M.Sc. / Please refer to full text to view abstract

D.Sc. / Please refer to full text to view abstract

A description is given of the location, anatomy and morphology of the endocrine glands likely to be involved in controlling the reproductive cycle of C. gariepinus. Methods of identifying the secretory tissues in the light and electron microscopes are outlined. A review of the published results on homologous tissues from other teleosts is included and directions for further research on the endocrinology of C. gariepinus are discussed.

Mémoire (M.Res.Renouv.)--Université du Québec à Chicoutimi, 1995. / Document électronique également accessible en format PDF. CaQCU

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.

M.Sc. / Please refer to full text to view abstract

In order to investigate the interactions of dietary protein and energy and their utilisation by African catfish, Clarias gariepinus (Burchell, 1822) (12.43 ± 0.05 g), a series of four nutritional experiments (triplicate groups of 20 fish per 30-L tank at 28 ± 1°C, for 8 weeks) were carried out using fish meal based diets. Optimum dietary protein to energy ratio (P/E ratio) and optimum lipid to carbohydrate ratio (L/CHO ratio) were investigated. Based on optimised dietary P/E ratio and L/CHO ratio, optimum feeding regime and compensatory growth were also investigated in this species. In the experiments to optimise P/E ratio and L/CHO ratio fish were offered each diet at 5% of their body weight per day adjusted fortnightly. In the optimum feeding regime experiments, fish were offered each diet to appetite or to a restricted level. The restricted regimes were achieved by offering fish decreasing fixed feeding rates with increasing dietary protein level. Studies on compensatory growth were conducted in two phases each of 4 weeks. In the first phase, triplicate groups of 30 fish and in the second phase triplicate groups of 20 fish (per 30-L tank) were offered the diet in six mixed feeding schedules at two feeding regimes i.e. appetite and restricted. The restricted regime was achieved by offering fish 1% (maintenance ration) of their body weight per day adjusted after fortnightly weighing. Optimum dietary P/E and L/CHO ratios were 20.54-mg protein/kJ of GE and 0.40 g/g respectively, with a crude protein level over 40% and gross energy of more than 20 kJ/g GE. The results of investigating feeding regimes suggest that dietary protein level could be reduced from over 40% to 35% by feeding to appetite based on the above optimised dietary P/E and L/CHO ratios. Addition of dietary energy as lipid at varying protein levels resulted in increased growth, protein and energy utilisation in C. gariepinus. Based on optimised dietary P/E ratio, dietary carbohydrate levels were increased (with concomitant reduction in dietary lipid levels) resulting in a trend towards higher growth performance, protein and energy utilisation. Protein and energy utilisation did not vary (P > 0.05) with feeding regime or dietary protein level. C. gariepinus showed partial compensatory growth under alternating periods of feeding a restricted (maintenance requirements) and appetite ration and also showed higher feed, protein, lipid and energy utilisation efficiencies in comparison to appetite feeding.Increase in dietary lipid produced an increment in carcass lipid deposition, both in whole body and liver in all studies. Fish in all treatments did not show significant differences (P < 0.05) in body protein content. Optimum P/E ratio studies, with varying dietary protein and energy level, produced higher liver glycogen, plasma glucose and plasma triglycerides at higher dietary carbohydrate level with lower protein diets. In the studies to optimise lipid to CHO ratio comparatively lower (P < 0.05) plasma glucose and plasma cholesterol deposition were observed while no consistent trends were found in liver glycogen deposition in fish fed higher dietary lipid with concomitant lower CHO levels. Studies on optimising feeding regime, with varying protein levels, did not show any significant differences (P < 0.05) in liver glycogen, plasma glucose, plasma triglycerides and plasma cholesterol in response to dietary treatment. In all studies fish fed the experimental diets showed insignificant differences (P > 0.05) in plasma amino acid levels and digestive enzyme activities (protease and lipase) while intestinal a-amylase activity increased with increasing dietary carbohydrate level. Histological examination of intestine & liver in all studies showed no abnormalities. In conclusion, these studies suggest that manipulation and optimisation of dietary protein and energy intakes plays a very significant role in African catfish, Clarias gariepinus nutrition.

