Dissertations / Theses on the topic 'Clarias gariepinus Fish culture'

Inadequate seed production has historically been a factor limiting the commercial culture of Clarias gariepinus. The need to determine the environmental requirements of larvae was identified, in order to facilitate their successful mass rearing in hatcheries. The effects of key environmental factors on the growth, survival and aspects of the behaviour of C. gariepinus larvae and juveniles were investigated under controlled conditions. A strong emphasis was placed on the interpretation of the observed responses in terms of the natural history of the animal. Larvae were obtained by artificially inducing and spawning feral adult broodfish. Larval growth rates were highest in the temperature range 26-33ºC, with a peak at 30ºC. Survival of larvae was high between 22 and 33ºC. The final temperature preferendum of juveniles, determined in a thermal gradient was 30ºC, and it was concluded that this temperature is probably optimal for most of the physiological processes of the animal. Larvae and juveniles displayed strong negative phototaxis. When reared under different photoperiod regimes, larval growth increased with longer dark periods, however a similar rate of mortality was recorded in all photoperiod treatments. The provision of cover was found to enhance larval growth under conditions of continual light (24L/OD), however under conditions of continual darkness (OL/24D) similar growth rates were recorded regardless of the presence or absence of cover. All growth rates in continual darkness (OL/24D) were higher than those in continual light (24L/OD), regardless of whether cover was provided or not. It was concluded that a OL/24D photoperiod is optimal for larval rearing. At salinities between 0 and 5% similar growth and mortality rates of larvae were recorded. At 7.5 % larval growth and survival rates were lower, and at 10 % all larvae died within 48 hours. The 96h-LCSO for unionised ammonia was found to be 2.3 mg/l. The cytological effects of unionised ammonia were evident as degenerative changes in the gill and liver tissues. In an investigation of tank hygiene, it was found that larval growth and survival rates were highest in tanks not cleaned at all. As the frequency of tank cleaning increased, the growth and survival rates of larvae decreased. When reared at densities ranging from 45-450/1, larval growth was found to be density dependent. A model of hatchery productivity (number larvae of standard size produced/time/vol.) was developed based on the density dependent nature of larval growth. The model predicts that maximum productivity, will be achieved at a rearing density of 1400/1. The high growth and survival rates obtained over a broad range of each environmental parameter investigated serve to explain how larvae survive and grow in their unstable floodplain habitat in nature. The broad environmental tolerances of C. gariepinus are of benefit with respect to the culture of larvae, as successful larval rearing is possible over a fairly wide range of environmental conditions.

A rationale is presented for a primary nursing strategy and an on-growing strategy for Clarias gariepinus (Burchell) culture in Africa, thus providing a potential model for the development of culture technology for the species. Existing information pertaining to the production strategies identified is reviewed, highlighting the attributes of African catfish for aquaculture. Some of the current deficiencies and inconsistencies in available information pertaining to controlled hatchery production are addressed. The early developmental stages of Clarias gariepinus are defined, in order to promote consistent use of terminology and help farmers better address the changing needs of their developing stock. The pattern of growth and survival of larvae and fry is investigated at higher stocking densities than those used experimentally to provide a database for planning full-scale commercial operations. Tank design and water flow rates appropriate for Clarias gariepinus in hatcheries are investigated and recommendations made. Finally, in order to promote maximal growth rates of hatchery stocks the maximum daily feed intake of larvae in relation to different feeding regimes is estimated based on rates of gastric evacuation and return of appetite. An overview of the controlled hatchery production of Clarias gariepinus is presented.

Thesis (MPhil (Animal Sciences. Aquaculture))--University of Stellenbosch, 2005.
In recent years there has been a renewed interest in the commercial culture of African Sharptooth Catfish. Its robust characteristics and its air breathing capabilities makes the African catfish a good candidate for culture in intensive recirculating systems. In light of the size variation in offspring spawned from undomesticated fish, that may eventually increase cannibalism, suitable methods for the quantification of some production performance parameters such as growth and health measurements need to be established for application in intensive catfish culture. In fish the condition factor (CF) reflects information on the physiological state of the fish in relation to its welfare. This factor is expressed as Fulton’s condition index, or the K-factor. African Sharptooth Catfish fry with average weight of 1.9g ± 0.7867 and average length of 59.375mm ±8.812 were equally allocated into ten 1000L-recirculating tanks. The fish were fed a commercial feed to apparent saturation at a frequency of 5 times per day. Sixteen fish were sampled out of each treatment. Weight (g) and length (mm) of each fish were recorded every seven days over a trial period of 175 days from which Fulton’s condition index K was calculated. Results were analysed for significant differences using one-way ANOVA and Tukey’s pair wise comparison test for the various parameters. Growth parameters (a = -5.083, b = 3.004, R2 = 99.4%) derived from the logarithmic relationship between body weight (W) and standard length (L) indicated an isometric growth through the duration of the trail. No significant differences (P>0.05) in condition factors between treatments were found at the beginning of the trail. Significant differences (P<0.05) were found at the end of the trail for weight between ponds and condition factor between treatments. No significant difference (P> 0.05) between length and treatments were found at the end of the trial. Mean condition factor was 0.856 ± 0.187. By using this information on condition factor for African catfish a K-factor calculation chart for African catfish could be calculated, to be used as a practical measurement tool to measure performance goals on catfish farms.

