calculated for three years and the size at first maturity was evaluated in male and female specimens. Furthermore, for the first time in Adriatic Sea, the fecundity, estimated as batch and relative fecundity, were obtained, showing lower values than other Mediterranean and Atlantic areas. In addition to macroscopic analysis, also the histological analysis of the ovaries and testis were performed to validate the used macroscopic scale. Finally, to complete the scenario of the reproductive physiology of this relevant commercial species, the gonadotropin hormones (follicle-stimulating hormone, fsh and luteinizing hormone, lh) and their relative receptors were sequenced, characterized. The mRNA expression of gonadotropins and the receptors was measured in brain and in oocyte, respectively, at different maturity stages of the female specimens during natural reproductive cycle. For the gonadotropins, also their molecular localization was investigated in pituitary gland. Finally, toxicological studies were performed through the analysis of molecular expression of the toxicologically relevant genes (vitellogenin a and b and alpha estrogen receptor), involved in endocrine disruptor metabolism, in male liver, evidencing the contamination in water. All analysis performed in this project are essential to prevent the collapse of overfished species and they should be included in the annual monitoring programs.

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Esposito, Viviana. "Abitudini alimentari di Merluccius merluccius in Alto-Medio Adriatico." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9545/.

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Lo studio delle relazioni trofiche del nasello tramite analisi del contenuto stomacale è particolarmente importante per la gestione della pesca sia di questa specie che delle specie appartenenti alla sua alimentazione. Lo scopo della tesi è stato quello di esaminare l’alimentazione di questa specie utilizzando 200 campioni di nasello provenienti dalla Campagna Medits 2014, e confrontare la metodologia morfologica utilizzata con quella molecolare, determinando i vantaggi di ognuna ed i possibili limiti. La campagna di strascico è stata sviluppata secondo uno schema random stratificato in relazione alla profondità e all’interno di ciascun strato. Lo sbarcato è stato preventivamente sottoposto ad analisi biometriche registrando lunghezza totale, peso, sesso e maturità sessuale di ogni singolo individuo; successivamente sono stati conservati in etanolo gli stomaci prelevati dai 200 naselli scelti per classe di taglia. Sono state riconosciute le prede dei campioni di nasello sia analizzandole qualitativamente (al livello tassonomico più basso possibile), che quantitativamente, considerando alcuni degli indici maggiormente utilizzati. È stato poi calcolato l’indice trofico del nasello e sono stati infine confrontati i risultati con quelli delle analisi molecolari evidenziando le prede non riconosciute e gli errori di identificazione. La metodologia morfologica ha sottolineato che l’alimentazione del nasello dipende fortemente dalla taglia del predatore e dal loro grado di maturità sessuale, ma non varia significativamente in base al sesso. Ha infatti evidenziato una taglia del nasello, corrispondente alla taglia di prima maturità sessuale, in cui la specie cambia gradualmente la sua alimentazione, passando da piccoli crostacei a pesci di grandezza sempre maggiore. Risulta essere un forte predatore specializzato, ma che al tempo stesso risulta essere una specie opportunista, scegliendo il proprio cibo da ciò che ha a disposizione. Il confronto con l’analisi molecolare è stato utile per descrivere i pro e i contro di ciascuna metodologia, dimostrando che è necessario sfruttarle entrambe per avere risultati efficaci e completi dell’alimentazione di una specie.

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Becker, Inga Isabel. "Biochemical and mitochondrial population studies of southern African hake, Merluccius capensis and Merluccius paradoxus." Thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/22639.

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Swanepoel, Hanita. "Profiling and modelling of triglycerides and volatile compounds in SA hake (merluccius capensis and merluccius paradoxus)." Thesis, Bloemfontein : Central University of Technology, Free State, 2011. http://hdl.handle.net/11462/156.

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Thesis (D. Tech. Environmental health) -- Central University of technology, Free State, 2011 Apart from being the primary food source of many cultures around the world, fish contains notable amounts of essential fatty acids that are required by the human body, thus making fish a vital part of the human diet. In South Africa Cape hake is a well-known and highly consumed local fish species, which is transported from coastal areas countrywide where the fresh fish are displayed on ice in various retail stores. Fish is known to be highly susceptible to spoilage and, as a result, the maintenance of the cold-chain in related products is of particular importance. Additionally, recent trends showing a decline in natural fish resources have instigated growing concerns about the sustainability and optimal utilisation of fish as a food source. Against this backdrop, this study aimed at determining the influence of storage parameters on selected triglycerides and their possible metabolic pathways. Also applying prediction modelling of fatty acids and volatiles as instruments to assess exposure of Cape hake fillets to excessive microbial contamination and, in effect, be indicative of the environmental parameters (for example temperature) that may influence such contamination. Randomly selected juvenile hakes were filleted and stored under various simulated retail storage conditions, under either controlled or uncontrolled environmental conditions. For each hake filleted, one fillet was inoculated with an increased load of autochthonous microbiota, and the corresponding fillet was kept at similar temperature conditions. All fillets were monitored over a ten day period, during which fatty acid and volatile samples were collected and analysed. From the resulting triglycerides a selection of fatty acids were profiled and their possible metabolic pathways investigated. Fish maturity, the distribution of the fatty acids and the implication thereof in the nutritional value were also assessed. Conventional chemometric methods utilising mathematical expressions were subsequently utilised in order to predict contamination and whether the cold chain was sustained, while an artificial neural network (ANNs) were designed to predict excessive microbial contamination in the fillets. The results showed that the nutritional value of fish differs notably with its maturity and size. Mathematical equations were furthermore found to be effective assessment instruments to indicate the percentage differences in storage temperature, as well as consequent microbial influences. Thus, this approach may introduce mathematical prediction modelling as a promising mechanism to assess Cape hake spoilage. An artificial neural network (ANN) was successfully designed, that succeeded in distinguishing between Cape hake fillets displayed and stored on ice that have been exposed to excessive contamination and those that have not been exposed. In the latter case, the selected variable was a fatty acid, hexadecanoic acid, used as biochemical indicator. This modulating approach may provide a platform for future shelf-life studies on related muscle tissue. Ultimately, the study endeavoured to add to the body of knowledge regarding the biochemical and microbiological changes related to Cape hake storage, the prediction thereof via contemporary methods and contributing to the safety and effective utilization of this unique and declining South African nutritional resource.

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Bodiguel, Xavier. "Caractérisation et modélisation des processus de bioaccumulation des PCB chez le merlu (Merluccius merluccius) du golfe du Lion." Montpellier 1, 2008. http://www.theses.fr/2008MON13520.

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La compréhension des mécanismes de bioaccumulation des contaminants organiques persistants (POP) est un enjeu majeur pour l’évaluation des risques environnementaux. Lors de ce travail, le devenir d’une famille de contaminants modèles, les polychlorobiphényles (PCB), a été étudié chez une espèce de rang trophique élevé du golfe du Lion, le merlu Européen (Merluccius merluccius). Des concentrations élevées en PCB ont été mesurées dans les merlus de ce secteur en comparaison à celles rencontrées dans la population du golfe de Gascogne. La mise en évidence d’une bioamplification des PCB le long de son réseau trophique, depuis le phytoplancton marin, suggère une influence importante de l’alimentation sur les niveaux de contamination. Le rôle d’autres processus biologiques a également été appréhendé afin de comprendre la forte variabilité des niveaux observés. Ainsi, la croissance, le sexe, mais également le degré de maturité sexuel apparaissent comme des facteurs explicatifs majeurs des concentrations en PCB mesurées dans les poissons. Un modèle de bioaccumulation des PCB chez le merlu, basé sur la théorie de Budget d’Energie Dynamique (DEB), a été développé. Il s’agit d’une approche basée sur le couplage d’un modèle bioénergétique, reproduisant les principales fonctions physiologiques de l’organisme (nutrition, croissance et reproduction), avec un modèle de cinétique des contaminants. La croissance et l’évolution des niveaux de contamination de plusieurs congénères de PCB au cours de la vie des merlus mâles et femelles est simulée de manière satisfaisante, tant dans le golfe de Gascogne que dans le golfe du Lion, validant ainsi les processus pris en compte. Cette approche combinée de modélisation apparaît tout à fait adaptée à l’étude du devenir des contaminants chez les poissons, et ouvre la voie à une compréhension réaliste de leurs effets sur les grandes fonctions biologiques de ces organismes Understanding bioaccumulation mechanisms of persistent organic pollutants (POPs) is a major issue for environmental risk assessment. In this work, polychlorinated biphenyls (PCBs), a model contaminant family, has been studied in the European hake (Merluccius merluccius), a high trophic level species from the Gulf of Lions. High concentrations of PCBs were measured in hake from this area compared to those encountered in the population of the Bay of Biscay. PCB biomagnification was highlighted along its food web from marine phytoplankton, suggesting a strong influence of diet on contamination levels. The role of other biological processes was also apprehended in order to understand the high variability of observed levels. Thus, growth, sex, and also the degree of sexual maturity appear as major factors explaining the measured concentrations in fish. A PCB bioaccumulation model in the hake, based on the Dynamic Energy Budget theory (DEB), was developed. This approach is based on a bioenergetic model, reproducing the main physiological functions of an organism (feeding, growth and reproduction), coupled with a kinetic model of contaminants. The growth and evolution of contamination levels of several PCB congeners during the life of male and female hakes is satisfactorily simulated, both in the Gulf of Lions and in the Bay of Biscay, validating the processes taken into account. This combined modelling approach appears well adapted to study the fate of contaminants in fish, and paves the way for a realistic understanding of their effects on major biological functions of fish

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Testi, Silvia <1967&gt. "Caratteristiche merceologiche, nutrizionali, sensoriali e di freschezza di Nasello (Merluccius merluccius), Lanzardo (Scomber japonicus) e Suro (Trachurus trachurus)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1060/1/Tesi_Testi_Silvia.pdf.

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Three finfish species frequently caught in the waters of the Gulf of Manfredonia (Apulia, Italy) were studied in order to know how the flesh composition (proximate, fatty acid, macro- and micro- element contents) could be affected by the season effect. The species we examined were European hake (Merluccius merluccius), chub mackerel (Scomber japonicus) and horse mackerel (Trachurus trachurus), which were analysed at the raw state in three catch season and after cooking in two catch season. More precisely, European hake and chub mackerel caught during winter, summer and fall were analysed at the raw state. The composition of the flesh of grilled European hake and chub mackerel was study on fish caught in winter and fall. Horse mackerel of summer and winter catches were analysed both at the raw and grilled state. Furthermore, an overall sensory profile was outlined for each species in two catch season and the relevant spider web diagrams compared. On the whole, two hundred and eighty fish were analysed during this research project in order to obtain a nutritional profile of the three species. One hundred and fifty was the overall number of specimens used to create complete sensory profiles and compare them among the species. The three finfish species proved to be quite interesting for their proximate, fatty acids, macro- and micro-element contents. Nutritional and sensory changes occurred as seasons elapsed for chub and horse mackerel only. A high variability of flesh composition seemed to characterise these two species. European hake confirmed its mild sensory profile and good nutritional characteristics, which were not affected by any season effect.

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Testi, Silvia <1967&gt. "Caratteristiche merceologiche, nutrizionali, sensoriali e di freschezza di Nasello (Merluccius merluccius), Lanzardo (Scomber japonicus) e Suro (Trachurus trachurus)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1060/.

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Three finfish species frequently caught in the waters of the Gulf of Manfredonia (Apulia, Italy) were studied in order to know how the flesh composition (proximate, fatty acid, macro- and micro- element contents) could be affected by the season effect. The species we examined were European hake (Merluccius merluccius), chub mackerel (Scomber japonicus) and horse mackerel (Trachurus trachurus), which were analysed at the raw state in three catch season and after cooking in two catch season. More precisely, European hake and chub mackerel caught during winter, summer and fall were analysed at the raw state. The composition of the flesh of grilled European hake and chub mackerel was study on fish caught in winter and fall. Horse mackerel of summer and winter catches were analysed both at the raw and grilled state. Furthermore, an overall sensory profile was outlined for each species in two catch season and the relevant spider web diagrams compared. On the whole, two hundred and eighty fish were analysed during this research project in order to obtain a nutritional profile of the three species. One hundred and fifty was the overall number of specimens used to create complete sensory profiles and compare them among the species. The three finfish species proved to be quite interesting for their proximate, fatty acids, macro- and micro-element contents. Nutritional and sensory changes occurred as seasons elapsed for chub and horse mackerel only. A high variability of flesh composition seemed to characterise these two species. European hake confirmed its mild sensory profile and good nutritional characteristics, which were not affected by any season effect.

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Angileri, Paolo Maurizio Maria. "Struttura di età di nasello (Merluccius merluccius, Linnaeus, 1758) in alto-medio Adriatico mediante analisi degli otoliti e frequenza di taglia." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8090/.

