Tesi sul tema "Merluccius capensis"

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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).

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.

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.

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

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...

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.

Dissertação mest., Gestão da Água e da Costa, Universidade do Algarve, 2007
Age and growth estimates of Cape hake (Merluccius capensis), in the waters off Namibia were described from 804 specimens collected during January and February 2003. Each specimen was aged twice using whole otoliths. Otolith growth measurements was taken and used in back-calculated length-at-age data of M. capensis. Direct average otolith growth measurements have shown that up to three false rings formed prior to the first annulus. Ogives demonstrated the differences in otolith diameter, location frequency between the annuli and false rings. A power fish length-otolith diameter relationship used for back-calculation is: (L = 1.39 * OD). The average back-calculated lengths for the first four years of life were 19.3, 25.6, 31.8 and 38.2 cm total fish length. Age composition, estimated from an age length key, indicated that juveniles and young fish predominate in survey and commercial catches. The von Bertalanffy growth parameters was (growth coefficient, K = 0.07; asymptotic length, = 123.13; = -1.5). Sexual maturity was reached at age 1.67 years. The high correlation between otolith weight and age permits the use of otolith weight as a substitute for future age assessments. 1717.1∞L0t Key