Thesis (Ph.D. (Agriculture)) --University of Limpopo, 2015
The ability to utilise dietary components differs between fish species. Digestive enzymes may be used to determine the efficiency of the digestive process. In this study, the activities of the digestive enzymes in Tilapia rendalli, Oreochromis mossambicus and Clarias gariepinus were explored. Protease, amylase, lipase and cellulase activities were measured in different parts of the digestive tract of the three fish species. The pH dynamics along the digestive tract were monitored. In all fish species, the presence of food led to a reduction in stomach pH. pH values of 1.54, 1.58 and 2.01 were recorded 12 hours after feeding in Oreochromis mossambicus, Tilapia rendalli and Clarias gariepinus respectively. Protease and amylase activities were significantly higher (P<0.05, ANOVA) in the tilapias than in Clarias gariepinus. The tilapias may be pre-adapted to produce more protease and amylase to digest plant material which is more difficult to digest compared to animal matter. In all species amylase activity was significantly higher in the proximal intestine than in the other parts of the digestive tract (P<0.05, ANOVA). The highest proteolytic activity was recorded in the distal intestines. This is because of the alkaline pH recorded in the proximal and distal intestines which favours for amylase and protease activity respectively. Lipase activities were not significantly different (P>0.05) in all species. Marginal cellulase activities were recorded in all species. It is inferred here that phylogeny and not diet may be the main factor influencing enzyme activities as all fish were fed a similar diet. Two locally available plant diets, kikuyu grass and moringa leaves, were tested as protein sources in the diet of a macrophagous fish, Tilapia rendalli (11.5±1 g). Nine diets (30% CP: 20 MJ/kg) were formulated by substituting fishmeal for kikuyu leaf meal (KLM) and moringa leaf meal (MLM). A control diet contained 10% fishmeal and no leaf meal. Fishmeal was replaced at 25, 50, 75 and 100% by KLM in diets: KLM 25, KLM 50, KLM 75 and KLM 100; then by MLM in diets MLM 25, MLM 50, MLM 75 and MLM 100. Each diet was fed to triplicate groups of fish for 60 days. The best growth (SGR, TGC) was in the control group. There was no significant (P>0.05) decrease in SGR and TGC when KLM replaced up to 50% fishmeal. There was a significant (P<0.05) decrease when MLM replaced >25% fishmeal. Kikuyu diets had no effect on villi height. A trend towards shorter villi was evident with increasing MLM. Digestive enzyme activities also decreased with increasing KLM and MLM vii levels in the diet. Hepatocyte degradation was higher in fish fed moringa-based diets. Anti-nutrients (polyphenols, tannins, saponins and phytate) in moringa may have contributed to the poor growth, irritation of the enterocytes and hepatotoxic effects. These results show that replacing up to 25% fishmeal with KLM is effective in reducing the costs without negatively affecting the growth performance or health of Tilapia rendalli. Adding MLM, even at the lowest level (25%) was expensive and resulted in compromised growth and health. The efficacy of KLM and MLM was also tested as alternative protein sources for Oreochromis mossambicus (12.5±1 g) a microphagous herbivore. The same diets used for Tilapia rendalli were fed to triplicate groups of twenty fish for 60 days. Linear regressions of feed intake, SGR, PER and protein ADC with increasing levels of leaf meal were significant (P<0.05). Superior growth performance, protein ADC and feed utilisation were also recorded in fish fed KLM-based diets than those fed MLM diets. When compared to Tilapia rendalli, Oreochromis mossambicus had superior growth performance and feed utilisation when fed the control diets and the lowest level of KLM. This was attributed to phylogeny. Protease, amylase and lipase decreased with increasing leaf meal levels and were higher in the intestine of fish fed KLMbased diets than those fed MLM-based diets. Fish fed MLM-based diets had higher number of goblet cells in the enterocytes, higher hepatocyte degradation and poor haematological parameters than those fed KLM diets. These adverse alterations were more pronounced in Oreochromis mossambicus compared to those observed in Tilapia rendalli feeding of the same diets. Cost benefit analysis also indicated that substitution fishmeal with KLM is a cheaper protein source in Oreochromis mossambicus diets. Kikuyu leaf meal may be used to replace up to 25% fishmeal without compromising the growth performance and health of Oreochromis mossambicus. Reduced growth and poor health was evident even at the lowest inclusion level of MLM. The effects of replacing fishmeal with KLM and MLM in the diets of a predatory omnivore, Clarias gariepinus were also investigated. The same KLM and MLMbased diets used in the previous experiments were used. Each diet was randomly assigned to triplicate groups of Clarias gariepinus (30.5±2 g) and fed to apparent satiation for 60 days. Significantly higher (P<0.05) growth performance, feed and viii protein utilisation was observed in Clarias gariepinus fed KLM diets compared to those fed MLM. Protein digestibility was higher in Clarias gariepinus fed the control diet than in both tilapias. However, in the treatment diets protein ADC was lower in Clarias gariepinus than in the tilapias. A decrease in the activity of digestive enzymes was also observed with increasing leaf meal level in the diet. This was attributed to the natural feeding habits and digestive adaptations of the different fish species. No histological alterations were found in liver of fish fed the control diet. Increased hepatocyte degradation was seen in fish fed higher levels of KLM and MLM in the diet. The enterocytes showed a significant increase in the number of goblet cells with increasing levels of MLM. Villi height decreased significantly (P<0.05) when MLM replaced >75 fishmeal. The damage to the hepatocytes and enterocytes as well as the poor health condition shown by haematological parameters was more pronounced in Clarias gariepinus than in the tilapias. This suggests that the predatory fish is not equipped to utilise high levels of leaf meals in its diet. The results of this study indicate that KLM can replace up to 25% fishmeal and that adding MLM resulted in reduced performance. Higher profit index and lower incidence cost was observed KLM diets than in MLM diets. Anti-nutrients in the leaf meals were the main factors leading to reduced feed intake and poor growth in fish fed the plant-based diet. Therefore, a subsequent study was undertaken to determine the efficacy of exogenous enzyme supplementation to reduce the negative effects of anti-nutrients and improve fish growth. A commercial multi-enzyme Natuzyme50® was supplemented at a rate of 0 (control), 0.25, 0.5, 0.75 and 1.00 g/kg DM feed in the best performing diet (KLM 25). These diets were tested in Oreochromis mossambicus. Natuzyme50® supplementation led to improved growth performance. Fish fed the diet containing 0.50 g/kg had the best growth performance and protein ADC and highest levels of digestive enzyme activities. At higher (>0.50 g/kg) enzyme supplementation levels, growth performance decreased. The improved growth performance with enzyme supplementation was attributed to the presence of enzymes such as cellulase and xylanase in the cocktail that are not naturally produced by fish. In addition, the activities of endogenous enzymes were enhanced. The optimal Natuzyme50® dietary level for optimal growth performance in Oreochromis mossambicus was 0.62 g/kg DM feed.

The role of the lipid-soluble antioxidant α-tocopherol (vitamin E) in the nutrition of African catfish (Clarias gariepinus Burchell) has been investigated with respect to effects on growth, certain indices of health and prevention of tissue lipid peroxidation. Although juvenile C. gariepinus were not found to show an immediate dependency on vitamin E for growth, even during rapid growth stages, a minimum requirement of α-tocopherol based on the prevention of hepatic lipid peroxidation was established at 30-40 mg α-tocopherol per kg dry diet. This is in line with published values for numerous cultured fish species. Tissue α-tocopherol accretion was found to be dependent on dietary dose of the vitamin (supplied as all-rac-α-tocopheryl acetate) and, with the exception of blood-plasma, increased tissue tocopherol status resulted in increased stability against lipid peroxidation. Assessment of iron-ascorbate induced peroxidation (as TBARS) revealed that feeding catfish with diets containing a-tocopherol at several times the currently supplemented level, improved the stability of catfish muscle and this has fillet quality implications. Similarly, heightened fillet vitamin E content resulted in lower moisture exudation from previously frozen fillets, thus demonstrating the role of a-tocopherol in the maintenance of membrane integrity. Oxidation of dietary oils and elevated ingestion of iron were found to be antagonistic of tissue vitamin E concentration. Consumption of feed containing rancid oil had marked effects on tissue fatty acid composition and these effects were modulated by increased intake of α-tocopheryl acetate. In catfish fed diets containing similar amounts of ascorbate, a higher α-tocopherol supplement marginally improved ascorbate retention indicating a possible sparing of vitamin C by vitamin E. The present work will contribute significantly to the understanding of antioxidant nutrition in this poorly researched cultured species. Furthermore, these investigations have improved and strengthened the database of knowledge accumulated within the field of nutrition of finfish.

