Este estudo foi desenvolvido com finalidade de investigar o impacto da espécie exótica Clarias gariepinus no rio Itanhém, BA, tendo como referência o rio Caravelas. Foram analisados 214 estômagos de Clarias gariepinus, Centropomus undecimalis e C. parallelus desses dois locais. Brachyura compôs 92,8% da dieta de C. parallelus do rio Caravelas, enquanto que para C. undecimalis Teleostei compôs 72,5%. No rio Itanhém, os camarões foram mais importantes na alimentação de Clarias gariepinus, e para C. parallelus, Teleostei (98,1%). Não ocorreu sobreposição alimentar em nenhum dos casos estudados. Para caracterizar a ictiofauna, foram capturados 915 indivíduos do rio Caravelas e 2644 indivíduos do rio Itanhém. A espécie mais importante de Caravelas foi Diapterus auratus, e em Itanhém foi Stellifer naso. As variações da abundância da ictiofauna estiveram associadas, principalmente, à variação da salinidade. Para caracterizar as comunidades de pescadores e a problemática do Clarias gariepinus, aplicaram-se questionários socioeconômicos. Segundo os entrevistados (17 de Caravelas e 12 de Alcobaça), a espécie exótica traz como principais problemas, insuficiência de comercialização, predação sobre camarão e diminuição da renda dos pescadores. Pelos resultados desse trabalho não foi possível detectar indícios de mudanças na população de C. parallelus do rio Itanhém, apesar do impacto econômico detectado. / This work was developed in order to investigate the impact of the alien species Clarias gariepinus in the Itanhém River comparing to the adjacent Caravelas River, where this species does not occur. A total of 214 stomachs from C. gariepinus, Centropomus undecimalis, C. parallelus were analyzed. In Caravelas River, Brachyura was the main food item for C. parallelus, and Teleostei for C. undecimalis. In Itanhém River, shrimp was the most important food for C. gariepinus, and Teleostei for C. parallelus. There was no food overlap between the species within and among rivers. To characterize the fish fauna, 915 individuals and 2,644 were captured in Caravelas and Itanhém Rivers, respectively. Diapterus auratus was the most important species in Caravelas, while Stellifer naso in Itanhém. Seasonal variability on fish fauna was related to salinity. Twenty-nine questionnaires were applied to the local fishermen in order to evaluate the impact of the Clarias gariepinus introduction on the ecosystem and fishery. The main problems reported were that the C. gariepinus has no commercial value, they prey on shrimp, and the decreasing profit from fishery. There is no evidence of changes in the Centropomus parallelus population induced by the alien species, despite of its economic impact.

Este estudo foi desenvolvido com finalidade de investigar o impacto da espécie exótica Clarias gariepinus no rio Itanhém, BA, tendo como referência o rio Caravelas. Foram analisados 214 estômagos de Clarias gariepinus, Centropomus undecimalis e C. parallelus desses dois locais. Brachyura compôs 92,8% da dieta de C. parallelus do rio Caravelas, enquanto que para C. undecimalis Teleostei compôs 72,5%. No rio Itanhém, os camarões foram mais importantes na alimentação de Clarias gariepinus, e para C. parallelus, Teleostei (98,1%). Não ocorreu sobreposição alimentar em nenhum dos casos estudados. Para caracterizar a ictiofauna, foram capturados 915 indivíduos do rio Caravelas e 2644 indivíduos do rio Itanhém. A espécie mais importante de Caravelas foi Diapterus auratus, e em Itanhém foi Stellifer naso. As variações da abundância da ictiofauna estiveram associadas, principalmente, à variação da salinidade. Para caracterizar as comunidades de pescadores e a problemática do Clarias gariepinus, aplicaram-se questionários socioeconômicos. Segundo os entrevistados (17 de Caravelas e 12 de Alcobaça), a espécie exótica traz como principais problemas, insuficiência de comercialização, predação sobre camarão e diminuição da renda dos pescadores. Pelos resultados desse trabalho não foi possível detectar indícios de mudanças na população de C. parallelus do rio Itanhém, apesar do impacto econômico detectado. / This work was developed in order to investigate the impact of the alien species Clarias gariepinus in the Itanhém River comparing to the adjacent Caravelas River, where this species does not occur. A total of 214 stomachs from C. gariepinus, Centropomus undecimalis, C. parallelus were analyzed. In Caravelas River, Brachyura was the main food item for C. parallelus, and Teleostei for C. undecimalis. In Itanhém River, shrimp was the most important food for C. gariepinus, and Teleostei for C. parallelus. There was no food overlap between the species within and among rivers. To characterize the fish fauna, 915 individuals and 2,644 were captured in Caravelas and Itanhém Rivers, respectively. Diapterus auratus was the most important species in Caravelas, while Stellifer naso in Itanhém. Seasonal variability on fish fauna was related to salinity. Twenty-nine questionnaires were applied to the local fishermen in order to evaluate the impact of the Clarias gariepinus introduction on the ecosystem and fishery. The main problems reported were that the C. gariepinus has no commercial value, they prey on shrimp, and the decreasing profit from fishery. There is no evidence of changes in the Centropomus parallelus population induced by the alien species, despite of its economic impact.