This work delves into the recently developed ‘Whedo’-aquaculture-system in the rural community of Malanville (North Benin)and aims on providing a closer insight on this – for the area--recent system including the ecological but also the sociological and economical aspects in order to develop this extensive traditional fishery to a more productive semi-intensive aquaculture system. With the retreat of the flood ‘Whedos’ usually become infested with numerous hydato-and tenagophytes, while the presence and density of the free-floating macrophytes were positively related to the nutrient content of the ‘Whedo’. Extensive plant infestation also affects water quality through the decomposition of organic material and its accumulation in thick mud layers on the pond bottom as well as through the nocturnal oxygen consumption. Unfavourable water quality, especially low dissolved oxygen as well as high conductivity and nitrite levels, was identified to be the main factor determining which fish species were able to survive the harsh conditions prevailing in the ‘Whedos’ during the dry season. With the deteriorating water quality with advancing dry season, fish diversity decreased significantly leaving only species that are highly adapted to such unfavourable conditions. The most abundant species were Clarias gariepinus, Heterotis niloticus, Oreochromis niloticus L., Hemichromis c.f. letourneauxi, Polypterus senegalus and Epiplatys spilargyreius. Besides, the investigations also concentrated on the fish diversity of the rivers Niger and Sota with the results that for three species distribution gaps could be closed and for further three species their already known distribution could be expanded. But otherwise it could also be detected that some economically important species that were abundant in the past. In regard to the ‘Whedo’-management, the investigations showed that the owners lack most of the knowledge on appropriate management strategies, e.g. the feeding and stocking regime. The exploitation period depends on the extent of the previous annual flood and the location of the ‘Whedo’ within the floodplain, but the main season is from February to April. The biomass harvested on a hectare basis separated for each of the ‘Whedos’ averaged 17 tons/ha in 2008 and 8.6 tons/ha in 2009. However, 72 percent of the total biomass of Clarias only had an average weight of 40 grams. Therefore, two separated feeding trials were conducted and in total 6 supplementary feeds were tested on Clarias gariepinus. Groundnut cake, fish trash, rice bran, blood meal and azolla meal were used in different combination and rations to formulate the experimental diets. Diet containing 19 percent blood meal resulted in the best economical benefits showing that the use of high quality feed ingredients such as groundnut cake is not recommendable because local fish prices are too low to compensate the additional feeding costs. Instead of high quality feed farmers should focus on ingredients that are free of charge and easy to process. The supplementation based on 19 percent blood meal resulted in the doubling of the net profit compared to the income based on feeding only rice bran, thus provided higher additional income, enhancing the livelihood of the fish farmers. Concluding, the ‘Whedo’-aquaculture system is still in its infancy but nevertheless is an attractive system for the rural population because of existing knowledge of post-flood wetland fisheries as well as the low investment needed for its installation. Additionally, the local fish supply will increase and hence not only contribute to a better provision of protein-rich food and reduced pressure on the wild fish stocks but might also prevent fish prices to increase in a way that the poor won’t be able anymore to afford their most important source of animal protein. But fish farmers need more knowledge on appropriate management strategies and thus should be provided with technical support to guarantee a successful development and not to discourage the owners as a consequence of avoidable failures. Furthermore, the