Invasive species are of particular concern as they have the potential to alter community structure and food web relationships within their invaded habitats. African sharptooth catfish Clarias gariepinus, a generalist predator, was introduced through an inter-basin water transfer scheme into the Great Fish and Sundays Rivers, Eastern Cape, South Africa, where it threatens the native riverine biota. This thesis assessed its impact from a trophic perspective. Patterns in catfish distribution and abundance revealed an upstream to downstream gradient that was associated with spatial distribution of most species within the mainstream, and a mainstream to tributary gradient that was associated with the spatial distribution of native minnows. The catfish was predicted to occur widely within the mainstem habitats and to decrease progressively along the mainstrem to tributary gradient with the physico-chemical environment being a good proxy for predicting both its occurrence and abundance. The results suggest the catfish proliferated within mainstem habitats where invasion resistance was possibly reduced due to alteration of flow. Population dynamics and size structuring of two native cyprinid minnows Pseudobarbus afer and Barbus anoplus, threatened by catfish, were examined within uninvaded headwater streams in relation to their proximate physical habitats. Their habitats were characterised by seasonal variation in physico-chemical conditions and a spatial variation in substrata compositions. No evidence of differences was found between seasons for density and capture probability for either species. The population size and density for P. afer was found to increase with increasing proportion of boulders. In comparison, B. anoplus population size and probability of capture increased with increasing proportion of bedrock and bank vegetation, respectively. Size structuring was explained predominantly by seasonality and habitat variables for P. afer and B. anoplus, respectively. Stable isotope ratios of carbon and nitrogen were used to compare the spatial variation in both the community-wide and catfish-specific niches and to estimate catfish prey sources from different habitats within the invaded systems. Aquatic community and catfish niches were statistically different among localities, suggesting that each locality had a distinct community-wide trophic structure. Dispersion metrics indicated no evidence of differences in the clustering among individuals, but provided evidence of differences in path trajectories for the comparisons of catfish populations that suggested dietary plasticity within different localities. Dietary studies revealed both ontogenetic shift and omnivory that suggested that catfish may exhibit less pronounced top-down effects within its invaded habitats. Manipulative experiments were used to test the response of benthic macroinvertebrates within two rivers that were differentially impacted by catfish as a presstype disturbance. Macroinvertebrates were non-responsive to catfish presence within a system where catfish had previously been established. In contrast, excluding catfish in this system indicated a response that suggested the importance of refuge within invaded habitats and the possible recovery pattern of certain macroinvertebrate taxa. By comparison, introduction of catfish within previously uninvaded localities provided evidence of direct catfish impact through elimination of conspicuous taxa. Acoustic telemetry was used to investigate catfish movement patterns within an invaded lentic habitat and provided evidence that habitat utilisation was non-random. The shallow and structured river mouth habitat, which was most utilised, was probably the most ideal for its breeding and feeding. This inferred potential overlap with native species and suggested the risk of predation and competitive interference. Catfish also exhibited both nocturnal and diurnal activity patterns that were probably related to feeding.

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Financiadora de Estudos e Projetos
Air-breathing fish are classified as obligatory (when breathing obligatory atmospheric air independently of the water O2 tension) or facultative air-breather (using an air breathing organ ABO -, when theirs gills are not able to extract all O2 necessary to maintain the aerobic mechanisms under hypoxic conditions). The catfish, Clarias gariepinus, is airbreathing fish that shows modifications on the gill lamella, forming a ventilatory fan, and on the 2o e 4o gill arches, forming an arborescent organ. These structures form the ABO of this specie.The objectives of the present study were: 1. To determine if C. gariepinus is an obligatory or a facultative air breather. 2. To analyze the cardio-respiratory responses ( VO2 - metabolic rate; VG - gill ventilation; VT ventilatory volume; fR respiratory frequency; EO2 O2 extraction from the ventilatory current; fH- heart frequency) in response to progressive hypoxia. 3. To verify if the critical O2 tension (PcO2) of this specie is correlated with the O2 uptake from the atmospheric air.To classify the air-breathing mode of C. Gariepinus, the fish (Wt ~ 350 g; n = 7) were maintained in normoxia during 24 hours without access to air. The fR maintained constant during all the experiment and there was no mortality, indicating that C. gariepinus is a facultative air-breather. To analyze the cardio-respiratory responses to progressive hypoxia, VO2 , EO2, fR, VT, VG , EO2 and fH were recorded under the following water O2 tensions(PwO2): 100, 70, 50 e 30 mmHg. Fish maintained a constant VO2 until the PcO2 (~ 55 mmHg), below which VO2 decreased significantly. This decreasing was followed with the significant reduction of EO2 in PinspO2 of 62,7 ± 1,30 mmHg reaching values of 19,6 ± 1,9 % in severe hypoxia. The VG and the VT increased progressively until PinspO2 of 28,0 ± 0,5 mmHg, reaching highest values of, respectively, 1545,7 ± 63,5 mLH2O.kg-1.min-1, 33,9 ± 0,8 mLH2O.Kg-1.resp-1 e 57,2 ± 1,4 resp.min-1. The fH reduced progressively from 43,4 ± 0,4 bpm, in normóxia, arriving significant values just above the PcO2 and reaching minimum values (19,2 ± 3,0 bpm) in severe hypoxia. Under progressive hypoxia (100, 70, 50, 30 e 20 mmHg) and with the access to the atmospheric air, C. gariepinus (Wt ~ 610 g; n = 9) presented a 5-fold increase in the air-breathing frequency (fRA). A bradycardia was observed just before the air breath and a tachycardia just after.Concluding, C. gariepinus is a continuous facultative air-breathing fish that regulate the 2 O V until the PcO2 of ~54 mmHg. Below this tension fish increase the VG mainly due to a larger increase of VT (lower metabolic cost of VG ). The hypoxic pre-air breath bradycardia is characteristic of aquatic breathers while the post-air breath tachycardia is typical of air respirators. The fRA increased proportionally with the progressive hypoxia, mainly just above the PcO2. These results show that C. gariepinus is adapted to survive at hypoxic habitats and that this species show a higher dependence of the atmospheric air than the others facultative air-breathing fishes.
Peixes de respiração aérea são classificados como respiradores aéreos obrigatórios (aqueles que respiram ar atmosférico independente das tensões de O2 da água) ou facultativos (aqueles que usam o órgão de respiração aérea ABO quando as brânquias não conseguem extrair a quantidade de O2 necessário para manter o metabolismo aeróbico em condições hipóxicas). O bagre-africano, Clarias gariepinus, é um peixe de respiração aérea que apresenta modificações na lamela branquial, formando um leque ventilatório, e, nos 2os e 4os arcos branquiais, os órgãos arborescentes. Estas últimas estruturas formam o ABO desta espécie.Os objetivos do presente estudo foram: 1. Determinar se C. gariepinus é um respirador aéreo facultativo ou obrigatório. 2. Analisar as respostas cardiorrespiratórias ( VO2 - taxa metabólica; EO2 - extração de O2 da corrente ventilatória; VG - ventilação branquial; VT - volume ventilatório; fR - frequência respiratória; fH- frequência cardíaca) em resposta a hipóxia gradual. 3. Verificar se a tensão crítica de O2 (PcO2) desta espécie está relacionada com a tomada de O2 do ar atmosférico.Para classificar a modalidade da respiração aérea de C. gariepinus, os peixes (Wt ~ 350 g; n = 7) foram mantidos em normóxia durante 24 h sem acesso ao ar atmosférico. A fR manteve-se constante durante todo o experimento e não houve mortalidade, indicando que C. gariepinus é um respirador aéreo facultativo. Para analisar as respostas cardiorrespiratórias em normóxia (controle) e hipóxia gradual, a VO2 , EO2, fR, VT, V G e fH foram registradas durante as seguintes tensões de O2 (PwO2): 100, 70, 50 e 30 mmHg. Os peixes mantiveram VO2 constante até a PcO2 (~ 55 mmHg), abaixo da qual a VO2 decresceu significativamente. Esta diminuição da VO2 foi acompanhada da diminuição significativa da EO2 em PinspO2 de 62,7 ± 1,30 mmHg atingindo valores de 19,6 ± 1,9 %, em hipóxia severa. A VG , VT e fR aumentaram progressivamente até a PinspO2 de 28,0 ± 0,5 mmHg, chegando a valores máximos de, respectivamente, 1545,7 ± 63,5 mLH2O.kg-1.min-1, 33,9 ± 0,8 mLH2O.Kg-1.resp-1 e 57,2 ± 1,4 resp.min-1. A fH diminui progressivamente de 43,4 ± 0,4 bpm, em normóxia, até alcançar valores significativos próximos a PcO2 e valores mínimos em hipóxia severa (19,2 ± 3,0 bpm). Em experimentos de hipóxia gradual (100, 70, 50, 30, 20 e 10 mmHg) com acesso ao ar atmosférico, C. gariepinus aumentou aproximadamente 5x a frequência de respiração aérea (fRA). Em cada tensão hipóxica ocorreu uma bradicardia pré-RA seguido de taquicardia significativa pós-RA (típico de respiração aérea); a fR manteve-se praticamente constante (~ 32 resp.min-1) até as duas últimas PwO2 (20 e 10 mmHg), nas quais a fR diminuiu para 23,0 ± 1,18 resp.min-1.Finalmente, C. gariepinus é um peixe de respiração aérea facultativa contínua que regula a VO2 até a PcO2 de ~ 55 mmHg. Abaixo desta tensão o animal aumenta a VG devido principalmente a um pronunciado aumento na VT (diminuição do custo metabólico da VG ). A bradicardia hipóxica pré-RA é uma característica de respiradores aquáticos, enquanto a taquicardia hipóxica pós-RA é típica de respiradores aéreos. A fRA aumentou proporcionalmente com a hipóxia gradual, principalmente próximo a PcO2. Tais resultados demonstram que C. gariepinus está adaptado a sobreviver em habitats hipóxicos e demonstra uma maior dependência do ar atmosférico do que outros respiradores bimodais facultativos.