M.Sc. / Sperm, eggs, free embryos and larvae of the sharptooth catfish, Clarias gariepinus, were used in a series of experiments conducted with zinc and copper salts in a flow-through exposure system. Metal concentrations ranged between 0 to 9mg/1 water. The aim of the study was to determine which of these early life stages was the most sensitive towards these metals and to determine whether the early life stages of the sharptooth catfish could be used for rapid bioassesment studies. Parameters investigated were sperm quality, egg hatchibility, free embryo and larval survival and growth. Within all the parameters tested sperm quality proved to be the least sensitive, with no significant changes noted at the metal concentrations used. There are notable reductions on hatching success embryonic and larval survival and growth as metal concentrations increased. Results revealed that the most sensitive was the free embryo stage directly after, and up to 48 hours after hatching. 48 hour old free embryo displayed 48th L.C.50 values as low as 1.98mg/l for zinc and 0. 0.13mg/l for copper, which indicated that this stage was very sensitive and susceptible to environmental stressors. Since C. gariepinus is an indigeniuos species that is widespread throughout the African continent and considering the sensitivity of the early life stages it is a succesfull candidade for use in rapid bioassessment tests throughout the continent.

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.

Photoperiod manipulation is routinely used in the aquaculture industry with the aim to enhance growth by manipulating the timing of reproduction in several commercially important temperate fish species. However, there are clear gaps in our understanding of how photoperiod is perceived by the circadian axis and transmitted to the brain to alter reproduction. Furthermore, due to the wide range of environments inhabited by fish, it is unlikely that one single organization exists. It is therefore believed that comparative studies of temperate species “models” with tropical species such as the African catfish (Clarias gariepinus) that adapted to different environments characterized by weaker light signals can help in such an aim. A number of studies were therefore performed in this PhD project to expand our knowledge on circadian biology and environmental physiological effects in African catfish. The first aim was to characterize the circadian melatonin system in this species (chapter 3). Results clearly showed that the control of melatonin production by the pineal gland was very different in the African catfish as compared to temperate species such as salmon and trout. Indeed, melatonin production appeared to mainly depend on light stimuli perceived by the eyes as opposed to salmonids where light directly perceived by the pineal gland regulates its own melatonin production within photoreceptors. The main evidence was obtained in ophthalmectomised fish that were unable to synthesize and release melatonin into the blood circulation during the dark period. This was the first time that such a decentralized organisation, similar in a way to the mammalian system, was found in any teleost species. In vitro results also supported such findings as African catfish pineal glands in isolation were not able to normally produce melatonin at night as usually seen in all other fish species studied so far. This indirectly suggested that pineal gland photo-sensitivity might be different in this tropical species. Further studies were performed to better determine the amount of light that can be perceived by the African catfish pineal gland depending on light transmittance though the skull (where the pineal gland is located). Surprisingly, it appeared that catfish cranium act as a stronger light filter than in other species resulting in lower light irradiance of the pineal gland. This could explain, although it still needs to be further confirmed, why African catfish photic control of melatonin produced by the pineal would have evolved differently than in temperate species. The work then focused on better characterizing diel melatonin production and endogenous entrainment through exposure to continuous photic regimes (continuous light, LL or darkness, DD) (chapter 4). Daily melatonin profiles of fish exposed to 12L:12D photoperiod (routinely used in indoor systems) confirmed low melatonin production at day (<10 pg/ml) and increase at night (50 pg/ml) as reported in most vertebrate species studied to date. Interestingly, results also showed that melatonin production or suppression can anticipate the change from night to day with basal melatonin levels observed 45 mins prior to the switch on of the light. These observations clearly suggest the involvement of a clock-controlled system of melatonin secretion that is capable of anticipating the next photophase period. Furthermore, when constant light (LL) was applied, day/night melatonin rhythms were abolished as expected due to the constant photic inhibition of AANAT activity (e.g. one of the enzyme responsible for the conversion of serotonin into melatonin). However when fish were exposed to constant darkness (DD), a strong endogenous melatonin rhythm (maintained for at least 4 days and 18 days in catfish and Nile tilapia respectively) was found, demonstrating once again the presence of robust circadian oscillators in this species. The next aim of the doctoral project was then to investigate circadian behaviour of catfish through locomotor activity studies (Chapter 5). African catfish is again a very interesting “model” due to its reported nocturnal activity rhythmicity as compared to most other teleosts species. Locomotor activity is considered as a very useful tool to elucidate the mechanisms of circadian organization in both invertebrates and vertebrates circadian. Results first confirmed the nocturnal activity rhythms in the species. Furthermore, clear circadian endogenous rhythms were observed under constant light (LL) or darkness (DD) during several days before losing rhythmicity. Interestingly, the activity levels varied depending on the stocking density. Finally, the last aim of this project was to test the effects of a range of photoperiodic manipulations on growth performances, sexual development and reproductive performances in African catfish reared from eggs to puberty. Results did not show any differences at the early sages (up to 90 days post hatching) in growth performances nor mortality (high) between control 12L:12D and LL treatments. In contrast, during the juvenile-adult period (from 120 to 360 DPH), significant growth effects were observed, as previously reported in other catfish species, with fish under LL displaying lower growth rate, food consumption and feed conversion efficiency in comparison to most other treatments (12:12, LL, 6:6, 6:18, 12-LL and LL-12) especially 12l:12D. However, no major effects of the photoperiodic treatments were observed with all fish recruited into puberty and developing gonads although differences in the timing of gametogenesis could be observed, especially a delay (circa 2 months) in females exposed to short daylength (6L:18D and 6L:6D). As for egg quality, egg diameter was the only parameter to differ between treatments (slightly larger in egg batch from LL treated females). Overall, none of the photoperiodic regime suppressed maturation in African catfish as opposed to some temperate species. The work carried out during this PhD project clearly advanced our understanding of circadian rhythmicity, light perception and effects of photoperiod on physiology in a tropical species. Future studies are now required to further characterise the circadian system and link it to evolutionary trends within vertebrates.