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The aim of present study is to define the general framework of Merluccius merluccius population structure, to estimate the growth rate and to assess the recruitment dynamics of juveniles from Northern and Central Adriatic, through otoliths analysis. The otoliths of hake specimens collected during the MedITS trawl survey in the 2012 in GSA 17, were cleaned and 102 otoliths out of 506 were embedded, sectioned, grindined and polished to obtain frontal and sagittal sections. The whole sample were analysed under stereomicroscope and optical microscope, with camera and connected to PC provided of an image analyses program. The frequency analysis of size classes and age revealed that the species is dominated by hake with >200mm TL and > one year old. The fish average size of M. merluccius at the end of the first year of life is about 199 mm TL. Allometrics analyses between fish TL and Feret (major axis), MiniFeret (minor axis), Area, Perimeter, showed a direct proportionality among lengths. Among the 88 otoliths sections analysed, the number of daily increments read ranged from 86 to 206, within 55 and 175mm TL range. The age estimate ranged from about 2-3 to 9 months and the growth rate from 20.99 to 27.15mm TL. The hatch-date distribution, obtained by back calculation, showed that the hatching occurs in November-March. In conclusion, strong preventive measures are needed for hake adults because the success of this species seems to be linked to deep water ecosystem protection where big spawners dwell.

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Lundy, Caroline. "Genetic structure of demersal fish populations in oceanic environments : implications for management of European hake (Merluccius merluccius), a commercially important species." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323388.

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Millar, Dinah Lynn. "Distribution and abundance of Cape hakes (Merluccius capensis and Merluccius paradoxus) in relation to environmental variation in the Southern Benguela system." Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/10666.

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Bibliography: leaves 111-128. Standard Geographical Information Systems (GIS) techniques and Generalized Additive Models (GAM), nonparametric regressions without the assumptions of normality or linearity of traditional regression methods, were used to test the hypothesis that trends in hake (M. paradoxus and M. capensis) distribution and abundance are related to ocean environmental conditions (including bottom temperature, bottom oxygen concentration, sea surface temperature and sea surface minus bottom temperature, as a measure of stratification or mixing) and location (including longitude, latitude and bottom depth). Hake and physical data, from seventeen biomass surveys undertaken by Marine and Coastal Managment between 1984 and 1997 in the southern Benguela ecostystem, were used to test these relationships.

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Bastide-Guillaume, Christine. "Etude écophysiologique de certaines parasitoses chez trois gadiformes du Golfe du Lion Merluccius merluccius (Linnaeus, 1758), Trisopterus minutus capelanus (Lacepede, 1800)." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37595735v.

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Jolivet, Aurélie. "Compréhension des mécanismes de biominéralisation : quantification spatialisée des fractions minérale et organique et influence de facteurs environnementaux." Brest, 2009. http://www.theses.fr/2009BRES2055.

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Malgré un grand nombre d’études relatives à l’utilisation des otolithes, les connaissances sur les mécanismes de formation de l’otolithe et leur modulation par les facteurs environnementaux et physiologiques restent parcellaires. En particulier, la caractérisation des fractions minérale et organique des structures de I’otolithe et l’influence de leurs propriétés qualitatives et quantitatives sur l’opacité restent peu documentées, Pourtant ces informations sont d’importance en vue d’une calibration robuste de l’archive « otolithe ». Le premier axe de recherche s’est concentré sur l’opacité et les effets de la température, la croissance et du métabolisme à partir d’expérimentation en milieu contrôlé. L’opacité a ainsi été définie comme une fonction de deux contributions énergétiques: l’une relative à la croissance somatique et l’autre indépendante de la croissance somatique et associée à des mécanismes de maintenance. Le second axe de recherche s’est focalisé sur l’analyse des propriétés physico-chimiques des structures de l’otolithe. Le développement d’une approche de micro-spectrométrie Raman, non destructive, nous a permis de discriminer de manière quantitative des signatures organique et minérale à une très haute résolution. La caractérisation de micro et macrostructures a permis la construction d’un modèle de prédiction de l’opacité en fonction des signatures de ces deux fractions. Si la relation entre facteurs modulant la biominéralisation et caractéristiques physicochimiques des structures reste à établir, les résultats obtenus dans cette thèse ouvrent de pistes prometteuses pour une meilleure compréhension des mécanismes de formation de l’otolithe Despite numerous applications on the use of otoliths at both population and individual levels, knowledge regarding the mechanisms of the otolith and their variations with environmental and physiological factors has to be improved. In particular, the characterization of mineral and organic fractions of the otolith structures and the influence of their qualitative and quantitative composition on the opacity remain poorly documented. Vet this information is of key interest for the calibration of the archive “otolith” allowing a robust analysis of information. The first issue of this study focused on the analysis of the opacity and the effects of temperature, growth and metabolism through experiments in controlled conditions. Results led to the modelling of opacity as a function of two energetic contributions: one related to somatic growth and the other independent of somatic growth and associated to maintenance mechanisms. The second issue dealt with the physico-chemical characterization of otolith structures. The development of an approach based on micro-spectrometry Raman, non-destructive, has allowed to quantitatively discriminating organic and mineral signatures at very high resolution. It has led to the characterization of microstructures (L and D zones) and macrostructures (translucent and opaque zones) led to the development of a predictive model of opacity from the signatures of these two fractions. The relationship between the environmental and metabolic factors and the chemical composition of structural features has still to be established but our results promising perspectives for a better understanding of the mechanisms of otolith biomineralisation

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Drouineau, Hilaire. "Développement et ajustement d’un modèle de dynamique des populations structuré en longueur et spatialisé appliqué au stock Nord de merlu (Merluccius merluccius)." Rennes, Agrocampus Ouest, 2008. http://www.theses.fr/2008NSARH073.

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Bien que le merlu de l’Atlantique nord-est ait été largement étudié, certaines caractéristiques de sa biologie sont encore assez mal connues. C’est en particulier le cas de ses migrations saisonnières et de sa croissance, dont une campagne récente de marquage montre qu’elle était probablement largement sous-estimée. Ces incertitudes ont plusieurs conséquences tant sur la qualité des diagnostics établis à l’aide des modèles de dynamique des populations usuels, que sur la gestion en limitant notamment les possibilités d’évaluatin de mesures de gestions spatialisées. Pour améliorer l’estimation des paramètres de ces processus, nous avons développé un modèle de dynamique de population intégré spatialisé et structuré en longueur en reposant sur un modèle d’états décrivant la dynamique de la population et de l’activité de pêche, et sur un modèle décrivant les processus d’observation, permettant l’écriture d’une fonction de vraisemblance. Une revue bibliographique des modèles structurés en longueur existants a mis en évidence le rôle clé de la modélisation du processus de croissance dans ce type de modèles. Pour s’assurer de la robustesse des hypothèses du modèle liées à la discrétisation de ce processus continu et à la variabilité individuelle de croissance, nous avons réalisé une analyse de sensibilité du modèle de croissance. Cette méthode d’exploration numérique du modèle repose sur (i) le développement de plans d’expériences et (ii) l’ajustement de modèles statistiques aux sorties du modèle pour quantifier l’impact de ces hypothèses. Cette démarche générique est transportable à toute analyse de sensibilité d’un modèle discret décrivant un processus continu.

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Sutton, Glen Robert. "Exploitation patterns of the multi species/gear hake (Merluccius capensis and paradoxus) fishery on South Africa's southeast coast." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005124.

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The motivation for this study was to examine the exploitation patterns of the M. capensis and M. paradoxus hake fisheries on the Southeast Coast, and determine the size and species of hake caught in each of the hand-line, long-line, and trawl methods. The handline hake fishery has increased substantially over the last several years and concerns are beginning to emerge about the impact this will have on the inshore resource collected on the South Coast between August 1998 and July 1999 was used to describe the hand-line method and estimate annual landings. Data on the size and species in longline catches of hake caught during 1997 were already available for this study. Size distributions in trawl catches were determined from commercial category landing data reported by catch weight and depth. The species composition in these catches determined by comparison using RV Afrikana survey data collected in the same depth regions. Location plays a significant role in determining the sizes and species of hake caught by each gear. Hand-lines catch smaller sizes on average than do long-lines, inshore trawls target mainly M. capensis while offshore trawls catch both hake species. A substantial amount of the hand-line hake caught on the South Coast is not reported. Examination of the exploitation patterns reveal that intense trawling pressure is directed at the smaller sized M. paradoxus inhabiting the depth region between 160-400-meters. Inshore trawls discard a large amount of small sized M. capensis within the 100-meter isobath. A preliminary stock assessment on the status of each hake species found that M. paradoxus appears to be over-exploited while M. capensis was in better shape. However, length-based pseudo-cohort analysis, used in this assessment, is critically reliant on having length frequency data from a steady state population in equilibrium. This limits the application of this model for management purposes and this finding is purely theoretical at this stage. Results suggest that each hake species is under a different pattern and level of exploitation and the multi-species nature of hake stocks on the South Coast should be considered in developing optimum management policies. Future work should focus on developing appropriate age/length keys so that an age-based VPA, which is more powerful than the length-based approach, can be applied towards stock assessments on the South Coast. Alternatively, length-data covering a longer period should be compiled and the equilibrium assumption further investigated so that the results from length-based models can be used with more confidence.

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Boey, Chee Cheong. "Utilization of Pacific hake (Merluccius productus) in thermally processed products." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24483.

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The potential of Pacific hake (Merluccius productus), which occur in Pacific north east waters, for human consumption is of interest because the biomass of the fish is known to be of significant size. However, this resource has not been fully exploited by the local fishing industry. The presence of Myxosporean parasite spores in the fish muscle is thought to cause a soft cooked fish texture, thus giving rise to problems in processing and affecting the marketability of the fish product. Studies were conducted on the textural properties of Pacific hake from two different fishing areas with different postharvest handling treatments. Fish samples from the Strait of Georgia and from offshore waters west of Vancouver Island were obtained from commercial sources. The west coast offshore hake samples were obtained in frozen form. They were thawed, filleted, vacuum-packed in barrier bags and refrozen for storage at -29°C. Two batches of fish chilled in refrigerated sea water were available from Georgia Strait. One of these batches was frozen immediately when received and subsequently processed similar to the west coast samples, whereas the other batch was chilled in ice for 1-3 days after landing while the fish were progressively processed into fillets for frozen storage at -29°C. The presence and types of species of Myxosporean parasite spores in fish fillets were determined by light and scanning electron microscopy. The fillets were grouped according to the level of infection in terms of the numbers of parasite spores determined by wet mount microscopic examination. The potential of Pacific hake (Merluccius productus), which occur in Pacific north east waters, for human consumption is of interest because the biomass of the fish is known to be of significant size. However, this resource has not been fully exploited by the local fishing industry. The presence of Myxosporean parasite spores in the fish muscle is thought to cause a soft cooked fish texture, thus giving rise to problems in processing and affecting the marketability of the fish product. Studies were conducted on the textural properties of Pacific hake from two different fishing areas with different postharvest handling treatments. Fish samples from the Strait of Georgia and from offshore waters west of Vancouver Island were obtained from commercial sources. The west coast offshore hake samples were obtained in frozen form. They were thawed, filleted, vacuum-packed in barrier bags and refrozen for storage at -29°C. Two batches of fish chilled in refrigerated sea water were available from Georgia Strait. One of these batches was frozen immediately when received and subsequently processed similar to the west coast samples, whereas the other batch was chilled in ice for 1-3 days after landing while the fish were progressively processed into fillets for frozen storage at -29°C. The presence and types of species of Myxosporean parasite spores in fish fillets were determined by light and scanning electron microscopy. The fillets were grouped according to the level of infection in terms of the numbers of parasite spores determined by wet mount microscopic examination. Land and Food Systems, Faculty of Graduate

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Samaranayaka, Anusha Geethangani Perera. "Pacific hake (Merluccius productus) fish protein hydrolysates with antioxidative properties." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/20892.

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Pacific hake (Merluccius productus) is an under-valued fish with high endogenous proteolytic activity due to parasitic infection by Kudoa paniformis. The objective of this research was to produce fish protein hydrolysates (FPH) with antioxidative properties from Pacific hake and to assess their potential to inhibit oxidative processes, in vivo. Proteolytic activity of fish homogenate was optimum at pH 5.25-5.50 and 52-55°C. Significant (p<0.05) correlations were observed among fish mince K. paniformis spore counts, endogenous proteolytic activity, and content of free amino groups during autolysis. Autolysis of Kudoa-infected fish fillet mince (30 x 10⁶ spores/g) for 1 h at 52°C and pH 5.50 produced FPH with high antioxidative capacity in a linoleic acid model system, which was higher (p<0.05) than that of butylated hydroxyanisole and α-tocopherol over prolonged storage (~162 hrs). Trolox equivalent antioxidant capacity and oxygen radical absorbing capacity values of FPH were 262 ±2 and 225 ±17 μmol Trolox equivalents/g freeze-dried sample, respectively. Further, FPH could scavenge 1,1-diphenyl-2-picrylhydrazyl radicals, but iron-chelating ability was very low. When in vitro angiotensin-I-converting enzyme (ACE)-inhibitory potential was quantified to examine potential multifunctional capacity, FPH was shown to be a substrate-type inhibitor of ACE with IC₅₀ of 162 µg peptides/mL. In vitro gastrointestinal (GI)-digestion of FPH increased (P<0.05) antioxidative capacity, while ACE-inhibitory activity remained unchanged. Some peptides from FPH and GI-digested FPH passed through Caco-2 cells, and the permeates showed 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging capacity but not ACE-inhibitory activity. FPH and GI-digested FPH inhibited 2,2′-azobis-(2-amidinopropane) dihydrochloride-induced oxidation in Caco-2 cells at non-cytotoxic concentrations. Both antioxidative and ACE-inhibitory peptides were concentrated in a 1-3 kDa fraction by ultrafiltration, but the peptides having antioxidative capacity differed from those exhibiting ACE-inhibitory activity. Two peptides (PLFQDKLAHAK and AEAQKQLR) were identified and their antioxidative potential, along with three other literature reported antioxidative peptides, were assessed in different in vitro chemical systems; antioxidative capacities depended on peptide sequence, amino acid composition, and the in vitro assay system used. In conclusion, antioxidative FPH from Pacific hake could be a useful functional food ingredient. Further studies are needed to assess prospective antihypertensive effects and to identify antioxidative mechanisms of constituent peptides.