Thesis (M. Sc. (Agriculture)) -- University of Limpopo, 2016
Fish assemblages in relation to environmental variables within the Broederstroom and Debengeni Rivers were investigated. Both rivers were characterized by coarse substrates (pebble and gravel), temperatures below 20°C and moderate depth. Trout dominated fish assemblages in terms of numbers caught and was only distributed at higher altitude sites >1400 m (a.s.l). Coarse substrates, temperatures below 15°C, flow rate, depth and riparian cover were the variables shown important for the distribution of trout by multivariate analysis. The confinement of the trout to higher altitude and lack of optimal habitat variables at lower altitude sites contributed to the assertion that the area is marginal for trout distribution. It was therefore inferred that the marginality of the area is the possible explanation for trout failure to self-sustain its population, therefore dependent on the continuous restocks by the local hatchery. The continuous restocks of small size trout in the Broederstroom River prompted a subsequent study where trout’s impact on macroinvertebrate communities was evaluated through surveys and field experiments. The ability of small trout to utilize macroinvertebrates made them suitable candidates to evaluating their impact in the area. Aquatic invertebrates were found to be the main food source for the trout in the area. Taxa such as Gomphidae and Potamonautidae were the most frequent food items from the analyzed stomachs of trout. However, observations from both field surveys and experiments showed that trout is a weak regulator of macroinvertebrate diversity in the area, since there were no significant differences (ANOVA, P<0.05) in the diversity of invertebrates from trout invaded and uninvaded sites. Trout being a weak regulator of macroinvertebrate diversity in the area, it prompted surveys to the Ebenezer Dam to determine its competitive interactions with native predatory species. If the introduced species is a more efficient predator than the native predator species, it may affect changes in the structure of the habitat and food resource. Trout in the Ebenezer Dam was found to be selective to habitat variables whilst C. gariepinus was cosmopolitan to all habitat categories. The catfish also had a broader food preference than trout and the diversity of the food items was significantly different (ANOVA, P<0.05) between the two species. Unfortunately, the interspecific food overlap between trout and the catfish could not be determined in Ebenezer Dam, because of the small sample size of trout but food selection between vii them was evident. It was then concluded that the native catfish has a wider niche and it is a more efficient predator than the introduced trout. This observation contributed further to the assertion that the area is marginal for trout to thrive. Due to trout selection of habitat variables, it became prudent to carry out another study where the past climate and land use changes were analyzed to determine their effect on the habitat that could have affected the distribution of trout in the area. Future projections were also made to determine possible future impacts of climate change on the distribution of trout in the area. The effects of climate and land use change resulted in warmer water temperature, altered riparian cover and altered stream flow patterns. The changes could have influenced the confinement of trout to higher altitude catchments. The projected maximum temperatures by 2050 shows an increase from 2014 with a decline in precipitation. If these projections are to be the same for water temperature and flow regimes, coupled with current land uses in the area, they will continue to affect the distribution of trout negatively.

Fermented silage was prepared from a mixture of minced tiiapias (Oreochromis spp. ), different carbohydrate substrates (molasses, corn flour, tapioca flour) and Lactobacillus plantarum as inoculum, incubated anaerobically for 30 days at 5°-35°C. The pH and protein solubilization were temperature-dependent, and the source of carbohydrate substrate did not affect non-protein nitrogen (NPN) content or proximate composition of tilapla silage. During storage at 30°C for 180 days, NPN content increased and there was 8-11% loss of tryptophan. Moist diets containing tilapla silage (stored up to 60 days) were fed to Clarias gariepinus and differences in growth and protein utilization were demonstrated, but there were no effects on body composition. Partial replacement of fish meal with co-dried tilapla silage and soybean flour blend (FSS: BF) in dry diets supported growth and protein utilization similar to the control treatment. Fish growth and protein utilization were reduced with total replacement of fish meal. Apparent protein digestibility decreased with Increasing dietary level of co-dried FSS: BF. Carcass composition was not affected and morphological defects were not observed. Co-dried tilapla silage blended with soybean meal, poultry by-product meal, hydrolysed feather meal or meat and bone meal (FSS: BM, FSP: BM, FSH: FM, FSM: BM) (providing 50% of the dietary protein) In dry diets fed to Oreochromis niloticus and Clarias gariepinus gave differences In growth, protein utilization and digestibility, and apparent energy digestibility. Carcass composition was not affected by silage blend and histological examination of exocrine pancreas, liver and Intestine tissues did not show any lesions suggestive of nutritional imbalance. Haematocrit, haemoglobin content and mean cell haemoglobin concentration values showed no differences among the treatments. The results indicated that fermented tilapla silage is a suitable protein supplement in moist or dry diets for Oreochromis niloticus and Clarias gariepinus, without affecting feed efficiency, fish growth or health.