M.Sc. / There has been an increasing concern worldwide regarding the possible adverse effects of pharmaceutical supplements present in our aquatic ecosystems and whether or not they modify or alter physiological functioning in humans and wildlife. Trenbolone acetate (TBA) for example, is a commonly used androgenic anabolic steroid used in the production of cattle. TBA is metabolized into trenbolone-β and excreted as both trenbolone-α and -β. In liquid manure trenbolone-β has a half-life of over 270 days. Therefore if released into the surrounding environment there could be severe ecological impacts. The aim of this study was to determine the physiological effects of hormones used as growth stimulants in cattle production on the Sharptooth Catfish - Clarias gariepinus. The growth stimulants assessed in this study included; Trenbolone acetate, Methyltestosterone, Diethylstilbestrol and Zeranol. The aim was pursued with the use of three biomarker assays - Glutathione-S-transferase (GST), Uridine-Diphosphate Glucuronosyltransferase (UDPGT) and Cellular Energy Allocation (CEA). Fish were exposed under controlled conditions for a period of 5, ten and 15 days respectively using a flow-through system. Testes were removed and standard histological techniques were employed. Selected target organs were removed and immediately frozen in liquid nitrogen and stored at -80°C until needed for biomarker analysis.The results obtained from the gonado-somatic Index (GSI) showed that there were no significant differences (p<0.05). The hepato-somatic index (HSI) increased throughout all the different exposure groups. The histological assessment showed no significant alterations in the cell structure of the testes. With regards to the biomarkers used, CEA reflected changes in both the energy available and the energy consumed by the test organisms during the exposures. A common trend was observed throughout the different exposures. A change would occur after the ten day exposure period however a recovery would be made after 15 days of exposure. Both GST and UDPGT reflected increased activity in the liver with GST reflecting a significant difference (p<0.05) between the control and the exposure groups, however GST activity in the kidneys were not affected. To conclude, further studies will be needed to determine whether or not these growth stimulants will have a significant effect at higher concentrations and over longer exposure periods.