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17

Roelf, Craig Ashley. "Categorisation and chemical composition of Cape hake (Merluccius ssp.) waste." Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/53730.

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Thesis (MScAgric)--University of Stellenbosch, 2004. ENGLISH ABSTRACT: Cape hake (Merluccius capensis and M. paradoxus) is commercially the most important trawl-caught fish off the South African, coastline and due to current intensive fish processing procedures Cape hake contributes the most to the total fishwaste production. Besides its commercial importance fish is also regarded as one of the single most important consumable natural resources, either in the raw or frozen form. Most of South Africa's commercially trawled demersal fish has already been partially cleaned (i.e. headed and gutted) before landing with non-marketable bycatch and hake-waste normally disposed of as discards, resulting in a waste of a potential protein source. This study was thus aimed at fulfilling several objectives namely: observing the current large-scale commercial Cape hake harvesting procedure; constructing prediction models for several morphological parameters (whole hake mass, headed & gutted hake mass, hake head mass, hake head length, hake head breadth and hake head height) of Cape hake (Merluccius ssp.), using whole hake length as the independent variable; and determining the chemical composition (moisture, protein, fat, ash, macro and trace elements) of several hake head sections (clean head, neck flesh, tongue, tongue cartilage, jaw, gills, heart, intestines, gut, kidney, kidney & kidney bone and gut & gall); determining the effect that storage has on the fatty acid profile of both the clean head and neck flesh sections. The results obtained would supply necessary data required for techno-economic investigations in the use of hake heads. For each of the six prediction models constructed, there was an increase in the variance of the data points of categories 3 (64-80 cm) and 4 (>80 cm) as opposed to categories 1 (30-46 cm) and 2 (47-63 cm). This could be attributed to a smaller sample set for both categories 3 and 4 or due to an expected increase in the variance when investigating larger biological samples. There was also a clustering of data in the three areas for each prediction model namely, within category 1 and across categories 2 and 3 and 3 and 4. This emphasised the latitudinal stratification of the Cape hake population by age, hence their stratification by size. The prediction models constructed for both boat trips 2 and 3 differed significantly (p<0.01) from that of boat trip 1, with the exception of the hake head length (cm) prediction model. The constructed prediction models, for each of the three respective boat trips, showed good predictive abilities as was indicated by the low Mean Square Error (MSE) values for the test sets, and high Pearson's correlation coefficient (r) values. These prediction models can be used in the fishing industry with confidence for Cape hake within the time frame each respective boat trip was carried out. The neck flesh could be regarded as the most important concerning chemical composition whereas the jaw could be seen as the most important when one considers mineral content. This therefore means that the jaw section, once appropriately processed is a potential Ca, Na and Fe source for supplementing diets of people suffering from a Ca, Na or Fe deficient diet. With regard to chemical status the neck flesh section is seen as a good potential source of both protein and fat, which could be attributed to the fact that hake muscle constitutes a major portion of this section. This section could thus be used to supplement the protein and fat of an existing food product, which is protein and fat deficient for people suffering from a protein and fat deficient diet. Similarly, a market could be created for the production of an economical food product with the neck flesh section being the main ingredient. Once this have been accomplished, fishing vessels may be persuaded to retain their Cape hake fish-waste for further processing due to the value of the prepared food products and thereby maintain profitability while abiding to governmental law. In conclusion non-government scientists should have more input in the decision-making process concerning matters affecting South Africa's marine biodiversity in order for future key policy and legislation drafts to be effective. Improvement of current fish preservation techniques and the known chemical composition of currently discarded material will result in informed decisions of future matters concerning its disposal. AFRIKAANSE OPSOMMING: Kaapse stokvis (Merluccius capensis en M. paradoxus) is kommersieel Suid-Afrika se belangrikste vis spesie. Aangesien die Suid-Afrikaanse visprosesseringsbedryf baie intensief is, dra die Kaapse stokvis verwerkingsindustrie die grootste gedeelte by tot die totale visafval produksie. Die meeste van Suid-Afrika se visvangste word gedeeltelik skoongemaak voor landing terwyl nie-kommersiële byvangste en visafval gewoonlik oorboord gegooi word tydens die vangproses. Dit lei tot die vermorsing van 'n potensïele proteïen bron. Hierdie studie was dus gemik om: die huidige grootskaalse kommersiële Kaapse stokvis visvangsproses waar te neem; voorspellingsmodelle vir verskeie morfologiese parameters (heel vis massa, vis massa sonder kop en binnedele, stokvis kop massa, stokvis kop lengte, stokvis kop breedte en stokvis kop hoogte) vir Kaapse stokvis (Merluccius ssp.) te ontwikkel deur die hele lengte van die vis te gebruik as die onafhanklike veranderlike; die chemiese samestelling (vog, proteïen, vet, as, makro en spoor elemente) van verskillende dele van die viskop (skoonkop, nekweefsel, tong, tong kraakbeen, kaak, kiewe, hart, ingewand, derm, nier, nier & nierbeen en derm & gal); sowel as die effek van opberging op die vetsuurprofiel van beide die skoonkop en nekweefsel dele van die Kaapse stokvis kop. Hierdie resultate sal dan gebruik word vir die tegnies-ekonomies ondersoek in die gebruik van Kaapse stokvis koppe. Vir elk van die ses voorspellingsmodelle ontwikkel, was daar 'n vermeerdering in die variansie van die datapunte vir kategorieë 3 (64-80 cm) en 4 (>80 cm) teenoor kategorieë 1 (30-46 cm) en 2 (47-63 cm). Dit kan moontlik wees as gevolg van die kleiner monster trekking vir beide kategorieë 3 en 4 of as gevolg van verwagte toename in variansie wanneer groter biologiese monsters ondersoek word. Daar was ook 'n groepering van data in drie plekke vir elke voorspellingsmodel naamlik; binne in kategorieë 1 en oor kategorieë 2 en 3 en 3 en 4. Dit beklemtoon die geografiese breedte van die Kaapse stokvis populasie op grond van ouderdom, en dus die geografiese breedte op grond van grootte. Die voorspellingsmodelle ontwikkel vir beide die tweede en derde bootvangs het betekenisvol verskil (p<0.01) van die eerste bootvangs, behalwe die vir die stokvis kop lengte (cm) voorspellingsmodel. Die voorspellingsmodelle vir elk van die bootvangste het goeie voorspellingsvermoë getoon wat bewys is deur die lae Gemiddelde Kwadraat Fout waardes vir toetsgroepe en hoë Pearson's korrelasie koeffisiënt (r) waardes. Hierdie voorspellingsmodelle wat ontwikkel is, kan dus met vertroue in die Kaapse stokvis visvangsbedryf gebruik word mits dit ooreenstem met die periode waarin elke bootvangs uitgevoer was. Die nekweefsel gedeelte is die mees belangrikste met betrekking tot chemiese samestelling en die kaak die belangrikste in terme van minerale samestelling van die verskeie viskop dele. Die kaak is dus, as dit voldoende geprosesseer word, 'n goeie potensïele bron van Ca, Na en Fe en kan dus gebruik word om die dieet van mense wat 'n gebrek het aan hierdie minerale aan te vul. Met betrekking tot die chemiese samestelling van die nekweefsel gedeelte kan dit beskou word as 'n goeie potensiële bron van beide proteïen en vet, wat toegeskryf kan word aan die feit dat spierweefsel 'n groot deel uitmaak van hierdie viskop gedeelte. Hierdie viskop gedeelte sal dus uitstekend wees om die proteïen- en vetinhoud van 'n voedselproduk wat van nature 'n lae proteïen- en vetinhoud het te verhoog en hierdie produk sou dan geteiken word op daardie gedeelte van die gemeenskap wat 'n proteïen en vet tekort in hul dieet het. As dit eers alles in plek is, dan sal die visvangs bedryf hul Kaapse stokvis afval behou vir verdere prosessering deurdat dit gebruik word om die voedingsinhoud van bestaande voedsel soorte sal verbeter en terselfdertyd sal hulle aan wetgewing voldoen. Gevolglik sal nie-regerings navorsers meer betrokke moet wees by die besluitnemingsproses met betrekking tot sake wat die Suid-Afrikaanse mariene lewe affekteer en wat toekomstige wetgewing meer effektief sal maak. Die verbetering van huidige vis preserveringstegnieke gepaardgaande met die kennis van die chemiese samestelling van die Kaapse stokvis koppe sal lei na beter toekomstige besluite oor die afset daarvan.

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18

Wilhelm, Margit Renate. "Growth and otolith zone formation of Namibian hake, merluccius capensis." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/10785.

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Includes bibliographical references. Life history traits and tactics of commercially important Namibian shallow-water hake, Merluccius capensis, were investigated in relation to their environment. A time series of length-frequency distributions (LFDs) from otoliths collected from fur seal scat samples was used to identify cohorts and calculate the approximate hatchdates and growth rates of young M. capensis from 1994 to 2009. Monthly otolith samples of five of these cohorts (1996, 1998, 2002, 2005 and 2006) were used to evaluate the translucent zone periodicity over the first 21 months of their life. Additionally, LFDs from research surveys and commercial samples were used to calculate growth rates for M. capensis up to 65 cm total length (TL), and to further validate the translucent zone formation of three of the five cohorts (1996, 1998 and 2002) on fish up to 3.5 years old.

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19

Milano, Ilaria <1983&gt. "Novel tools for conservation genetics in marine fish: population structure and evolution of the European hake (Merluccius merluccius) inferred by SNP variation and applications to traceability." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4728/1/Milano_Ilaria_tesi.pdf.

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The research presented in my PhD thesis is part of a wider European project, FishPopTrace, focused on traceability of fish populations and products. My work was aimed at developing and analyzing novel genetic tools for a widely distributed marine fish species, the European hake (Merluccius merluccius), in order to investigate population genetic structure and explore potential applications to traceability scenarios. A total of 395 SNPs (Single Nucleotide Polymorphisms) were discovered from a massive collection of Expressed Sequence Tags, obtained by high-throughput sequencing, and validated on 19 geographic samples from Atlantic and Mediterranean. Genome-scan approaches were applied to identify polymorphisms on genes potentially under divergent selection (outlier SNPs), showing higher genetic differentiation among populations respect to the average observed across loci. Comparative analysis on population structure were carried out on putative neutral and outlier loci at wide (Atlantic and Mediterranean samples) and regional (samples within each basin) spatial scales, to disentangle the effects of demographic and adaptive evolutionary forces on European hake populations genetic structure. Results demonstrated the potential of outlier loci to unveil fine scale genetic structure, possibly identifying locally adapted populations, despite the weak signal showed from putative neutral SNPs. The application of outlier SNPs within the framework of fishery resources management was also explored. A minimum panel of SNP markers showing maximum discriminatory power was selected and applied to a traceability scenario aiming at identifying the basin (and hence the stock) of origin, Atlantic or Mediterranean, of individual fish. This case study illustrates how molecular analytical technologies have operational potential in real-world contexts, and more specifically, potential to support fisheries control and enforcement and fish and fish product traceability.

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20

Milano, Ilaria <1983&gt. "Novel tools for conservation genetics in marine fish: population structure and evolution of the European hake (Merluccius merluccius) inferred by SNP variation and applications to traceability." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4728/.