Colonisation theory relative to introduced populations was examined with a view to determining the usefulness of theoretical concepts in the prediction of the success of an invasion by a species. To this end, the Great Fish River, with reference to species introduced by the Orange/Fish Tunnel, was used as a case history. It was concluded that theoretical descriptions of population growth, control and decline are useful only when considering individual ecosystems or species. The highly variable nature of species and environments nullifies attempts to simplify behavioural characteristics into a predictive framework. There is an abundance of terminology associated with introduced organisms and frequently many of these terms are used synonymously. Eleven terms have been defined in this thesis with a view to standardising terminology. Characteristics of species and environments which enhance their susceptibility to invasions by exotic ichthyofauna were discussed and summarised. Distribution data concerning exotic fish introduced into the Great Fish River by the Orange/Fish Tunnel has demonstrated that, with the exception of Clarias gariepinus, all remaining exotics have restricted distributions. Only Barbus aeneus appears to be extending its range down the drainage. Age, Growth, reproduction and condition data support the conclusion that, excluding B. aeneus and C. gariepinus, invasive species in the drainage are not performing well. Of the five invasive species (B. aeneus, Labeo capensis, L. umbratus, Gephyroglanis sclateri and Cyprinus carpio), only two have established populations (B. aeneus· and C. gariepinus). Labeo umbratus and C. carpio were present on the Great Fish River prior to the construction of the tunnel and populations of the species could not be distinguished. It was concluded that there is no evidence to suggest that exotic species introduced into the Great Fish River are having a deleterious effect on indigenous, endangered ichthyofauna. Monitoring of the drainage should be continued to ensure that a danger to indigenous species does not develop.

A carne mecanicamente separada (CMS) de pescado é um produto obtido a partir de uma única espécie, ou mistura de espécies de peixes através do processo de separação mecanizada da parte comestível. O bagre africano (Clarias gariepinus) é produzido principalmente nos países africanos e europeus e recentemente foi introduzido na Índia, China e Brasil, destinados exclusivamente ao consumo. O objetivo deste trabalho foi obter e caracterizar a CMS de bagre africano e avaliar sua estabilidade durante o armazenamento a -18°C. Foi determinado o rendimento do processo de obtenção da CMS e a estabilidade foi acompanhada por seis meses com relação a aspectos microbiológicos e físico-químicos (TBARS, BVT, pH e drip), de três tratamentos (A - CMS sem lavar, B - CMS com uma lavagem e C - CMS com duas lavagens). No início e após 90 e 180 dias de armazenamento sob congelamento, as CMS foram utilizadas para elaboração de fishburgers, os quais foram avaliados microbiológica e sensorialmente. A lavagem promoveu mudanças na composição centesimal da CMS, principalmente o aumento do teor de umidade e diminuição dos teores de proteína bruta. Durante o período de estocagem, as CMS mantiveram-se estáveis independentemente da lavagem. Foi observado rendimento da CMS, de aproximadamente 50% em relação ao peixe inteiro. A CMS com duas lavagens apresentou maior umidade (84,26%) que as CMS com uma lavagem (78,52%) e sem lavar (78,42%), ocorrendo também perda de proteína, lipídeos e cinzas, pela lixiviação desses compostos. Os teores de BVT mantiveram-se estáveis durante o período de armazenamento diferindo apenas entre os tratamentos, sendo que a CMS sem lavar apresentou maior valor médio (15,79 mg BVT/100g) que as CMS com uma (5,46 mg BVT/100g) e duas lavagens (2,61mg/100g). No dia zero, o maior valor de TBARS foi encontrado na CMS sem lavar (0,216 mg malonaldeído/kg), ao passo que nas CMS com 1 e 2 lavagens os valores foram respectivamente de 0,083 e 0,099 mg malonaldeído/kg, indicando que a lavagem causou lixiviação da maior parte dos compostos responsáveis pela oxidação lipídica. A legislação brasileira não indica um limite de oxidação lipídica avaliado pelo método de TBARS para CMS de pescado, porém os valores encontrados no final do período de estocagem (0,405; 0,511 e 0,420 mg malonaldeído/kg) para as CMS sem lavar, com 1 e 2 lavagens respectivamente são baixos e indicam pouca oxidação. Os parâmetros microbiológicos da CMS e do fishburger se mantiveram de acordo com a legislação brasileira. Os fishburgers foram muito bem aceitos pelos provadores e o fishburger elaborado com CMS com uma lavagem foi melhor avaliado quanto à aceitação global. As pequenas alterações ocorridas durante o período de armazenamento não afetaram a qualidade da CMS, indicando viabilidade para formulação de produtos com CMS estocada congelada por 180 dias. O processamento de bagre africano na forma de CMS pode ser uma alternativa para aproveitamento de uma espécie sub-utilizada, gerando produtos da piscicultura com valor agregado.
Minced fish (CMS) is a product obtained from only or sereral fish species through the mechanical separation of edible section. African catfish is produced mainly in African and european countries and recently was introduced in India, China and Brazil, destined exclusively to comsumption. The aim of the present study was obtain and characterize the african catfish minced and evaluate the stability during the period of storage under -18°C. Minced fish process yield was determinated and the stability was measured for six months concerning microbiological and physico-chemical analysis (TBARS, BVT, pH and drip), from three treatments (A CMS unwashed, B CMS washed once and C CMS washed twice). The beginning and after 90 and 180 days of frozen storage, the CMS was utilized for preparation of fishburger, that was evaluated for microbiological and sensorial analysis. The CMS washing process promoted changes in centesimal composition, mainly the increase of the moisture and decrease of total protein. During the storage period, the CMS kept the stability apart of washing process. The minced fish process yield was approximately 50% respecting whole fish. The CMS washed twice showed higher moisture (84,26%) than the CMS washed once (78,52%) and CMS unwashed (78,42%), occuring waste of protein, lipid and ash, by washing. During the storage, the BVT kept stable, disagree between the treatments, and the CMS unwashed exhibit higher mean value (15,79 mg BVT/100g) than CMS washed once (5,46 mg BVT/100g) and CMS washed twice (2,61mg/100g). At the zero day, the bigger value of TBARS was determinated in CMS unwashed (0,216 mg malonaldeído/kg), but in CMS washed once and twice, the values was 0,083 e 0,099 mg malonaldeído/kg respectively, signify that the washing process induced removal the majority part of compounds responsible by the lipidic oxidation. The Brazilian legislation do not indicate a limit of CMS lipid oxidation evaluated by TBARS method, however the values at the end of the storage (0,405; 0,511 e 0,420 mg malonaldeído/kg) for CMS without, with one and with two washing are low and indicate low oxidation. The CMS and the fishburger microbiological parameters kept agreed with Brazilian legislation. The fishburgers was accepted by the samplers and the fishburger elaborated with CMS washed once was better evaluated to general acceptability. The changes occured during the period of storage have not affect on CMS quality, indicating availability to products formulated by CMS with 180 days of frozen storage. The CMS process of african catfish can be a alternative to employment of a specie under-utilized, creating aquaculture products with aggregated value.