use of supplementary feed offers a cheap and effective means to increase the biomass production and thus enhance the extensive fishery to a semi-intensive aquaculture system. / Die vorliegende Arbeit befasst sich mit dem unlängst entwickeltem ‚Whedo’-System im ländlichen Bezirk Malanville (Nordbenin)und wurde darauf ausgerichtet, nähere Erkenntnisse über die Bewirtschaftungsweise der ‚Whedos’ und deren jüngsten Entwicklungen in diesem Gebiet zu erlangen. Ein Einblick in die ökologischen, aber auch soziologischen and ökonomischen Aspekte ist die Grundlage für die Fortentwicklung dieser extensiven traditionellen Fischerei in eine ertragsreichere semi-intensive Fischzucht. Im Rahmen dieser Recherche wurden die Eigenschaften der ‚Whedos’ im Bezug auf die Art und Dauer der Überschwemmung untersucht. Mit dem Rückgang der Flut werden die Fischlöcher gewöhnlich von zahlreichen Hydato- und Tenagophyten überwuchert, wobei der Grad des Schwimmpflanzenbewuchses positiv mit dem Nährstoffgehalt des Wassers korrelierte. Die meisten Fischlöcher zeigten eine, mit fortschreitender Regenzeit abnehmende Wasserqualität. Schlechte Wasserqualität, vor allem geringe Sauerstoffkonzentrationen und hohe Salz- und Nitritgehalte, wurde als der bestimmende Faktor für das Vorkommen der Fischarten in den ‚Whedos’ während der Trockenzeit identifiziert. Die Fischdiversität nimmt mit zunehmender Verschlechterung der Wasserqualität signifikant ab und dienen nur noch Arten als Habitat, die an schlechte Wasserqualität speziell angepasst sind. Die häufigsten Arten waren Clarias gariepinus, Heterotis niloticus, Oreochromis niloticus L., Hemichromis c.f. letourneauxi, Polypterus senegalus und Epiplatys spilargyreius. Zusätzlich beschäftigte sich diese Arbeit auch mit der Fischdiversität der Flüsse Niger und Sota. In diesem Rahmen wurden für drei Fischarten Verbreitunglücken geschlossen und für drei weitere Arten deren bereits bekanntes Verbreitungsgebiet erweitert. Im Gegensatz dazu konnte jedoch auch festgestellt werden, dass ehemals stark vertretende Fischarten aus den Fängen der Fischer verschwunden sind. Der Zeitpunkt der Befischung hängt im Allgemeinen von der Flutintensität, der Lage des Fischloches innerhalb des Überflutungsgebietes und auch von den Marktpreisen ab, wobei die meisten Ernten zwischen Februar und April, kurz vor Beginn der nächsten Regenzeit im Mai, stattfanden. Der durchschnittliche Biomasseertrag, basierend auf den Werten der einzelnen ‚Whedos’ betrug 17 Tonnen im Jahre 2008 und 8,6 Tonnen im Jahre 2009. Um die Wachstumsraten der Fische zu verbessern wurden zwei unterschiedliche Fütterungsversuche durchgeführt. Erdnusspresskuchen, Fischabfälle, Reisspelzen, Blutmehl und Azolla-Mehl wurden in verschiedenen Zusammensetzungen und Anteilen als Grundlage der Futtermittel verwendet. Die Futtermittel mit einem Anteil von 10 bzw. 19 Prozent Blutmehl wurden von den Fischen während der gesamten Fütterungsperiode aktiv konsumiert und erzielten die höchsten Nettogewinne. Die Versuchsergebnisse zeigen deutlich, dass qualitativ hochwertige Materialien nicht als Ergänzungsfutter geeignet sind, da die geringen Marktpreise für Fisch die zusätzlichen Kosten nicht decken können. Anstatt qualitativ hochwertigem Ergänzungsfutter sollten die Besitzer Materialien bevorzugen, die kostenlos bzw. günstig und zudem einfach zu verarbeiten sind. Das Ergänzungsfutter mit einem Blutmehlgehalt von 19 Prozent erzielte, im Vergleich zur gewöhnlichen Fütterung mit Reisspelzen, einen zweimal höheren Nettogewinn. Das zusätzlich erwirtschaftete Nebeneinkommen könnte somit zu einem verbesserten Lebensunterhalt der Besitzer beitragen. Obwohl sich das ‚Whedo’-System noch in seinen Anfängen befindet, wird es von der ländlichen Bevölkerung aufgrund ihrer Erfahrungen bezüglich der Fischerei in den Überflutungsgebieten und der geringen Installationskosten, hoch geschätzt und weiter ausgebaut.

Assignment (MPhil)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--Rhodes University, 2004. / Title from PDF t.p. (viewed on Apr. 23, 2006). Includes bibliographical references (leaves 222-257).