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The research presented in my PhD thesis is part of a wider European project, FishPopTrace, focused on traceability of fish populations and products. My work was aimed at developing and analyzing novel genetic tools for a widely distributed marine fish species, the European hake (Merluccius merluccius), in order to investigate population genetic structure and explore potential applications to traceability scenarios. A total of 395 SNPs (Single Nucleotide Polymorphisms) were discovered from a massive collection of Expressed Sequence Tags, obtained by high-throughput sequencing, and validated on 19 geographic samples from Atlantic and Mediterranean. Genome-scan approaches were applied to identify polymorphisms on genes potentially under divergent selection (outlier SNPs), showing higher genetic differentiation among populations respect to the average observed across loci. Comparative analysis on population structure were carried out on putative neutral and outlier loci at wide (Atlantic and Mediterranean samples) and regional (samples within each basin) spatial scales, to disentangle the effects of demographic and adaptive evolutionary forces on European hake populations genetic structure. Results demonstrated the potential of outlier loci to unveil fine scale genetic structure, possibly identifying locally adapted populations, despite the weak signal showed from putative neutral SNPs. The application of outlier SNPs within the framework of fishery resources management was also explored. A minimum panel of SNP markers showing maximum discriminatory power was selected and applied to a traceability scenario aiming at identifying the basin (and hence the stock) of origin, Atlantic or Mediterranean, of individual fish. This case study illustrates how molecular analytical technologies have operational potential in real-world contexts, and more specifically, potential to support fisheries control and enforcement and fish and fish product traceability.

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21

Roa-Varon, Adela Y. "Multi-Scale Phylogenomics of Gadiformes With Emphasis on Hakes (Merluccius, Merlucciidae)." W&M ScholarWorks, 2018. https://scholarworks.wm.edu/etd/1550153685.

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Gadiformes include some of the most important commercially harvested fishes in the world (e.g. cods, hakes, and grenadiers). Currently, different authors recognize anywhere between 11 and 14 families, approximately 84 genera, and over 600 species. The monophyly of the order has been supported by both morphological and molecular data, yet the relationships among families and subfamilies remain poorly understood and interpreting phylogenetic patterns to date has been difficult. My dissertation research on multi-scale phylogenetics of Gadiformes with emphasis on hakes (Merluccius, Merlucciidae) has three primary objectives: (1) to improve the understanding of the phylogenetic relationships among families of Gadiformes (Teleostei); (2) to analyze the phylogenetic relationships within the family Merlucciidae (Merluccius) and (3) to explore the evolution of the caudal skeleton using molecular, morphological and ecological data. in chapter two, a gene capture approach was used, targeting coding DNA sequences (CDS) from single-copy protein-coding genes to study the higher-level relationships (i.e., above the genus level) of Gadiformes. Matrices of 14,208 loci (~2.8 M bp) were generated from a total of 57 species representing all recognized Gadiformes families and subfamilies. Species tree and concatenated maximum likelihood analyses resolved a highly congruent and well-supported phylogeny at both shallow and deep levels that contributes towards stabilizing higher-level Gadiformes classification. in accordance with these results a revised classification of the group is provided in chapter two. in Chapter three the systematics, evolution, and taxonomy of a particularly problematic family, the hakes (Merluccius, Merlucciidae), using genomic data from 13,771 loci and 74 taxa were reassessed. This study resolved the controversy surrounding the taxonomic extent of Merlucciidae and the phylogenetic placement of the genera historically included within the family, based on complete taxonomic sampling at the family and subfamily levels among gadiforms. Additionally, the phylogenetic analysis confirmed an early separation of two lineages of Merluccius, the Old World and the New World clades. The Old World clade includes five well defined species and the New World clade includes three species and two complexes of species suggesting the presence of only one species in the eastern Pacific, as well as, one species in the Southern Ocean (Patagonia – New Zealand). Chapter four provided for the first time a description of the caudal skeleton for all the families among Gadiformes and explores the character evolution of 11 characters (morphological and ecological) mapped on a taxonomically robust phylogenetic hypothesis proposed in chapter two. The ancestral state reconstruction analyses suggest that the ancestral condition among gadiforms had a caudal fin and a pelagic origin. Its loss arose at least two times within Gadiformes resulting in two main phenotypes - the tailed and the tailless fishes, neither of which form a monophyletic grouping. This study is the most comprehensive phylogenomic study of Gadiformes to date. This dissertation used a novel molecular technique coupled with morphological and ecological data that resulted in a better understanding of the evolution of commercially and ecological valuable fishes, which is necessary for effective fisheries management and the preservation of reproductive and genetic diversity. Further steps, including morphological data of extant and extinct taxa, is essential to fully understand macroevolutionary patterns and processes in phenotypic evolution and lineage diversification of gadiforms.

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22

Vincenzi, Carolina. "Influenze ontogenetiche e ambientali sui fattori di condizione di Merluccius merluccius Linnaeus, 1758 (Pisces: Gadiformes) e Galeus melastomus Rafinesque, 1810 (Pisces: Carcharhiniformes): Implicazioni sulla gestione delle risorse." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8282/.

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In ecologia della pesca, i fattori o indicatori della “condizione” di un organismo forniscono molte informazioni sulle caratteristiche di adattamento dei pesci all’ambiente e sul loro ruolo nell’ecosistema. La “condizione” include molte caratteristiche strutturali ed energetiche che possono variare in funzione dell’ontogenesi, del ciclo riproduttivo, ma anche in funzione delle caratteristiche dell’ambiente, incluso il grado di stress al quale è sottoposta una specie (es. la pressione di pesca). L’obiettivo del presente studio sperimentale è stato valutare eventuali differenze nell’abbondanza, nei parametri di popolazione, nella struttura demografica e negli indicatori di “condizione” di due specie, Merluccius merluccius (Pisces: Gadiformes) e Galeus melastomus (Pisces: Carcharhiniformes), in due diverse aree: Toscana settentrionale e meridionale, differenti per caratteristiche ambientali e pressione di pesca. Nella prima parte dell’analisi, sono stati confrontati gli indici di densità e biomassa, la struttura di taglia delle due popolazioni, su dati estratti dagli archivi storici delle campagne di pesca sperimentale MEDITS dal 1994 al 2013. Nella seconda parte dell’analisi invece, sono stati analizzati 1000 individui provenienti dalla campagna MEDITS 2014, integrati con campioni provenienti dallo sbarcato commerciale per il biennio 2014-2015. Gli individui di M. merluccius sono stati ripartiti in due classi di taglia (I = individui ≤ 18 cm LT; II = individui > 18 cm LT), quelli di G. melastomus in tre classi di taglia (I = individui ≤ 20 cm LT; II = individui 20 cm< x ≤ 35 cm LT; III= individui > 35 cm LT), suddivisi rispettivamente in 50 maschi e 50 femmine, per ogni classe. E’ stato condotto lo studio della crescita relativa attraverso l’analisi della relazione taglia/peso e lo studio della condizione tramite i seguenti indicatori: il fattore K di Fulton, l’indice epatosomatico (HSI) e l’indice gonadosomatico (GSI). I risultati di questa tesi hanno evidenziato differenze nei popolamenti, riconducibili alle diverse condizioni ambientali e alla pressione di pesca, tra le due aree indagate. L’area sud, interessata da un più intenso sforzo di pesca esercitato sui fondali della piattaforma e della scarpata continentale e da una morfologia del fondale differente, mostra una diversità in termini di crescita relativa e stato della “condizione”, che risulta più elevata in entrambe le specie, rispetto all’area settentrionale, caratterizzata invece da uno sforzo di pesca meno intenso, incentrato sull’ampia piattaforma continentale.

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23

Fairweather, Tracey Pamela. "An analysis of the trawl and longline fisheries for Merluccius capensis off the west coast of South Africa." Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1005061.

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The South African hake resource faces divergent fishing pressures and management issues. Although the resource consists of two species, management was simplified because the resource was only subject to trawl effort and because of the similarity in population parameters, single species assessment models could be adopted. The impact of trawling on the stock is considered to be well understood and the resource has shown recovery since exclusion of foreign vessels. The 1990s were punctuated by major political change and the need for transformation has resulted in an expansion of the number of fishing rights holders. Longlining has been reintroduced and there is no clear understanding of how the combined fishing pressures will affect the population structure of either Merluccius capensis or M. paradoxus. Information is vital to successful management. Fisheries are complex and intricate, and at times appear impossible to control or monitor. An integrated information system provides easily understood graphical explanations of complex issues. This thesis assessed the dynamics of the trawl and longline fisheries between 1994 and 1999 using a geographical information system (GIS). The accessability of a GIS incorporates the needs of scientists, managers and fishing communities. The simple GIS developed in this study revealed shifts in effort, facilitated the calculation of spatially precise catches and biomasses and highlighted the inadequacy of current sampling coverage. Trawlers were shown to fish the same areas consistently during the years investigated, with highest fishing intensity and average CPUE achieved at depths between 300 and 500m. Analysis of the longline sector revealed several similarities to the trawl sector, fishing intensity was highest between 301 and 500m, suggesting that both sectors face a "friction of distance" dilemma. The distribution and abundance of hake, in particular the exploitable proportion of the population, was determined by a combination of depth and substrate type. The selectivity patterns of trawlers and longliners were briefly investigated with the results illustrating that gear selectivity of the M. capensis stock was depth dependent. The deeper fishing occurred, the larger the length-at-selection. As a result, the M. capensis parental stock faces unprecedented fishing pressure. In the absence of reliable species-specific catch data, logistic and linear regression models were developed to split the hake catch into its respective species components. Large discrepancies between the predicted M. capensis catch for the two models were noted. Regression estimates constructed at a finer spatial scale may provide a better fit than the current depth logistic employed by Marine and Coastal Management. A first attempt at assessing the M. capensis resource on the West Coast using an age-structured production model was presented. It was found that a lengthy and accurate M. capensis catch series is required before it is possible to successfully model the dynamics of the stock. It is necessary to incorporate finer spatial detail in the collation of catch data and collection of sampling data. It would be unadvisable to assume that the stock is stable or recovering. The implications of a size/sex relationship must be investigated and properly appraised.

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24

Ferraton, Franck. "Ecologie trophique des juvéniles de merlu (Merluccius merluccius) dans le golfe du Lion : implications biologiques de la variabilité spatio-temporelle des ressources alimentaires exploitées dans les zones de nourricerie." Montpellier 2, 2007. http://www.theses.fr/2007MON20223.

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25

Van, der Merwe Marla. "Development of value-added products using the neck flesh of Cape Hake (Merluccius Capensis)." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52765.

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Thesis (MSc Food Sc )--Stellenbosch University, 2002. ENGLISH ABSTRACT: The focus of this study was the development of food products produced from the neck flesh of Cape hake (Merluccius capensis) as a means of adding value to hake heads. The product prototypes that have been developed include curried fish chowder (packaged in stand-up pouches), fish spread (packaged in plastic casings) and Chakalaka hake (packaged in both cans and retortabie pouches). A formula for fish stock, which was used as a base ingredient in the three product prototypes, has also been standardised. Shelf life testing was regarded an essential part of the development processes for the refrigerated product prototypes i.e. the curried fish chowder and the fish spread. Shelf life determinations involved microbiological testing based on set microbiological standards as well as sensory monitoring and pH testing. Proximate chemical- and mineral analyses were performed on freeze-dried samples of the developed product prototypes. The efficiency of the antimicrobial peptides enterocin 1071 A and 1071 B, as biological preservatives, versus that of conventional artificial preservatives was evaluated in the fish spread prototype. Three batches of fish spread were prepared: one containing the enterocin crude extract; the second a combination of sodium benzoate and potassium sorbate, while the third batch containing no preservatives served as the control. Microbiological- and histamine tests coupled with organoleptic monitoring and pH testing were carried out over a 21-day period. It was concluded that although enterocins 1071A and 1071B had some preserving effect in the fish spread, the artificial preservative combination was the superior preserving agent. However, neither the biological preservatives nor the artificial preservative combination succeeded in providing a satisfactory shelf life. The preserving agents used in this study were however not necessarily included at optimum levels and higher levels could possibly lead to an improved shelf life. The influence of two processing temperatures [121°C (249.8°F) and 116°C (240.8°F)] and two food container types (retortable pouch and can) on the sensory quality characteristics of the Chakalaka hake-prototype was investigated. The results indicated that the shorter processing time obtained with a higher processing temperature resulted in a product of better sensory quality. The sensory quality characteristics of Chakalaka hake processed in cans at 121°C were closest to that considered desirable for the product. AFRIKAANSE OPSOMMING: Die fokus van hierdie studie was die ontwikkeling van voedselprodukte geproduseer uit die nekvleis van stokvis (Merluccius capensis) met die doeI om waarde by stokviskoppe te voeg. Die volgende produk-prototipes is ontwikkel: 'n dik vissop met 'n kerriegeur (verpak in regopstaande sakkies), 'n vissmeer (verpak in plastiekomhulsels) en Chakalaka hake (verpak beide in blikkies en retortbestande sakkies). 'n Formule vir visaftreksel, wat as 'n basis-bestanddeel in die drie produk-prototipes gebruik is, is ook gestandaardiseer. Rakleeftydstudies het 'n belangrike deel van die ontwikkelingsprosesse van die verkoelde produk-prototipes, d.i. die dik vissop en die vissmeer, uitgemaak, Rakleeftydbepalings het mikrobiologiese toetsing, gebaseer op vasgestelde mikrobiologiese standaarde, sowel as die monitor van sensoriese eienskappe en pH metings behels. Proksimale chemiese- en mineraal analises is uitgevoer op gevriesdroogde monsters van die ontwikkelde produk-prototipes. Die effektiwiteit van die antimikrobiese peptiede enterosien 1071 A en 1071 B, as biologiese preserveermiddels, is ondersoek in vergelyking met dit van konvensionele kunsmatige preserveermiddels in die vissmeer-prototipe. Drie mengsels vissmeer is berei waarvan die eerste enterosien kru-ekstrak bevat het; die tweede 'n kombinasie van natrium bensoaat en kalium sorbaat, terwyl 'n derde mengsel geen preserveermiddels bevat het nie en gedien het as kontrole. Mikrobiologiese- en histamien toetse is gelyklopend met organoleptiese monitering en pH metings oor 'n tydperk van 21 dae op monsters van die drie vissmeermengsels uitgevoer. Die ondersoek het getoon dat enterosien 1071 A en 1071 B wel 'n mate van bederfwering in die vissmeer meegebring het, maar dat die kunsmatige preserveermiddelkombinasie 'n beter preserveringseffek gehad het in die produk. Nie die biologiese preserveermiddels óf die kunsmatige preserveermiddelkombinasie kon 'n bevredigende rakleeftyd teweegbring nie. Die preserveermiddels in hierdie studie is egter nie noodwendig in optimale hoeveelhede gebruik nie en hoër vlakke kan moontlik tot 'n verbeterde rakleeftyd lei. Die effek van twee prosesseringstemperature [121 °C (249.8°F) en 116°C (240.8°F)], sowel as twee verpakkingstipes (retortbestande sakkie en blik), op die sensoriese kwaliteitseienskappe van die 'Chakalaka hake' -prototipe is ondersoek. Die resultate het aangedui dat die korter prosesseringstyd verkry met 'n hoër prosesseringstemperatuur, gelei het tot 'n produk van beter sensoriese gehalte. Die sensoriese kwaliteitseienskappe van 'Chakalaka hake' geprosesseer in blikke by 121°C was die naaste aan dit wat beskou word as gewens vir die produk.