Endocrine disrupting chemicals (EDCs) such as DDT have the ability to disrupt hormonally controlled processes, such as spermatogenesis, which is the maturation of germ cells into spermatozoa. During normal spermatogenesis, germ cell apoptosis can occur, but the degree of apoptosis within the testis could possibly be affected by exposure to EDCs. In 2004, a pilot study on the reproductive health of two freshwater fish species, Oreochromis mossambicus and Clarias gariepinus, from three impoundments in the Luvuvhu River, found concerning levels of DDT and its metabolites in both species from the Nandoni Dam, and in O. mossambicus from the Xikundu Weir. This was not surprising as a large part of the Luvuvhu River catchment is located within an area where ongoing DDT-spraying occurs for vector control purposes. Hence, in 2006, a larger WRC-funded project began to further investigate the findings from the pilot study. A subsidiary study, spanning two seasons, was initiated to investigate testicular apoptosis in fish from the polluted systems, the Nandoni Dam (ND) and the Xikundu Weir (XW), as well as a reference site, the Albasini Dam (AD), utilizing caspase-3 and TUNEL immunoexpression as apoptotic markers. In addition, three fixatives, Bouin’s Fluid (BF), Neutrally Buffered Formalin (NBF) and Paraformaldehyde (PFA), were used to determine which would be the optimal fixative for both histological and immunohistochemical assessments. Sampling occurred during season 1, the low-flow season (October 2007), during DDT spraying of the surrounding area, and season 2, the high–flow season (February 2008), two months after the DDT-spraying was completed. The testes of O. mossambicus (n = 19 season 1, n = 25 season 2) and C. gariepinus (n = 19 season 1, n = 20 season 2) were fixed in the above-mentioned fixatives, embedded in paraffin wax, prepared for immunohistochemistry, and exposed to caspase-3 antibodies and TUNEL antibodies individually. The results indicated that the residues of p,p´-DDT - DDD and - DDE were found in the fat samples of both O. mossambicus and C. gariepinus, in AD, ND and XW. Testicular apoptotic assessment using the caspase-3 assay clearly labeled spermatocytes in the process of cellular death in both seasons, in all three fixatives. When comparing the two assays, a significant difference is found between the caspase-3 and TUNEL positive cells. The results further show that, when comparing the three sampling sites, the highest amount of positive cells are found at the XW. The decrease observed in season two, in both the caspase-3 and TUNEL assay may possibly be linked to the stage of spermatogenesis, coinciding with hormonal changes associated with the different sampling seasons (i.e. breeding and non-breeding seasons). The levels of DDT found in the fat tissue, could not be correlated to an up-regulation in apoptotic cells. The results The results indicated that the choice of fixative, could affect the identification of the amount of positive cells. The utility of the caspase-3 and TUNEL assays, in conjunction with all three fixatives, proves a successful tool in assessing and quantifying modulated testicular apoptosis, creating greater research potential in the assessment of the effects of aquatic pollution. Copyright
Dissertation (MSc)--University of Pretoria, 2008.
Physiology
unrestricted

The Rietvlei Dam near Pretoria, South Africa, provides drinking water for the city and for the wild life in the Rietvlei Nature Reserve, and is also used for recreational fishing. The dam is part of the Sesmyl Spruit system, which has a history of pollution, the major sources of which are industrial, agricultural and sewage from informal human settlements upstream of the reserve. With a large wetland separating the upstream Marais Dam and the Rietvlei Dam, the system has a high conservation priority status because of the high number of bird species that breed and roost in the various habitats. As part of a big aquatic health project in the Zoology Department, Rand Afrikaans University, aimed at finding suitable biomarkers for water quality monitoring in the system, this study was done to identify the major internal helminth parasites of the sharptooth catfish, Clarias gariepinus, that can be used in fish health assessment studies, and to determine their prevalence and intensity in the Rietvlei Dam. Fish were collected during one sampling survey and examined for endoparasites, also noting any ectoparasites that are recorded in routine fish health studies. Five species of helminths were identified: the adult cestodes, Polyonchobothrium clarias (intestine and stomach), Proteocephalus glanduliger (anterior intestine), the adult nematode Procamallanus laevionchus (stomach), larvae of the nematode Contracaecum sp. and many trematode metacercariae encysted in the muscles, of which only Ornithodiplostomum sp. was successfully excysted and identified. This trematode is recorded in South Africa for the first time, but could not be specifically identified because the reproductive system was still immature. Examination of piscivorous birds in the area or experimental infection of young birds are the only means by which the adult trematodes can be obtained. The adult cestodes and nematodes had specialised structures for attachment to the stomach and/or intestinal mucosa, adaptations associated with pathological effects in the host. Polyonchobothrium clarias had a crown of 26-30 hooks on its rostellum, and this number differs from those of specimens described from catfish in other African countries. Scanning electron microscopy showed that the rostellum of the P. clarias specimens from Rietvlei Dam was different from that of specimens from other localities in South Africa. Proteocephalus glanduliger in C. gariepinus from Rietvlei Dam differed in strobila size and size of glandular organ from specimens described by Janicki (Egypt) and Mashego (South Africa), the present specimens being much longer but with smaller glandular organs. Procamallanus laevionchus is a common parasite of catfish from many African countries, including South Africa, and scanning electron microscopy showed some form of transverse markings and presence of papillae-like structures at the posterior end of female specimens, an observation which was not described in previous studies. Larval Contracaecum are also common in C. gariepinus and other fish species, and adults have been identified in several species of fish-eating birds from South Africa. The sample size of fish collected in this survey was too low for a full health assessment index (HAI) study to be undertaken. Polyonchobothrium clarias and Contracaecum, however, were highly prevalent in the host species, and Contracaecum and Ornithodiplostomum occurred at high intensity (up to 44 and 140 respectively). Endoparasites of C. gariepinus can therefore be used in the fish HAI as a bioindicator of water quality. Only two ectoparasitic species were found on C. gariepinus: Argulus japonicus (skin and fins) and Lamproglena clariae (gills). Most water quality variables from the dam were within the target limits recommended by the Department of Water Affairs and Forestry, but the levels of inorganic nitrogen (nitrate and ammonia) and phosphorus (orthophosphate) exceeded the limit. If uncontrolled, these may lead to eutrophication of the dam. With the parasite species and diversity known, it is recommended that fish health assessments should be conducted along pollution gradients in the system to determine whether it can be incorporated into the suite of biomarkers for water quality monitoring of the Sesmyl Spruit system.
Prof. A. Avent-Oldewage

M.Sc. (Zoology)
The freshwater indicator fish species, Clarias gariepinus, was used to assess and compare the health status of fish from the Hartbeespoort Dam (HBPD) and the Groot Marico Bosveld Dam (GM) which was used as a reference site. HBPD is known to be polluted and renowned for its extreme eutrophic state. GM receives water from the Marico River and is said to be in an unmodified natural ecological state. Adult Clarias gariepinus were sampled using gill nets; during low-flow (n=17) and high-flow (n=20) seasons from the HBPD, and once from the GM (n = 20). A histology-based fish health assessment was done using a necropsy based health assessment index and a qualitative and semi-quantitative histological assessment on selected target organs namely the gills, liver, kidney and gonads. Focus was also placed on reproductive health aspects by staging the gonads according to their reproductive development and assessing the motility of activated sperm using computer assisted sperm analysis (CASA). Water samples were analyzed for selected physical parameters and for selected metals. The results showed distinct macroscopic differences in the livers and testes comparing the two sites. Fish from HBPD had fatty livers and the macroscopic morphology of the testes showed abnormalities regarding the interstitial tissue, possibly due to the proliferation of connective tissue. The macroscopic abnormalities of the livers were reflected in the histological assessment, which concluded steatosis, vacuolation, hepatocyte nuclear alterations and the presence of large numbers of melanomacrophage centers (MMCs). Of these alterations, only MMCs and intracellular deposits were found in fish from the GM. When comparing the HBPD low-flow (LF) and high-flow (HF) sampling trips, the fish from the low-flow had more alterations present in all organs. While the CASA results showed that the motility, velocity and progression of sperm were lower in fish from the HBPD for all parameters, results from GM showed the ideal trend expected from the moment of sperm activation until degeneration. The velocity and progression were significantly (p value <0.05) different between HBPD samples and fish from the GM. The water quality showed increased concentrations of selenium, as well as the endocrine disrupting chemicals (EDCs) nonylphenol and di-n-butyl phthalate. According to the selected parameters assessed, it seems like the water of the HBPD has increasing detriment upon fish health.