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. / A lot of research in ecotoxicology is currently focused on identifying and developing suitable biomarkers for use in assessing the health of aquatic systems. Thus this study was done as part of a major project aimed at identifying and selecting suitable biomarkers to use in the Rietvlei System, South Africa. This study focused on the response of Clarias gariepinus (Burchell, 1822) to contaminants using three biomarkers: population genetic structure, DNA damage and metallothioneins (MT¡¦s). The main objectives of the study were to assess the potential of these biomarkers in C. gariepinus and to provide baseline data on the Rietvlei System. Eighteen enzyme loci (creatine kinase (Ck), esterase (Est), phosphoglucomutase (Pgm), glycerol-3-phosphate dehydrogenase (G3pdh-1 and -2), glucose-6-phosphatase isomerase (Gpi-A and -B), L-lactate dehydrogenase (Ldh-A and B), malate dehydrogenase (sMdh-1, -2 and -3), malate dehydrogenase (NADP+) (Mdhp), phosphogluconate dehydrogenase (Pgdh), isocitrate dehydrogenase (NADP+) (Idh); superoxide dismutase (Sod), and peptidase: substrate (leucyl tryrosine) (Pep-S1 and -2)) were screened for by horizontal starch gel electrophoresis. An agarose gel electrophoretic method was used for DNA damage determination and a spectrophotometric method for metallothionein. The Rietvlei System population (RSP) showed higher genetic variability as shown by the average number of alleles per locus (A), proportion of polymorphic loci (P) and expected average heterozygosity (HE) than the reference populations. Statistically significant deviations (p < 0.05) from Hardy-Weinberg proportions associated with heterozygote deficiencies occurred at Gpi-B, Idh, Pgdh, Ldh-A and Pep-S1 for RSP. These deviations could have been a result of small sample size. There was high genetic differentiation between RSP and the reference populations with FST values of 0.450 and 0.480 between RSP and wild population (WP) and RSP and Northern Cape population (NCP) respectively. A mean base-pair length of 6770.9 „b 10.68 (SE) bp was recorded in the Marais Dam population (MDP) that of 6327.2 „b 17.69 (SE) bp was recorded in the Rietvlei Dam population (RDP). The MDP had a higher proportion of DNA fragments with low base-pair lengths than RP indicating a higher level of DNA damage. The level of DNA damage in the MP was higher than in the RDP. The mean MT¡¦s content was 3.63 „b 0.643 (SE) nmol g-1 wet weight in the MDP and 4.35 „b 0.580 (SE) nmol g-1 wet weight in the RDP. There was no significant (p = 0.40) difference in the levels of MT¡¦s between the two dams. It was concluded that there were significant differences in genetic diversity between RSP and the other populations in unpolluted sites; hence genetic diversity in C. gariepinus has potential as biomarker of pollution. However, further research is recommended to investigate possible contributing factors to differences in genetic diversity such as inter-sex males, geographical isolation and differences in sample sizes used. DNA damage is also a potential biomarker provided due care is taken in interpreting average base-pair length data to consider differences in each DNA size class. It seems further research is required before conclusions are made about use of MT¡¦s as biomarker in this population. The levels of MT¡¦s in other uncontaminated systems will be useful to determine whether the levels recorded in this study are background levels or responses to contamination. / Prof. F.H. van der Bank

The need for developing an artificial dry feed for Clarias gariepinus larvae was identified. Dry larval fishfeed requires certain physical properties. Techniques for manufacturing feeds which comply with these requirements were evolved and are recomended for practical use. The techniques that were used for artificial reproduction of C. gariepinus larvae are briefly discussed. The larvae were fed on various dietary formulations and their growth responses were monitored in order to determine their nutritional requirements. A feed was developed which gave superior results to those obtained with natural food organisms. This feed consisted of Torula yeast(69,8%), fishmeal(23,3%), vitamin supplements(O,9%), methionine supplement (150mg/kg), bactericide and preservatives. The feed particles were coated with a lipid supplement which was added at a ratio of 6% to the weight of the feed. The optimum particle size (diameter) for C. gariepinus larvae is 2,2% of their mean total length. The larvae should be given a feed ration of 25% of body weight per day at a frequency of once every four hours. A favourable feed conversion ratio of 1.1g of feed consumed per gram of larval weight gain was experienced. The established dry feed is suitable for use in commercial hatcheries and can be used as a standard and proven food source for further research on the intensive rearing of C. gariepinus larvae.

Ph.D. / Female adult specimens of Lamproglena clariae attach to gill filaments of freshwater fish of the family Clariidae, penetrate the gill tissue and consume blood. Previously, studies have been done on the taxonomy of this parasite, but little research has been published on biological aspects. Hence, it was the aim of this study to determine and record L. clariae’s aspects of biology such as ecology, life cycle and pathology. The study was conducted through both field and laboratory observations with specimens collected from the Vaal Dam and Vaal River Barrage. A positive correlation was observed between the host's physical dimensions and the size of the parasite, parasites from both sites preferred the fourth gill and the median part of the gill arch for attachment. There was no significant host gender preference by parasites. Three free living nauplius stages, four copepodite, a cyclopoid and adult stages were recorded as life stages of this parasite. Observations suggested that development of larval stages of L. clariae is influenced by both photoperiod and temperatures. Furthermore low infestation success of the experimental fish was observed. This parasite caused localised infestation as varying degrees of swelling of gill filaments were observed only in the vicinity of its attachment site. Histological examination revealed epithelial hyperplasia, resulting in fusion of gill lamellae and necrosis of the host tissue in the vicinity of the parasite. No correlation exists between the infestation intensity and fish haematocrit values. Although L. clariae causes localized infestation, high intensity of infestation may be detrimental to the fish. Hyperplasia of epithelial tissue resulting in fusion of lamellae would result in restriction of oxygen passage and thus hinder the process of respiration of the host. / Prof. A. Avenant-Oldewage