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26

Agostini, Vera Natalie. "Climate, ecology, and productivity of Pacific sardine (Sardinops sagax) and hake (Merluccius productus) /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/5377.

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Oluwole, Adebanji Olasupo. "Modified atmosphere packaging and quality of fresh Cape hake (Merluccius capensis) fish fillets." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/95967.

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Thesis (MScFoodSc)--Stellenbosch University, 2014. ENGLISH ABSTRACT: Fresh ready-to-cook fish fillets are prone to rapid loss of freshness and other quality attributes, as well as accelerated growth of spoilage micro-organisms under sub-optimal storage conditions. Cape hake (Merluccius capensis) is an important seafood in South Africa; however, rapid loss of quality and eventual spoilage is a problem limiting the economic potential. Thus, the aim of this study was to investigate the effects of active (40% CO2 + 30% O2 + 30% N2) and passive (0.039% CO2 + 20.95% O2 + 78% N2) modified atmosphere packaging (MAP) under different storage temperatures (0°C, 4°C, and 8°C) on the quality attributes of Cape hake (Merluccius capensis) fish fillets. This was achieved by investigating the effects of MAP (with or without absorbent pads) and storage temperature on quality attributes (microbial, physicochemical and sensory), changes in composition and concentration of volatile compounds (VOCs) and shelf life of Cape hake fillets. Modified atmosphere packaging, storage temperature and the use of absorbent pads had a significant (p < 0.05) impacts on physicochemical properties of Cape hake fillets during refrigerated storage. Highest storage temperature (8°C) led to accelerated deterioration of packaged Cape hake fillets. Generally, active MAP better maintained the quality attributes of Cape hake than passive MAP at 0°C and 4°C. Headspace gas composition of O2 and CO2 were significantly influenced by the storage time, temperature, MAP conditions and their interactions (p < 0.05). Irrespective of storage temperature, active-MA packaged fillets had lower pH values in comparison to fillets stored under passive-MAP. Drip loss was higher in active-MA fillets packaged without absorbent pad. Passive-MAP fillets did not show any drip loss. Absorbent pad was used to add value to MAP storage as MAP resulted in drip. The use of absorbent pad combined with low storage temperature maintained the firmness of hake fillets, across all temperatures. The interaction of MAP, absorbent pad and storage temperature had a significant effect on the aerobic mesophillic bacteria counts. Based on the aerobic mesophillic bacteria count fillets stored under active-MAP at 0°C (5.2 log cfu/g) was limited to day 12, while the fillet stored under passive-MAP at 0°C (log cfu/g) was limited to greater than day 3. Overall sensory acceptability of fillets decreased with increase in storage temperature across all treatments. Additionally, MAP had a significant (p < 0.05) impact on sensory attributes such as appearance and odour acceptability, with active-MA packaged fillets stored at 0°C having highest overall acceptability. A total of 16 volatiles were identified in Cape hake fillets, including 4 primary VOCs and 12 secondary VOCs. The VOCs associated with spoilage include tri-methylamine (TMA) (ammonia like), esters (sickeningly sweet) and sulphur group (putrid). MAP had a significant (p< 0.05) influence on volatile composition and concentration. Active-MA packaged fillets performed better during storage and had lower TMA value of 0.85% on day 12 in comparison with 7.22% under passive-MAP on day 6 at 0°C. The results obtained demonstrated that changes in volatile compounds were significantly (p< 0.05) influenced by storage duration, temperature and MAP. The development of high levels of VOCs and off-odour corresponded with high aerobic mesophillic bacteria count (≥ 5.5 log cfu/g). Based on these developments the storage life of Cape hake fillets packaged under active-MAP with absorbent pad and stored at 0°C was limited to 12 d, while the passive-MAP (control) fillets stored at 0°C was limited to 3 d. The use of active-MAP, in combination with absorbent pads and 0°C storage in addition to good hygienic practices, was effective in maintaining the postharvest quality of Cape hake fish fillets and led to higher shelf life. AFRIKAANSE OPSOMMING: Vars, gereed-vir-kook vis filette is geneig om gou hulle varsheid en ander gehalte kenmerke te verloor en die vervoegde groei van mikro-organismes wat bederf tydens stoor veroorsaak, vind plaas. Kaapse stokvis (Merluccius capensis) is in Suid-Afrika ‘n gewilde seekos maar die ekonomiese potensiaal daarvan word deur die feit dat dit so gou in gehalte afneem en bederf, beperk. Dus word daar met hierdie studie gepoog om die effek van aktiewe (40% CO2 + 30% O2 + 30% N2) en passiewe (0.039% CO2 + 20.95% O2 + 78% N2) aangepasde verpakking (MAP) onder verskillende stoortemperature (0°C, 4°C, en 8°C) op die gehalte kenmerke van Kaapse stokvis (Merluccius capensis) filette te ondersoek. Dit is gedoen deur om die effek van MAP (met of sonder kussinkies) en stoortemperatuur op die gehalte kenmerke (mikrobies, fisiochemies en sensories) asook veranderinge in komposisie en konsentrasie van vlugtige samestellings (VOCs) en die raklewe van Kaapse stokvis filette te ondersoek. Aangepasde atmosfeer verpakking, stoortemperatuur en die gebruik van absorberende kussinkies het ‘n groot impak (p < 0.05) op die fisiochemiese kenmerke van Kaapse stokvis tydens stoor in yskaste gehad. Hoë stoortemperature (8°C) het aanleiding gegee tot die vinnige bederf van verpakte Kaapse stokvis filette. Oor die algemeen het aktiewe MAP die gehalte van die Kaapse stokvis filette teen 0°C and 4°C beter bewaar. Die komposisie van O2 en CO2 is heelwat deur stoortyd, temperatuur, MA toestande en die interaksies tussen bogenoemde, beïnvloed (p< 0.05). By alle temperature het aktiewe MA verpakte filette laer pH waardes getoon in vergeleke met filette wat in onder passiewe MA verpak is. Die drupverlies was hoër in aktiewe MA filette verpak sonder absorberende kussinkies. Passiewe MAP filette het nie enige drupverlies getoon nie. Absorberende kussinkies is gebruik om waarde by te voeg tot MAP stoor aaangesien MAP gelei het tot drup. By alle temperature het die gebruik van absorberende kussinkies tesame met lae stoortemperature bygedra tot die behoud van fermheid. Die interaksie van MAP, absorberende kussinkies, en stoortemperatuur het ‘n groot effek gehad op die aerobiese mesofiliese bakterië telling. Weens die aerobiese mesofiliese bakterië telling is stoor van filette onder aktiewe MAP teen 0°C (5.2 log cfu/g) beperk tot dag 12, terwyl filette gestoor onder passiewe MAP teen 0°C ( log cfu/g) beperk is tot dag 3. Oor die algemeen het die sensoriese aanneemlikheid van filette sonder inasgneming van die behandeling, verklein met ‘n toename in stoortemperature. MAP het ook ‘n groot impak op die sensoriese kenmerke soos voorkoms, reuk, en aktiewe MA verpakte fillets gestoor teen 0°C is oor die algemeen die aanneemlikste. ‘n Totaal van 16 vlugtige substanse is in Kaapse stokvis identifiseer. Dit het vier primêre VOCs en 12 sekondêre VOCs ingesluit. Die VOCs wat met bederf assosieer word, sluit tri-metilamien (TMA) (soos ammoniak), esters (soet) en die swael groep (smetterig) in. MAP het ‘n groot (p < 0.05) invloed op die vlugtige komposisie en konsentrasie. Aktiewe MA verpakte filette het beter tydens stoor presteer en het ‘n laer TMA waarde van 0.85% op dag 12 gehad, in vergelyking met 7.22 % onder passiewe MAP op dag 6 teen 0°C. Die resultate toon dat veranderinge in vlugtige samestellings grootliks beïnvloed word (p < 0.05) deur stoortyd, temperature en MAP. Die ontwikkeling van hoë vlakke van VOCs, slegte reuke en verlies aan varsheid gaan tesame met hoë aerobiese mesofiliese bakterië telling (≥ 5.5 log cfu/g). Gegrond op hierdie tellings is die stoorleeftyd van Kaapse stokvis filette beperk tot dag 12, terwyl passiewe MAP (die kontrole) filette gestoor teen 0°C, beperk is tot dag 3. Om op te som, die gebruik van aktiewe MAP tesame met absorberende kussinkies en 0°C stoor asook goeie higiëniese praktyk, kon die na-oes gehalte van Kaapse stokvis filette behou en het gelei tot ‘n langer rakleeftyd.

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Vennemann, Ingo Heinrich. "Bacteria standards of merluccius capensis / paradoxus (Cape Hake) and other deepsea whitefish products." Thesis, University of Pretoria, 1996. http://hdl.handle.net/20.500.11838/2007.

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Thesis (PhD (Microbiology))--University of Pretoria, 1996. This study analysed the bacteria numbers of Hake products manufactured at 6 different levels of processing complexity, analyses were conducted at 20°C on Salt Water Agar (SWA) for a 48h incubation period. This enumeration method was suitable for indicating time and temperature related abuse in the processing system. This method was sensitive in indicating the level of processing complexity. The aerobic bacteria enumerations at 20°C (SWA) were compared to the current EU/FDA (European Union/Federal Drug Administration USA) standard procedure testing samples on Plate Count Agar, (PCA) incubated at 30 - 35°C. The method using SWA incubated at 20°C provided better and more accurate bacterial counts under "good" and "poor" manufacturing practice. The hurdle concept was applied, using gamma irradiation, temperature (Time), chemical preservatives and Vacuum packaging in an attempt to prolong the shelf life of fresh, uncooked Cape hake and Kingklip products. Radurization was effective only when the treated product was kept at refrigerated temperatures. Temperature was the most important control measure in extending the shelf life of the products. No shelf life extension was achieved with the use of chemical preservatives. Vacuum packaging was not effective in prolonging shelf life of the products and did not show any benefit when compared to oxygen permeable vacuum (microaerophilic) packaging. Determination of the total aerobic viable bacteria numbers at 20°C SWA, were suitable for estimating the shelflife of deepsea whitefish products.

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De, Almeida Louise. "The effect of sewage effluent from De Beers marine diamond mining operations on the expression of cytochrome P450 (CYP1A) and vitellogenin (vtg)." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1009440.