M.Sc.
The Vaal Dam subcatchment is located in the upper reaches of the Vaal River. As a result the water quality is reasonably good. In contrast the Vaal River Barrage catchment includes the PWV area, resulting in poorer water quality. During this study, a fish Health Assessment Index (HAI) successfully tested in previous studies on the Olifants River System was applied to the Vaal River System. The aim was to determine if the HAI could distinguish between the Vaal Dam and Vaal River Barrage with regards to water quality. Surveys were conducted bimonthly from November 1998 to February 2000. Physical water quality variables were measured. Water and sediment samples were also collected and analyzed (Institute for Water Quality Studies, Department of Water Affairs and Forestry) to verify the HAI results. Rand Water Board and the Department of Water Affairs and Forestry also made water quality data available. Twenty sharptooth catfish, Clarias gariepinus, were collected from both localities with the aid of gill nets. Fish were checked for external parasites on the boat. On land fish were weighed and measured, after which blood was drawn and slime smears made. Blood and slime smears were examined under a light microscope for parasites. The HAI examination was performed after severing the spinal cord. Internal parasite numbers were recorded. From the parasite data collected infestation statistics were calculated. Four variations of the Parasite Index (PI) were incorporated in the HAI and results compared. During each survey gill arch, gill filament, muscle, skin and liver tissues were collected from each fish. These were analyzed for strontium, aluminium, chromium, manganese, iron, lead, copper, zinc and nickel concentrations using atomic absorption spectrophotometry. Differences in water and sediment trace metal concentrations between localities were small. Metal concentrations in fish tissues recorded from both localities were also almost identical. Possible explanations for this trend were discussed in the relevant section. Highest metal concentrations were generally recorded in gill tissue followed by liver, skin and muscle. Physical water quality variables (salinity and conductivity), and macro water analysis (e.g. phosphate and nitrate) indicated that water quality at the Vaal River Barrage was poorer. The HAI confirmed this. Higher index values were recorded from the Vaal River Barrage, with the converse being true for the Vaal Dam. Regression analysis indicated that plasma protein, haematocrit and the index value obtained using the Inverted Parasite Index, most successfully predicted (70 %) from where a randomly chosen fish were collected. When viewing index values obtained using the four versions of the PI, all four distinguished between localities. The discriminatory ability of the Inverted PI was slightly higher than that of the other PI's. It is concluded that the HAI distinguished successfully between the Vaal Dam and Vaal River Barrage on the grounds of water quality. Poor fish health correlated with decreasing water quality (salinity and eutrophication).

M.Sc. (Aquatic Health)
South Africa’s freshwater ecosystems are under threat due to anthropogenic activities. Recent reports have shown that the Hartbeespoort- (HBPD), Klipvoor- (KD) and Bospoort Dam (BD) impoundments situated in the North-West Province are polluted as a result of mining, industrial and agricultural activities. These impoundments are classified as being in a hypertrophic state. The health status of fish in these impoundments is of concern, and needs to be investigated. For this purpose, Clarias gariepinus and Cyprinus carpio were collected for a histology-based fish health assessment. These two species are present in the selected dams and are some of the preferred fish species for human consumption by the local people. The aim of the study was to determine the health status of these fish species in HPBD, KD and BD using a semi-quantitative histopathological assessment on selected target organs and compare the results to fish from a reference site, the Marico-Bosveld Dam (MBD). Gill nets were used for the collection of specimens. Fish were macroscopically examined, weighed and measured for the calculation of the condition factor. Blood samples were collected for haematocrit, leukocrit and total protein determination. Once sacrificed, a necropsy-based health assessment (HAI) was performed to determine any abnormalities within the visceral cavity. The selected target organs were excised and weighed for the calculation of selected biometric indices. Collected tissue samples were processed using standard histological techniques and the prepared slides were stained using Haematoxylin and Eosin. Macroscopically, a number of fish from polluted sites exhibited liver with fatty change and focal discoloration as well as severe parasites within the visceral cavity. As a result, higher HAI values were recorded in polluted sites compared to the reference site. The haematocrit values varied from normal to below and above the normal range. Leukocrit values were within the normal range except for C. gariepinus from HBPD, which was above the normal range. Total protein values were within the normal range for both species for all sites. The condition factor and hepatosomatic index (HSI) values were within the accepted range except for the HSI of C. gariepinus from MBD. The mean organ index for all study sites fell within class 1 with the exception of the liver index from HBPD, KD and BD which was in class 2. Class 1 (index value <10) is indicative of slight histological alterations while class 2 (index value 10-25) translates to moderate histological alterations. Overall, a higher prevalence of histopathological alterations was noted among fish from polluted sites compared to fish from the reference site. Hence, on the basis of the macroscopic and histopathological results, the fish from the polluted sites were more affected in terms of these parameters compared to fish from the reference site. The results therefore provide valuable information for future bio-monitoring studies in the HBPD, KD and BD impoundments.

Ph.D.
The current study evaluated a bio-monitoring technique developed in the USA by Adams, Brown and Goede, 1993. This project was sponsored by the Department of Water Affairs and Forestry (DWAF), to enable testing of the Health Assessment Index (HAI) under South African conditions. Testing took place in the Olifants River system, one of the most polluted river systems . in South Africa. Initially two river points were tested using Oreochromis mossambicus (Robinson, 1996), Clarias gariepinus (Marx, 1996) and Labeo rosae (Luus-Powell, 1997). The current study re-tested the HAI at the same two sample sites, namely Mamba and Balule in the Kruger National Park, using 0. mossambicus and C. gariepinus respectively. Two additional sites were tested in the upper catchment area, namely Loskop Dam and Bronkhorstspruit Dam. The current study further enabled the comparison of HAI results collected during drought and flood conditions. Results obtained after deployment of the HAI were corroborated using chemical analysis of water, sediment and biota. Water and sediment analysis was carried out by the Institute for Water Quality Studies using standard techniques. Bio-accumulation of aluminium, copper, iron, lead, manganese, nickel, strontium and zinc was assessed in the gills, liver, skin and muscle tissue of sample fish using standard Atomic Absorption Spectrometry techniques. Modifications made to the original HAI involved the inclusion of variable ranking in the assessment of fish parasites, with endo- and ectoparasites evaluated separately. Testing of this parasite hypothesis lead to the development of a Parasite Index component to the HAI. Assessment of water, sediment and fish tissue determined that the Olifants River system is indeed exposed to macro and heavy metal pollutants, which negatively affect aquatic health. Constituents posing the greatest threat are chlorides, fluorides, phosphates, total dissolved solids, copper and iron concentrations. Testing the HAI and parasite hypothesis using C. gariepinus, provided the most meaningful results. During testing of the parasite hypothesis both endo- and ectoparasite numbers conformed to the suggested idea that higher endoparasite numbers will occur at highly impacted areas, whereby ectoparasite numbers will be low. This was particularly evident in the lower catchment area, whereby comparisons between drought and flood conditions were carried out. Subsequent decreases in water quality directly after the flood were noted using water and sediment analysis. This observation reflects the results gathered using the HAT and during testing of the parasite hypothesis at all four sample sites. During statistical analysis of the HAI, using logistic regression analysis, parasite numbers, more specifically endoparasite numbers, were the most indicative of fish health. Environmental stressors (flood conditions) result in immunological responses observed in fish, and are reflected statistically using the HAI as changes in WBC %. It is suggested that endoparasites and WBC % provide the best overall assessment of fish condition. These variables should thus not be eliminated, in order to streamline the HAI evaluation procedures. Testing of this bio-monitoring technique under South African conditions provided meaningful results. This indicates that the HAI can be used to assess water quality, with existing water monitoring programmes further benefiting from its incorporation.

