Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Based on a number of attributes, the African sharptooth catfish, Clarias gariepinus is an ideal aquaculture species. Much work has been undertaken on developing the technology for the commercial culture of the species inclusive of determining the nutritional requirements for cost effective feed formulation. However, digestible energy (DE) values for specific feed ingredients were unknown. As DE values are not interchangeable between species, this study set out to determine the DE values for conventional and unconventional feed-ingredients for the formulation of an optimal feed. The ultimate goal in feed formulation is to produce a diet that supports the maximum production at the least cost. The indirect method was found to be most suitable in obtaining DE values for the catfish. Feed samples were marked by adding 2% chromic oxide as an inert indicator. The fish were then force-fed and faecal samples were obtained from the hindgut by stripping the fish 10 hours after feeding as this was found to be when the hind-gut was at its fullest and the feed maximally digested. A linear based computer programme was used to formulate experimental diets using the established DE values as an additional variable. The formulated feed was tested and compared to a commercial catfish diet and a standard reference diet (H-440). All of the newly formulated feeds were found to be cheaper to manufacture (by between 5 and 10%). Statistically (ANOVA), all of the experimental diets resulted in higher specific growth rates (SGR) than the standard reference diet. The commercial diet also resulted in a lower SGR than those experimental diets with similar protein levels.

The big-oui hybrid catfish (female C. macrocephalus x male C. gariepinus) was successfully achieved using artificial hybridization. This hybrid combines the superior taste of the C. macrocephalus with the faster growth rate and higher resistance to environmental conditions of the C. gariepinus and is now the biggest fresh-water aquaculture product in Thailand. In this thesis the results of experiments involving hybridization and genetic manipulation were used to investigate the nature of the hybridization event. This information was used to develop broodstock for Clarias catfish breeding programme. Allozyme studies resolved 18 protein loci encoding different enzyme systems in C. batrachus, C. macrocephalus, C. gariepinus and the big-oui hybrid. GPI-2*, MDH-2* and LDH-l* show clearly variation between the hybrid and the parental species and were used for species diagnostic loci. Comparisons of fertilisation and survival of the big-oui hybrid, reciprocal cross hybrid, F2 hybrid, back cross hybrid and their parental species were carried out. The only cross involving the F 1 big-oui hybrid still gave viable embryos and fry was between female F 1 hybrid and male C. gariepinus. The F2 hybrid never developed to hatch. Karyotyping studies showed a modal chromosome number of 2n=54 in C. macrocephalus; 2n=56 in C. gariepinus; 2n=55 in the big-oui hybrid, the reciprocal hybrid and the back cross hybrid. Using male C. gariepinus from two other stocks ('Malawee' and 'Wageningen') were carried out to produce the big-oui hybrid. Cold shock at 2°C administered for 15 mins duration and 4 mins after fertilisation was the most effective in inducing 100% triploidy in big-oui hybrid while heat and pressure shock were less effective. Growth performance of diploid and triploid hybrids was not significantly different. The triploid hybrid were shown to be functionally and endocrinologically sterile. Gynogenetic diploids were produced by fertilizing C. macrocephalus eggs with C. gariepinus sperm that had been genetically inactivated with ultraviolet (UV) light, and then cold shocking the eggs after fertilisation. The UV dose of 200 Il W cm -2 for 2 mins using a sperm concentration of 2.5 x 108 mrl was optimal in genetically inactivating sperm without seriously compromising motility. Cold shock at 2°C, started at 4 mins after fertilisation and 15 mins duration gave the maximum number of meiotic gynogenetic offspring. The parental contribution in the gynogenetic offspring was check by using the species diagnostic allozyme loci and showed no evidence of male contribution. Gynogenetic offspring were grown on to investigate the sex ratio. All gynogenetic offspring were female suggesting female homogamety in this species. The possible implications of the above results of hybridization and genetic manipulation studies in Clarias catfish culture are discussed.

Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 51-54).

Past and current research on the biology and culture of the sharptooth catfish (Clarias gariepinus) has stimulated the development of its commercial production. At the inception of this project in 1985, it was decided that the development of an optimal dry feed was the most important step in developing a more complete culture technology for the species. The objectives of the project were, therefore, to investigate aspects of the nutritional physiology and dietary requirements of the species to provide the necessary information for the formulation of optimum economical feeds. A review of the natural feeding biology of the species provided valuable information with regard to its food preferences. From this information, and by estimating the nutritional composition of its preferred natural diet, it could be concluded that the animal requires a relatively high dietary protein content. This conclusion was substantiated by studies of the functional morphology of the digestive system (gross and fine structure). The characteristics of the digestive system and external anatomy were found to be typical of an opportunistic, omnivorous predator. The ontogenetic development of the digestive system is relatively fast, and enables the utilization of a variety of diets efficiently from an early stage. Since the ability of an animal to digest a given substance is predominantly dependent on the presence of appropriate enzymes the quantification and characterization of C. gariepinus digestive enzyme activities were investigated on an experimental basis. This work revealed that the animal has relatively high levels of digestive enzyme activities, and that its proteolytic enzyme activities correspond with those of other carnivorous fishes, while its starch digesting abilities correspond with those of specialized herbivores. Also, the high levels of lysozyme and alkaline phosphatase indicate an adaptation to detritivory, making this fish a truly opportunistic omnivore. Evidence was found to suggest that sharptooth catfish are able to re-absorb secreted digestive enzymes in the posterior section of its intestinal tract. It was shown that digestive enzyme activities were induced by food intake, and that no inherent rhythmicity in digestive activities seemed to occur. The development of digestive enzyme systems in the early life history of this animal was found to be also extremely rapid (complete within 10-16 days after hatching). It was also shown that artificial dry feed stimulates higher levels of digestive enzyme activities in larvae and juveniles than natural food. Although increased cellulase activity was found in larvae and juveniles that were fed on live zooplankton, the relative contribution of exogenous prey enzymes to protein digestion could not be ascertained. Specific nutritional requirements were investigated by means of feeding trials. The results of these trials confirmed the above indications regarding the dietary requirements of sharptooth catfish. It was concluded that for optimal growth and production performance, this animal requires a dietary protein content of 40-42%, a dietary lipid content of 10-12% and that diets should contain 14-16 kJ/g digestible energy. The optimum protein-to-energy ratio was found to be 26-29mg protein per kJ of digestible energy. Dietary requirements are evidently the same for juveniles and adults, except that younger fish require higher relative feeding levels. Finally, practical feed formulations were evaluated in terms of their economic feasibility. The results of these trials are presented along with recommendations on the formulation of commercial feeds for C. gariepinus. A computer program with which to implement least cost feed formulation by means of linear programming is provided.

M.Sc. (Zoology) / Schilbeids or butter barbel represent a valuable source of protein for the people of Africa. Recently, several local producers commenced with the commercial production of butter barbel. To manage this resource and to provide a long-term sustainable yield, it is essential to have a thorough knowledge of the taxonomy, distribution, ecology and genetic structure of this species. By preserving the genetic structure of a species, erosion of its genetic variability is prevented, enabling them to adapt and consequently survive altering environmental conditions. However, several natural and anthropogenic influences acting upon the populations may affect their genetic variability and ultimately their survival ...

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