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Sewage effluents disposed into the marine environment from De Beers Marine Namibia diamond mining vessels have the potential to cause endocrine disruptive effects in marine organisms. Endocrine disruption refers to the alteration of the normal functioning of the endocrine system and various chemicals have the ability to mimic hormones, effecting endogenous hormone synthesis, transport, receptor interaction and intracellular signaling. The potential endocrine disruptive effects, caused by the release of different types of sewage effluents into the ocean, on fish species is a concern due to the commercial importance of fish species found in the mining area e.g. hake, sole, horse mackerel. Increased awareness of marine environmental degradation due to the presence of chemical contaminants has resulted in research being done on early warning systems, in the form of biomarkers. Cytochrome P450 monooxygenase 1A (CYP1A) and vitellogenin (vtg) are important proteins found in fish liver and blood, that have been used as biomarkers for the detection of pollutants in fish. CYP1A is a subfamily of the P450 superfamily of enzymes and catalyzes the oxidation, hydrolysis and reduction of exogenous and endogenous compounds (phase I reactions) and thus has the capacity to regulate the metabolism of several organic contaminants. CYP1A expression is altered by exposure to planar xenobiotic compounds e.g. polyaromatic hydrocarbons. Vtg is an important precursor for egg yolk proteins and plays a role in the growth and development of an oocyte. Expression of this protein is altered upon exposure to estrogenic compounds. The aim of this project was to isolate CYP1A from fish liver by differential centrifugation and optimize conditions for the CYP1A-mediated ethoxyresorufin-Odeethylase (EROD) assay and western blot analysis (to assess CYP1A expression). Another aim of this study was to evaluate the potential effects of biologically disruptive chemicals from sewage effluents, discharged into the marine environment, on the expression of CYP1A in two species of hake, Merluccius capensis and M. paradoxus (Cape hake). CYP1A in Cape hake is approximately a 60 kDa protein and the highest EROD activity was detected in the microsomal fraction after differential centrifugation. Optimal EROD assay conditions were observed at pH 7.5, a temperature of 25 °C, 10 μl of sample and a reaction time of 30 seconds. Enzyme stability assays indicated a drastic decrease in enzyme activity after 30 seconds. The EROD assay was not NADPH dependent but was limited by NADPH supply, with an increase of 300% in EROD activity being observed with the addition of 0.1 M exogenous NADPH. The addition of dicumarol (40 μM), a phase II enzyme inhibitor, showed a 232% increase in EROD activity. This is because dicumarol inhibited enzymes with the capacity to metabolize the product (resorufin) of the EROD reaction. With regard to western blot analysis, the optimal primary (rabbit antifish CYP1A peptide) and secondary (anti-mouse/rabbit antibody-horseradish peroxidase conjugate (POD)) antibody dilutions were determined to be 1:1000 and 1:5000, respectively. The comparison of CYP1A expression in Cape hake samples from De Beers Marine mining area and reference sites showed higher EROD activity (16.29 ± 0.91 pmol/min) in fish samples from the mining area in comparison to the reference site (10.42 ± 2.65 pmol/min). Western blot analysis was in agreement with the EROD assay results and a higher CYP1A expression was observed in fish from the mining sites. The increased CYP1A expression observed in fish from the mining area is not definitively an indication of a pollutant effect in the environment, as several environmental and biological factors (e.g. photoperiod and age) must also be considered before reaching this conclusion. Another aim of this study was to purify vtg from Cape hake blood samples. Cape hake vtg was purified from fish plasma by selective precipitation with MgCl2 and EDTA. Precipitated sample was subjected to anion exchange chromatography using fast protein liquid chromatography (FPLC). Vtg eluted as two broad peaks and had a molecular weight above 200 kDa. SDS-PAGE analysis also resolved smaller molecular weight proteins below 70 kDa, which were thought to be vitellogenin cleavage proteins, lipovitellin and phosphovitins. Western blot analysis was performed; however, it did not produce any conclusive results. The purification of vtg enables further studies in characterizing this protein and developing assay aimed at detecting estrogenic pollutants in the marine environment

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Ho, Thomas. "Feed attractants for juvenile chinook salmon (Oncorhynchus tshawytscha) prepared from hydrolysates of Pacific hake (Merluccius productus)." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/12651.

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The incorporation of soybean meal in aquaculture diets can lower feed ingredient costs, but also produces organoleptically unfavorable conditions for several salmon species. Addition of feed attractants could mask the undesirable tastes associated with soybean meal, enhance palatability of the diet, and increase feed intake. The objective of this study was to assess the feasibility of utilizing hydrolysates from Pacific hake as feed attractants in the diet of juvenile Chinook salmon. A 5-week palatability feeding trial was conducted to assess hydrolysates produced by Alcalase or Flavorzyme proteolysis of Pacific hake, compared to commercial feed attractants (krill meal and screen 1 & 2), as feed attractants in diets containing 20% soybean meal. These were compared with diets having no added feed attractants (negative control) and no soybean meal (positive control). All of the fish fed the soy-based diets had significantly (p<0.05) lower growth parameters when compared with fish fed the fishmeal based positive control diet. However, addition of Alcalase hydrolysate, krill or screen 1 provided increases in fish weight gain, feed efficiency ratio, and specific growth rate (p<0.05) compared with fish fed the negative control soy-based diet. The percent of feed dispensed that was not consumed by the fish was lowered (p<0.05) with the use of these three aforementioned attractants when compared to fish fed the negative control diet. Increased daily and total feed intake were also observed for the fish fed the Screen 1 coated diets (p<0.05). Fish fed Alcalase or Flavorzyme hydrolysate containing diets were tested for the presence of Kudoa spores, which were not detected in any of the fish tested. This study demonstrated the potential for Pacific hake, an underused marine source, to be converted to a feed attractant to help minimize the problems associated with dietary use of soybean meal in salmon aquaculture.

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Iyambo, Abraham Apere. "The structure and physicochemical properties of frozen Atlantic cod (Gadus morhua) and Namibian hake (Merluccius capensis)." Thesis, University of Surrey, 1994. http://epubs.surrey.ac.uk/844339/.

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Fish muscle proteins undergo complex physicochemical changes during frozen storage which result in the toughening of muscle and unpalatability. The aim of this thesis was to examine the aggregation of fish proteins as a result of frozen storage, in particular the effect of formaldehyde on proteins. Atlantic cod (Gadus morhua) and Namibian hake (Merluccius capensis and Merluccius paradoxus) muscle proteins were characterised and differentiated by electrophoretic and immunological approaches. The nature of the chemical bonds involved was elucidated by the use of reagents capable of breaking the non-covalent and covalent bonds. Conformational changes of the protein were investigated by both immunological and chemical techniques. Structural and textural changes on frozen storage in the presence of formaldehyde were examined by microscopic, deformation-compression analysis and dynamic mechanical testing. In addition, a lysosomal enzyme (Trimethylamine oxidase) which is responsible for the toughening of gadoid fish muscle during storage was characterised. Electrophoretic separation of the sarcoplasmic proteins from Merluccius capensis and Merluccius paradoxus confirmed the biological closeness of the two species. A 19kD protein band from M. capensis, excised from the SDS gel, was used for the production of polyclonal antibodies as analysed by an Enzyme Linked Immunosorbent Assay (ELISA). Formaldehyde and frozen storage augmented the extent of protein insolubilisation. The results of this study showed conclusively that formaldehyde is only one of many factors involved in the denaturation of fish proteins during frozen storage. List of objectives of the project. The objectives were: to characterise the fish muscle proteins and differentiate between the Namibian hake species Merluccius capensis and Merluccius paradoxus; to elucidate the chemical aspects related to solubility and foaming of fish muscle proteins in the presence of formaldehyde; to assess structural and textural changes in frozen and formaldehyde treated fish proteins by microscopy and viscoelastic measurements; to examine the changes in sulphydryl, disulphide and hydrophobic groups during frozen storage; to examine the changes in sulphydryl, disulphide and hydrophobic groups in the presence of formaldehyde; to monitor the degradation of trimethylamine oxide, formaldehyde and trimethylamine during frozen, storage of fish; and to characterise the enzyme TMAOase and to assess the effect of inhibitors.

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Ross-Gillespie, Andrea. "Modelling cannibalism and inter-species predation for the Cape hake species Merluccius capensis and M. paradoxus." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20519.

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The hake fishery is South Africa's most valuable and harvests two morphologically similar species, the shallow- water Cape hake Merluccius capensis and the deep-water Cape hake M. paradoxus. Since 1948, annual catches have exceeded 50 000 tons and the current total allowable catch (TAC) is about 150 000 tons, a quantity informed by assessments of the hake resource. Current assessments on which management is based use single-stock models that ignore food-web effects. Usually including such interactions in assessments is problematic because of the complexity of food webs. In the case of Cape hake, however, cannibalism and inter-species predation form a very large component of hake mortality and food consumption, thus making a multi-species model not only more feasible but also likely more reliable. A comprehensive multi-species model incorporating these interactions was last investigated in 1995. Since then, substantially more data have become available, and hake single-species assessments have developed considerably, inter alia now including the ability to take careful account of species differentiation. Additionally, with increased computer processing power, more sophisticated modelling can now be attempted than was possible 20 years ago, rendering an update and refinement of the 1995 analyses timeous. The thesis uses mathematical methods to model hake-on-hake predation and cannibalism in hake populations explicitly by incorporating an additional mortality term to account for these interactions. Information from stomach samples obtained on hake research surveys on predator and prey lengths, as well as on the proportion of hake in the diet of hake predators, is then included when fitting the model to data. Chapter 1 contains a brief introduction to the work. Chapter 2 provides background information on the Cape hake fishery and its management, as well as pertinent information on the biology and diet of the hake (and related fish) from the literature that is relevant to the development of the model constructed in this thesis. Chapter 3 lays out the data available for assessing the Cape hake populations: abundance indices together with catch and catch-at-size data for the standard non-predation model, and hake stomach content data for the years 1999-2013 to inform the predation component of multi-species model developed. Chapter 4 provides the details for the standard hake assessment model used at present to inform management of the stocks. This model forms the basis for the multi-species model developed incorporating predation, which is presented in Chapter 5. The remaining Chapters of the thesis present the results and discussions (Chapter 6), possible future development of this model (Chapter 7) and a brief summary of the main findings of the thesis (Chapter 8).

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33

Santos, André Martins Vaz dos. "\"Identificação de estoques da merluza, Merluccius hubbsi Marini, 1933 (Gadiformes: Merlucciidae) na Região Sudeste-Sul do Brasil\"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/21/21131/tde-09042007-161610/.

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A merluza, Merluccius hubbsi Marini, 1933, é uma espécie demerso-pelágica típica da região Sudeste-Sul do Brasil, presente entre 21°S e 34°S. Capturada em pequenas quantidades pelas frotas de arrasto, a partir de 2001 tornou-se alvo de pescarias na plataforma externa e talude superior e, desde então, tem apresentado claros sinais de sobrepesca. Estudos sobre o crescimento, a mortalidade e a reprodução apontavam a necessidade de identificar os estoques de merluza na região Sudeste-Sul, visando o adequado ordenamento de sua pescaria, sendo este o objetivo do presente estudo. Com esta finalidade, exemplares da coleção do Museu de Zoologia da USP, otólitos de exemplares juvenis da coleção do Laboratório de Ictiofauna do Instituto Oceanográfico e exemplares coletados em 2004, junto às frotas pesqueiras no Rio de Janeiro, em Santos, em Itajaí e em Rio Grande, no verão e no inverno, foram utilizados para procurando identificar variações geográficas. Foram analisados dados sobre caracteres morfométricos e merísticos, sobre o crescimento de juvenis e de adultos e sobre a reprodução. Os caracteres morfométricos não variaram; os caracteres merísticos apresentaram maiores valores ao sul de 33°S; o crescimento de juvenis e adultos é diferencial entre as regiões, associado à diferentes épocas de desova, com pico no verão na região Sudeste e, no inverno na região Sul. Foram identificados dois estoques: um no sudeste, entre 21°S e 29°S, e outro no sul, entre 29°S e 34°S, este último compartilhado com o Uruguai e a Argentina. Para a gestão imediata da pescaria de M. hubbsi, sugere-se para os dois estoques, restringir a pesca de arrasto durante quatro meses, sendo nos dois primeiros entre 250 e 500 m e nos dois últimos entre 100 e 250 m. Para o estoque sudeste esta restrição deve ser aplicada, para a área entre 21°S e 25°S, de outubro a janeiro e, para a área entre 25°S e 29°S, de novembro a fevereiro. Para o estoque sul a restrição deve abranger a área entre 29°S e 34°S, e vigorar entre abril e julho. The Argentine hake, Merluccius hubbsi Marini, 1933, is a demersal-pelagic fish inhabiting the South and the Southeast Brazilian area, between 21°S and 34°S. Since 2001, this species has been strongly targeted by trawlers operating at the external continental shelf and the slope. Previous studies about growth, mortality and reproduction pointed the necessity to identify stocks of this species which is the objective of this paper. Samples from the Museu de Zoologia USP collection, otoliths from juveniles fishes from the Ictiofauna Laboratory - IOUSP collection, and specimens collected during Summer and Winter of 2004 from fishing boats operanting in Rio de Janeiro, Santos, Itajaí and Rio Grande were used to analyze geographic variations. Morphometric and meristic data, juveniles and adults growth and reproduction characteristics were analysed. The morphometric characters did not present any variation, instead meristic counts tended to be larger in direction to south of 33°S. Juveniles and adults growth are different between the south and the southeast regions, and associated to different spawning periods, which is in the Summer and in the Winter, respectively. Two stocks were identified: one in the Southeast, between 21°S and 29°S, the other one in the south between 29°S and 34°S, the last one shared with Uruguay and Argentina. In order to manage these stocks, it is suggested the prohibition of the fishery activity during four months, the first two at depth between 250 and 500 m and the last two between 100 and 250 m. For the Southeast stock this restriction would be applied between 21°S and 25°S from October to January and between 25°S and 29°S from November to February. For the south stock the prohibition would be adopted in the area between 29°S and 34°S from April to July.