PhD
An important component of fish health is an optimally functioning reproductive system. The Luvuvhu River Catchment in the Limpopo Province, South Africa, is a tropical, high-risk malaria area where 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), an endocrine disrupting chemical (EDC), has been used annually since 1945 as a malaria vector control. DDT is known to affect testes morphology and motility of fish sperm. As such, testicular histology and sperm motility (kinematic) parameters were studied as reproductive indicators of the reproductive capacity for two wild, indigenous fish species (Oreochromis mossambicus and Clarias gariepinus) from the currently DDT sprayed area. Three field studies were carried out over two years (2007 – 2008), including two high flow (HF) periods and one low flow (LF) period [HF 1 (March 07), LF (October 07), HF 2 (February 08)]. Both species were sampled from three sites on the Luvuvhu River for testicular histology and computer assisted sperm analysis (CASA), during all three field studies. The sites included a reference site outside the DDT sprayed area, Albasini Dam (AD), and two exposed sites within the DDT sprayed area, Xikundu Weir (XW) and Nandoni Dam (ND). CASA, based on open-source software, was used for the first time in South Africa to assess sperm kinematic parameters of indigenous fish species in field conditions. These included percent motile sperm (% MOT), curvilinear velocity (VCL μm s-1), velocity of an average path (VAP μm s-1), straight line velocity (VSL μm s-1), linearity (LIN %), progression (PROG μm), and average efficiency (AVE. EFF.). Water and sediment samples were collected during all field studies from the three sites for metal and EDC analysis. Controlled laboratory studies were also carried out on the sperm of both species, externally sourced from aquaculture farms equipped to breed and raise fish in toxicant free water. The laboratory studies involved in vitro exposure of spermatozoa to two different, but environmentally relevant, concentrations of both DDT (DDT 1: 0.27 μg L-1; DDT 2: 0.5 μg L-1) and 1,1-dihloro-2,2-bis(p-chlorophenyl)ethylene (DDE) (DDE 1: 0.11 μg L-1; DDE 2: 1.0 μg L-1) with the aim to provide data to support the possible outcomes found in the field studies using CASA. Furthermore, peroxidation of sperm lipids was assayed by production of malondialdehyde (MDA) after in vitro exposure of spermatozoa to DDT and DDE. DDT and its metabolites were found in varying concentrations in the water from all three sites (0.1 μg L-1 – 1.2 μg L-1). Levels of dieldrin (3.5 μg L-1) and lindane (9.4 μg L-1) residues were also found at XW in HF 2. The histological results revealed alterations to testis tissue of both species at all three sites. The testes were assessed through the identification of alterations and an organ index was calculated: Testes Index (IT). The index is indicative of the histological response in the respective tissue type. O. mossambicus at XW had the highest mean IT value during LF (7.45 ± 5.73) and for all field studies combined (5.47 ± 4.63), primarily due to the occurrence of testicular oocytes (intersex), where the frequency of prevalence was 72.73% and 58.82% respectively. These results were statistically higher than the laboratory control (C) group. The CASA results showed statistical differences primarily for O. mossambicus, where motility parameters were lower at XW when compared to AD. Laboratory exposures found a decrease in sperm motility (% MOT) between the control (C) group and the DDT 1, DDE 1 and DDE 2 exposed groups for C. gariepinus. No significant differences were seen for lipid peroxidation (MDA). On the other hand, no significant differences were seen in CASA parameters between the control and exposed laboratory groups for O. mossambicus, but there was an increase in MDA production from the control to the DDT 1 exposure group.

Ph.D. (Zoology)
Histomorphology as a tool to assess the health status of five economically important fish species in the Okavango Delta Panhandle, Botswana the Okavango Delta, and an inland freshwater wetland of national and international importance was designated by the Ramsar Convention in 1996. This site is of global importance because of a wide diversity of fish species found in this freshwater ecosystem. The Okavango Delta is also one of the last 'near pristine' sites on the African continent and therefore serves as an ideal reference site to describe the normal histomorphology of selected organs in sentinel fish species which could be used as reference for future toxicological studies. The aim of this study was to assess the health status of five economically important fish species namely, Clarias gariepinus (Burchell, 1822), Clarias ngamensis (Castelnau, 1861), Serranochromis robustus jallae (Gunther, 1864), Serranochromis angusticeps (Boulenger, 1907) and Hydrocynus vittatus (Castelnau, 1861) sampled from the Okavango Delta Panhandle, by describing the normal histomorphology of the liver, gills and gonads of the sentinel species. The sentinel fish species are of significant importance because they form an integral part of the small-scale commercial, subsistence and recreational fisheries in this ecosystem. In the past few decades, fish-health research has focused almost exclusively on histopathological alterations resulting from pollution caused by exposure to chemicals, parasitesand pathogens. Limited attention has been devoted to the normal histomorphology and health status of fish species in various aquatic ecosystems including the Okavango Delta Panhandle. Also, histopathological evaluations noted only the presence of abnormalities without quantitative assessment of the extent of the abnormalities within each tissue section. The absence of baseline normal histomorphology and numerical data however, makes it difficult to establish cause-and-affect relationships between pathology and contamination patterns in various fish species. It is imperative therefore, that the normal histomorphology of organs in fish species occurring in this region should be known so that histopathological conditions maybe accurately diagnosed…

M.Sc. (Zoology)
The Vaal River system is constantly subjected to pollution from various industrial, mining and agricultural activities. Consequently, pressure is continually exerted on the health of its fish communities and it was suspected that this may be a contributing factor to the repeated fish kills that have occurred in various sections of the river over the past few years. The aim of this study was to assess the health status of three fish species that were affected by the most recent mass fish mortality in the Vaal River. This was done using a combination of techniques including a histology-based health assessment (HHA) that involved a standard fish necropsy, the evaluation of blood parameters as well as a microscopic assessment of the liver, kidney, gills, and gonads. The histological results were semi-quantitatively assessed. Selected chemical substances were also tested for in water, sediment and the skeletal muscle tissue of the fish. Clarias gariepinus, Labeo capensis and Labeo umbratus specimens were collected from the Vaal River, approximately 2480m below the Vaal Dam (Latitude 26°51'17.47"S; Longitude 28° 7'16.58"E) following the latest occurrence of a fish kill in November 2011. Fish were collected using gill nets. Water was sampled in triplicate at three locations, and in situ measurements were done for selected physico-chemical parameters. Sediment samples were also collected and subjected to a sequential extraction technique and quantification of the heavy metals was done using Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Metals in skeletal muscle tissue and water were quantified using the same technique. An analysis of variance (ANOVA), followed by the appropriate post-hoc test was performed to determine differences between means of variables i.e. morphometric, histological, substance concentration and blood parameters...