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Dorn, Martin William. "Hierarchical models of fishing behavior by factory trawlers in midwater-trawl fishery for Pacific hake (Merluccius productus) /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/5288.

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Angelini, Silvia <1986&gt. "Towards an Ecosystem Approach to Fisheries for Nephrops Norvegicus and Meluccius Merluccius Inhabiting the Central Adriatic Sea." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7380/1/Angelini_Silvia_tesi.pdf.

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This study presents the development of a Model of Intermediate Complexity for Ecosystem assessments (MICE) for testing management scenarios for the stock of European hake (Merluccius merluccius) and Norway lobster (Nephrops norvegicus) inhabiting the Central Adriatic Sea. These two species represent the target species, as well as the predators, of this study. They are mainly fished by Italian and Croatian bottom trawl fishery, accounting for both the highest landings and commercial value among demersal species in the area. The specific circulation of the Adriatic Sea is responsible for strong nutrient recycling processes within this area, resulting in a rich fishing ground extensively exploited by Italian and Croatian fishing vessels, make it an interesting case study for the development of an Ecosystem Approach to Fisheries (EAF). Here, an EAF was developed using the MICE approach, since it is well adapted to test specific management questions, as required by this study. The MICE was developed in a step-wise manner. Firstly, single-species stock assessments for both the target species were pursued, allowing the evaluation of the state of these resources and permitting the production of the input values to be included within the MICE. Secondly, the diet of the target species were examined and prey items portioned in four groups; consumption of each prey group by each predator was modelled using a Holling Type II functional response. Finally, predator and prey dynamics were linked within the MICE model, using a modified biomass dynamic model to project them into the future and testing different management strategies. The best management scenario resulted to be the protection of adults, which produced the most beneficial results for both predators and prey groups.

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36

Angelini, Silvia <1986&gt. "Towards an Ecosystem Approach to Fisheries for Nephrops Norvegicus and Meluccius Merluccius Inhabiting the Central Adriatic Sea." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7380/.

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This study presents the development of a Model of Intermediate Complexity for Ecosystem assessments (MICE) for testing management scenarios for the stock of European hake (Merluccius merluccius) and Norway lobster (Nephrops norvegicus) inhabiting the Central Adriatic Sea. These two species represent the target species, as well as the predators, of this study. They are mainly fished by Italian and Croatian bottom trawl fishery, accounting for both the highest landings and commercial value among demersal species in the area. The specific circulation of the Adriatic Sea is responsible for strong nutrient recycling processes within this area, resulting in a rich fishing ground extensively exploited by Italian and Croatian fishing vessels, make it an interesting case study for the development of an Ecosystem Approach to Fisheries (EAF). Here, an EAF was developed using the MICE approach, since it is well adapted to test specific management questions, as required by this study. The MICE was developed in a step-wise manner. Firstly, single-species stock assessments for both the target species were pursued, allowing the evaluation of the state of these resources and permitting the production of the input values to be included within the MICE. Secondly, the diet of the target species were examined and prey items portioned in four groups; consumption of each prey group by each predator was modelled using a Holling Type II functional response. Finally, predator and prey dynamics were linked within the MICE model, using a modified biomass dynamic model to project them into the future and testing different management strategies. The best management scenario resulted to be the protection of adults, which produced the most beneficial results for both predators and prey groups.

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MacIntosh, Denny C. "The characterization of the proteolytic enzyme(s) responsible for the post mortem softening of silver hake (Merluccius bilinearis)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq39681.pdf.

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Jeffrey, Jennifer Alice. "Growth variation of silver hake (Merluccius bilinearis) larvae in relation to oceanographic conditions on Western Bank, Scotian Shelf." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0018/MQ57299.pdf.

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Jayiya, Terence Phinda. "Modelling the relative impacts of trawling and longlining on Cape hake Merluccius capensis on the inshore Agulhas bank." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/6105.

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Bibliograpy: leaves 87-101. A Geographic Information System (GIS) is used to elucidiate vertical and horizontal patterns of distribution of Merluccius capensis on the inshore south coast (20°-27°E) of South Africa. Catch data used to compare the size distribution in catches made by commercial trawls and longlines off the South Coast (20°E). Results show that M.capensis size increases with depth and that the distribution of fish < 30 cm is mostly west of 23° E with isolated pockets east of that region. No seasonal differences were found in the distribution of this species. Spatial mapping of survey trawl and longline grounds of the Agulhas bank whereas longlines operate over rocky areas. Size comparisons of the catches of the two fishing methods reveal that longlines catch very few fish that are < 60 cm whereas trawl cataches are dominated by M. capensis of length < 60 cm. Analyses also revealed sex compostion in longline cataches to be different to that of trawls. All these results are discussed in relation to the ecology of M. capensis and the areas where data come from. Using size selectivity properties, the potential impacts of longlining and commercial trawling on the South Coast M. capensis (east of 20° E) are modelled with a yield per recruit and spawner biomass per recruit model. First, the age-specific selectivity vectors of the two fleets are estimated from catch data (length frequencies).

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Silva, Valle Mayra Zelena. "Evaluación de marcadores nucleares por EPIC-PCR y amplificación cruzada para estudios poblacionales en Merluccius gayi peruanus en el mar peruano." Bachelor's thesis, Universidad Nacional Mayor de San Marcos, 2010. https://hdl.handle.net/20.500.12672/873.

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La merluza peruana Merluccius gayi peruanus es una especie demersal con una gran importancia económica, necesariamente se deben hacer investigaciones de este tipo con la finalidad de conocer mejor al recurso para poder así tener mejores parámetros y facilitar su mejor aprovechamiento. De la merluza peruana, se posee escasa información acerca del componente genético poblacional. Debido a la carencia de esta información, el objetivo del presente trabajo fue caracterizar genéticamente las poblacionales de Merluccius gayi peruanus (periodo mayo, 2002) usando marcadores nucleares intrónicos: AldoC1 (AldolasaC intron 1), CK7 (Creatin Kinasa intron 7), GH5 (Hormona de Crecimiento intron 5) y Microsatélites (Mmer-hk9b). Las estrategias que se emplearon fueron EPIC-PCR y amplificación cruzada. El análisis estadístico realizado en la presente investigación demostró que las poblaciones estudiadas, de merluza constituyen una sola unidad poblacional. Palabras Claves: Optimización, PCR, marcador microsatélite, marcador EPICs, Merluccius gayi peruanus. ---Peruvian hake Merluccius gayi peruanus is a demersal species of great economic importance, necessarily must make such research in order to better understand the resource and to have better parameters and facilitate the best use. For the Peruvian hake, it has little information about the population genetic component. Due to the lack of this information, the purpose of this study was to characterize genetically the population of Merluccius gayi peruanus (period May, 2002) using intronic nuclear markers: AldoC1 (AldolasaC intron 1), CK7 (Creatine kinase intron 7), GH5 ( Growth hormone intron 5) and microsatellites (MMER-hk9b). The strategies used were EPIC-PCR and cross-amplification. The statistical analysis in this investigation showed that the populations studied, as a single hake population structure. Tesis

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Oré, Chávez Daniel Saúl. "Estructura Genética de la población de merluza meruana (Merluccius Gayi Peruanus) (Primavera, 2001) usando variantes de secuencia de la región de control Mitocondrial." Bachelor's thesis, Universidad Nacional Mayor de San Marcos, 2011. https://hdl.handle.net/20.500.12672/1358.

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La merluza peruana (Merluccius gayi peruanus) sostiene una pesquería importante en el país. Actualmente la evaluación y manejo de este recurso asume la presencia de un solo stock en el mar norperuano, sin embargo, observaciones realizadas en 1997 sugieren la existencia de dos stocks, al norte y sur del paralelo 6°S. El objetivo del presente estudio es evaluar mediante el uso de marcadores mitocondriales la presencia de una o dos unidades poblacionales de merluza, para lo cual se amplificó la región de control mitocondrial parcial y completa, detectándose las variantes con dos técnicas Single Strand Conformational Polymorphism (SSCP) y secuenciamiento directo, respectivamente. Se observa una alta diversidad haplotípica y baja diversidad nucleotídica, con una escasa diferenciación y estructura genética, con la presencia de dos posibles líneas matrilineales yuxtapuestas geográficamente. Así mismo existe evidencia de que la población atravesó un reciente evento de expansión poblacional a finales del Pleistoceno. En conclusión, la merluza peruana comprende una sola unidad panmíctica en el mar norperuano sin presencia de una estructuración genética en sus poblaciones, lo cual apoya la hipótesis de un solo stock, siendo necesario el empleo de otros marcadores como los microsatélites para efectuar análisis multilocus a fin de tener mayores criterios que apoyen la hipótesis. -- Palabras clave: Merluccius, Merluza peruana, ADN mitocondrial, dinámica poblacional. Peruvian hake (Merluccius gayi peruanus) supports a major fishery in the country. Currently the evaluation and management of this resource assumes the presence of a single stock in the north peruvian sea, however, observations in 1997 suggests the existence of two stocks in the north and south of 6 ° S. The aim of this study is to evaluate using mitochondrial markers the presence of one or two units of hake population, which was amplified for the mitochondrial control region of partial and complete, detected with two techniques: Single Strand Conformational Polymorphism (SSCP) and sequencing, respectively. A high haplotype diversity and low nucleotide diversity, with differentiation and structure genetic low, with the possible presence of two matrilineal lines juxtaposed geographically. Likewise there is evidence that the population underwent a recent population expansion event in the late Pleistocene. In conclusion, the Peruvian hake comprises a single panmictic unit north peruvian sea without the presence of genetic structure in populations, which supports the hypothesis of a single stock, requiring the use of other markers such as microsatellites for analysis to multilocus to have better criteria to support the hypothesis. Key words: Peruvian hake, Merluccius, AND mitochondrial, dynamics of populations. Tesis

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42

Ferrer, Maza Dolors. "Effects of parasitism on the condition and reproductive capacity of three commercially exploited fish species in the Mediterranean Sea." Doctoral thesis, Universitat de Girona, 2016. http://hdl.handle.net/10803/385347.

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This PhD thesis evaluates the links between parasitism, condition and reproduction of mature female individuals of three of the most captured fish species in the western Mediterranean Sea: European hake, Merluccius merluccius; red mullet, Mullus barbatus, and European anchovy, Engraulis encrasicolus. Indicators of fish energy reserves (total lipid content in liver, muscle and gonads) and reproductive capacity (fecundity and egg quality) were evaluated, as were the prevalence and intensity of infection by metazoan parasites. By evaluating these relationships, this thesis also provides essential data on the health and reproduction of these three fish species, such as the spawning strategy. La present tesi doctoral avalua els vincles entre parasitisme, condició i reproducció en femelles adultes de tres de les espècies més capturades a la Mediterrània occidental: el lluç europeu, Merluccius merluccius; el roger de fang, Mullus barbatus, i el seitó, Engraulis encrasicolus. Amb aquesta finalitat, es varen avaluar els indicadors de les reserves energètiques (contingut total de lípids en el fetge, musculatura i gònades) i la capacitat reproductiva (fecunditat i qualitat de la posta), així com la prevalença i intensitat de la infestació per paràsits metazous.Paral·lelament a l’anàlisi d’aquestes relacions, aquesta tesi també proporciona dades essencials sobre la salut i reproducció d’aquestes tres espècies, com per exemple l’estratègia reproductiva.

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Barriga, Rivera Edward. "Variación en los patrones de distribución y abundancia de merluza (Merluccius gayi peruanus Ginsburg, 1954) frente a la costa norte de Perú (2004 - 2014)." Master's thesis, Universidad Nacional Mayor de San Marcos, 2017. https://hdl.handle.net/20.500.12672/7251.

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Publicación a texto completo no autorizada por el autor Analiza los cambios en los patrones de distribución y abundancia de merluza, a partir de la estandarización de la tasas de captura de una serie temporal de 2004 a 2014, utilizando un modelo lineal generalizado cuyas variables explicativas son año, mes, flota, sector, estrato y la variable ambiental ONI (Oscillation El Niño Index). Las variaciones espaciales y temporales de la tasa de captura estandarizada, como indicador de abundancia relativa, indican que el stock disponible de merluza experimentó cambios en su distribución y abundancia entre 2004 y 2014, mostrando tres escenarios: el primero entre 2004 y 2006 con tendencia descendente de los niveles de abundancia y distribución, integrado por merluzas con talla media que decayó de 31 a 26 cm, un segundo escenario entre 2007 y 2011 con niveles de abundancia casi constantes y notorias fluctuaciones estacionales en su abundancia, distribución y talla media, influenciados por la variabilidad estacional de la ESCC, y un tercer escenario entre marzo de 2012 y mitad de 2014 con niveles de abundancia superiores a los escenarios anteriores, los más altos del periodo analizado, integrado por ejemplares con talla media de 35 cm. En general, a partir de 2007 la población de merluza frente a la costa norte del Perú, mostró tendencias positivas en su distribución, abundancia y estructura poblacional, atribuibles a la presencia de condiciones favorables del medio marino y a las medidas de ordenamiento pesquero implementadas en este periodo. Tesis

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Boyd, Danielle Winona. "Establishing a baseline for evaluating changes in fish body condition and population dynamics of Cape hake (Merluccius capensis and M. paradoxus) in South Africa." Bachelor's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13256.

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Includes bibliographical references. Standard weight (Ws) equations were developed and relative weight (Wr) indices calculated for both shallow-water (Merluccius capensis) and deep-water (M . paradoxus) Cape hake. The aim was to provide fixed baselines and Wr indices to aid understanding of temporal and spatial variability in fish condition . Baselines were calculated using the empirical percentiles (EmP) method applied to length (L) – weight (W) data collected by research surveys on the South African west and south coasts, from 1983 to 2013 . Four quadratic Ws equations for each species were generated, based on the following weight statistics for each size class j : first quartile, median, third quartile and mean. Median Ws equations were chosen for the baseline for shallow-water hake (log₁₀ Ws=-2.491 + 3.33 8 *(log₁₀ L)-0.065 *(log₁₀ Lj)²) and deep-water hake (log₁₀ Ws =- 2.161 + 2.930*(log₁₀ L) + 0.0456 *(log 10Lj)²). Shallow-water hake was found to be the heavier of the two species at the same length. Wr indices display good condition values (>100%) for both species throughout all analyses . Fish condition for both species was best between 1988-2009, ranging from 50-1 65% for individual fish and 100 – 109% for annual averages. Monthly mean Wr indices peaked in June and October for shallow-water hake and July and October for deep-water hake. Mean Wr values were different for shallow-water hake on the south (105%) and west (103%) coasts. Deep-water hake showed no spatial variability in mean Wr values. There were no differences between mean Wr values of males and females between, and within, species. Future hake data may be compared to these Ws equation baselines and Wr indices to show changes in body condition for this commercially important stock.

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Hunt, Kim-Kelly. "The effects of an unidentified pathogen, ‘Frill on Gill’, on body condition of Cape hake Merluccius capensis, on the south coast of South Africa." Master's thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31391.

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The unidentified pathogen, known as 'Frill on Gill’ (FOG), infects the shallow-water Cape hake Merluccius capensis off the south and west coast of South Africa. This pathogen, a parasitic castrator, occurs on the gill filaments of infected fish. This study investigates the effects of this pathogen on the body condition of M. capensis on the south coast of South Africa, through the use of two body condition measures, condition factor and hepatosomatic index (HSI). A total of 24275 M. capensis were sampled, of which 825 (3.4%) were infected with the FOG pathogen. The smallest M. capensis infected with FOG was 10 cm, and the largest was 84 cm. The smallest uninfected M. capensissampled was 6 cm and the largest was 106 cm. The presence of FOG had a significant impact on the condition factor and HSI of M. capensis (three-way analysis of variance (ANOVA): p-value = 0.002, and p-value = 5.13e-09 respectively), with the effect of the pathogen varying with length. For fish with a total length smaller than 26 cm, infected M. capensis were in poorer condition than uninfected fish at the same length, with lower condition factors and HSI values. However, for M. capensis with lengths between 30 and 34 cm, 42 and 46 cm, 54 and 62 cm, and 78 and 82 cm, the condition factors of FOG infected fish were higher than uninfected fish. The HSI values of M. capensis infected with FOG also steadily increase above those of uninfected fish, for lengths greater than 42 cm. The lower body condition measures of uninfected M. capensis could be linked to the large amounts of energy that these fish expend during reproduction and gonad maturation. In contrast, M. capensis infected with FOG do not partake in the energy intensive task of reproduction. Merluccius capensis infected with FOG don’t contribute to reproduction, but still compete with uninfected M. capensis for resources. The effect of FOG as a type of parasitic castrator on the regulation of M. capensis populations could become a concern for fishery managers, as they reduce reproductive output and impact fish body condition.

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Cass-Calay, Shannon L. "The effects of prey availability and physical variables on the feeding and growth rates of larval Pacific hake, Merluccius productus, in the California Current region /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035896.

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47

Iitembu, Johannes Angala. "Trophic relationships of hake (Merluccius capensis Castelnau, 1851 and M. paradoxus Franca 1960) from the Northern Benguela current ecosystem (Namibia) : inferences from stable isotopes and fatty acids." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1020296.

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Two species of hake (Merluccius capensis and Merluccius paradoxus) account for most of Namibia’s fisheries catch, and they are important secondary consumers in the Benguela Current ecosystem. Inferences on their trophic relationships have been based mainly on stomach content analyses. However, such data are limited temporally because they represent only snapshots of recent feeding, and are quantitatively biased because of variation in the digestion rates of different prey. The principal aim of the thesis was to understand the trophic relationships of two hake species relative to each other, their known prey and top predators (demersal sharks) in the northern Benguela Current ecosystem (Namibia), using time-integrating trophic biomarkers. By using stable isotope (carbon and nitrogen) and fatty acid signatures of their muscle tissues, my overall objectives were to produce new knowledge about 1) hake ontogenic trophic relationships, 2) the contributions of different prey to hake diets, 3) hake dietary differences, and 4) some aspects of hake’s trophic relationships with demersal sharks. Tissues of hake (n=358), their potential prey (n=455), and demersal sharks (n=42) were collected between 2008 and 2012 during demersal bottom trawl surveys off Namibia, for stable isotope and fatty acid analyses. And more...

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Parkins, Colleen Ann. "Stable carbon and nitrogen isotope ratios in the shallow-water cape hake, merluccius capensis (castelnau) as indicators of trophic position and diet on the west and south coasts of South Africa." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/6156.

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Bibliography: leaves 44-53. 13C/12C and 15N/14N were used to indicate the trophic levels of the shallow-water Cape hake, Merluccius capensis (Castelnau) at three sites on the west coast of South Africa, and five sites on the south coast. Gut content analyses show only the very recent diet of hake, therefore stable carbon and nitrogen isotope ratios were used to show the longer-term diet, integrated over the turnover time of the muscle tissue and bone collagen analysed. 13C/12C is 1-2%₀ higher in the tissues of a consumer than its diet (DeNiro and Epstein 1978), the difference in 15N/14N between a consumer and its food being 3-4%₀ (DeNiro and Epstein 1981). Both 13C/12C and 15N/14N indicate trophic enrichment between hake muscle tissue and bone collagen, and the gut contents and prey, and show that small and large hake feed at different trophic levels, large hake tissues being slightly heavier in 13C than small hake tissues, and containing 2-4%₀ more 15N than muscle tissue and bone collagen, and the gut contents and prey, and show that small and large hake feed at different trophic levels, large hake tissues being slightly heavier in 13C than small hake tissues, and containing 2-4%₀ and more 15N than muscle tissue and bone collagen of small hake.

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Götz, Albrecht. "Assessment of the effect of Goukamma Marine Protected Area on community structure and fishery dynamics." Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005073.

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This study presents a detailed investigation into size, density and community structure of temperate marine reef fish in the medium-sized Goukamma Marine Protected Area (Goukamma MPA) and adjacent fishing grounds on the south coast of South Africa. The oceanographic conditions, the spatial distribution of the benthic community and the prevailing fishing effort are also described. Life history traits and per-recruit (PR) models for the principle target species, roman (Crysoblephus laticeps) are compared between the protected and exploited area. From the study results, various strategies are proposed for the use of MPAs in the conservation and management of linefish species along South Africa’s south coast. The distribution and topography of reefs in the protected and exploited sections of the study area were found to be comparable. Atmospheric pressure ranged from 992 to 1,032 mb, being significantly lower in summer. Wind speeds ranged from 0.7 to 71.3 km/h. Water temperatures ranged between 9.0 and 22.2 ºC and turbidity between 0.3 and 45.8 NTU. Water temperature and clarity were uniformly low in winter. In summer the water was generally warm, clear and stratified, with a thermocline at around 20 m, although intermittent upwelling events caused water temperature to decrease and clarity to deteriorate. Current speeds ranged between 0.11 and 2.59 km/h and were significantly higher in spring and autumn. Easterly currents prevailed in spring, summer and autumn and westerly and southerly currents in winter. Hake (Merluccius capensis), various resident reef fish and kob (Argyrosomus japonicus) were most frequently targeted by the local linefishery. A significant amount of illegal fishing was found to occur in the protected area. Fishing effort was found to be highest around the border of the MPA (2.7 boats/km²) and lowest in the core of the MPA (0.2 boats/km²). If law enforcement remains poor it may be necessary to adapt the management strategy to extend the reserve, thereby mitigating against illegal fishing and ensuring a core area of no exploitation. Various other alternatives were investigated and it was demonstrated that the amount of fish caught of legal size could be increased by about 23% and post-release mortality of undersized fish reduced by 50% through the introduction of a suit of restrictive measures. Randomly stratified underwater visual census (UVC) and controlled fishing were used to investigate the ichthyofauna and benthic community at protected and exploited sites in the study area. Resulting density and size data from 273 fishing sites and 177 point counts were analyzed using generalized linear models (GLMs). Fish communities were found to vary significantly, depending on the level of exploitation. Roman, the principle reef fish species targeted by the fishery had significantly higher densities within the protected parts of the study area (CPUE: 4.3 fish/anglerhour; UVC: 2.2 fish/point-count) as compared to the exploited part (CPUE: 3.4 fish/anglerhour; UVC: 1.8 fish/point-count), correlating strongly with the observed fishing effort. Also mean sizes were significantly higher in the protected area (299 mm from fishing survey and 233 mm from diving estimates) as compared to the exploited section (283 mm from fishing survey and 198 mm from diving estimates). Although other fish species also had significantly higher mean sizes at protected sites in most cases their densities were significantly lower. This suggests a top-down control of the fish community by the dominant predator (roman). The results of the UVC showed the diversity of the ichthyofauna to be significantly higher inside the protected area. Interestingly this did not apply to the results of the controlled fishing experiment where the diversity of fish in the catch was lower in the protected area - a result that may be explained by the selectivity of fishing for the most aggressive species – and a reminder of the limitations of controlled fishing experiments. Possibly the most important finding of the study revolved around the benthic community. These were significantly different at exploited and protected sites, with algae and crinoids more abundant at exploited sites. Crinoids are the principle food of roman and were low in abundance where roman abundances were high, suggesting that the dominant top predator reduced crinoids. Furthermore, it substantiates the correlation of roman abundance with fishing effort, since habitat preferences can be ruled out by the observed causal predator-prey distribution pattern. Low algae abundances at protected sites correlated with high strepie (Sarpa salpa) frequencies within the fish communities encountered there. Strepie, a shoaling and abundant benthic grazer, does not compete for food with roman, suggesting a high potential for coexistence of the two species. As expected, and found by other studies, life history traits of roman differed between protected and exploited sample-sites. With a significantly lower age-at-maturity and age-atsex- change, the exploited population showed a typical response to fishing effort. The sex ratio of this protogynous hermaphrodite was found to be sustained at healthy levels by phenotypic plasticity. However, one important additional factor was highlighted by the study; the average condition factor of the protected population was significantly lower (0.0283 g/cm³) compared to the exploited population (0.0295 g/cm³). This was probably due to the higher intra-specific competition for lower food abundance in the protected area. Interestingly the diving and fishing survey methods yielded similar mortality results for roman. Total mortality rate estimates derived from length frequency analysis from the diving and fishing survey were not different (0.32 and 0.29 y⁻¹, respectively) as were natural mortality rate estimates (0.24 and 0.19 y⁻¹, respectively). Natural mortality rate (M) estimates indicated by Pauly’s and Hoenig’s relationship were similar (0.25 and 0.23 y⁻¹, respectively). Detailed yield-per-recruit (Y/R) and spawner biomass-per-recruit (SB/R) analyses were presented for different levels of M, varying age-at-recruitment (tR) and fishing mortality (F). Current tR (7.60 y) and F (0.16 and 0.25 y⁻¹, from the diving and fishing dataset, respectively) suggests an optimal exploitation of the population in the exploited part of the study area. However, a separate SB/R analysis of the male part of the population showed their vulnerability to over-exploitation, even at reduced age-at-sex-change from fishing. There therefore remains a high risk of recruitment failure for the roman population. Of course MPAs can be used to measure stock status directly if the influence of factors such as cachability, habitat and sampling method on CPUE assessments can be limited or reduced. The experimental design in this study allowed for contemporary CPUE comparisons across the border of the Goukamma MPA. Results were similar to those obtained by the SB/R analyses. CPUE extrapolations therefore, using small MPAs, can provide reliable and consistent estimates, and offer a practical alternative to conventional assessment strategies. This study has highlighted the importance of ensuring a well structured and comprehensive survey design when undertaking a comparison of protected and exploited marine areas. The results provide a comprehensive framework for future management of the Goukamma MPA and other protected areas along the temperate coastline of South Africa.

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Dores, Sandra Isabel Martins das. "Avaliação da idade em pescada (Merluccius merluccius): métosos directos e indirectos." Master's thesis, 2012. http://hdl.handle.net/10400.1/10855.

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Dissertations / Theses on the topic 'Merluccius merlucciu'

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