Influence of Dietary Soya Beans (Glycine Max (L.) Merr.) Protein and Lipid Combination, and Androgen (17 α – Methyl Testosterone) Levels on the Growth and Reproduction of Oreochromis Andersonii (Castelnau, 1861)

In order to investigate the influence of dietary soya bean protein and lipid combination, and androgen (17 α – methyl testosterone (MT)) levels on the growth, reproduction and sex ratios of Oreochromis andersonii (Castelnau, 1861), four experiments were conducted. In the first and second experiments, the fish were reared in 40 hapas for 55 days set in a Randomised Complete Block Design (RCBD) factorial structure with three levels of lipid and protein; 10%, 15% and 20% lipid, and 20%, 30% and 40% protein respectively. In the third and fourth experiments, fish were subjected to isonitrogenous (30%) and isocaloric (4.02 kcal/g) diets incorporated with three levels of MT at 40 mg/kg, 60 mg/kg and 90 mg/kg of feed laid in a Complete Random Design (CRD). Growth performance of O. andersonii was significantly affected (P< 0.05) by different combinations of dietary protein and lipid with the best final weight and body weight gain (BWG) achieved at 20% crude lipid and 40% crude protein combination although not significantly different (P> 0.05) from any combinations with 30% and 40% crude protein. There were no significant differences (P> 0.05) in the fish growth indices among the lipid levels used although polynomial regression showed 15.3% to have given the highest body weight gain. Gross margin (GM) and total cost (TC) were highest too at the highest lipid and protein combinations. This also shows that protein level may be more important in fish feeds than lipid level. The study showed that fecundity and Gonadosomatic Index (GSI) were maximized at 15% crude lipid and 20% crude protein while the egg size was maximized at the 15% crude lipid and 40% crude protein combinations. However, the number of eggs incubated was maximized at the highest protein (40%) and lipid (20%) levels used in the experiment. The study showed that female O. andersonii can spawn without the presence of males and mature earlier than males. Fast growing fish were more likely to mature earlier than slow growing ones. The study revealed that the growth of O. andersonii was maximized when the feed was incorporated with the 60 mgMT/kg although the highest GM was observed in the control group (without MT). The GSI, Gonadal Index (GI) and egg size were not significantly different (P> 0.05) among the MT levels. This was also confirmed by the functional gonads as observed by the histological examination of the gonads. The anabolic effect achieved during oral administration of the androgen in the first 30 days of life declined with time. The study showed that the oral administration of MT does not affect the physiology of O. andersonii as the haematology chemistry and histopathology of the liver and heart were similar (P> 0.05) to that of the control. The 60 mgMT/kg feed achieved 94.4% males although this was not significantly different (P > 0.05) from the 93.4% males produced by the 40 mgMT/kg feed treatment. However, males were significantly skewed (P< 0.05) from the control group (54.3%) and the 90 mgMT/kg feed (79.3%). In conclusion, the studies suggest a combination of 30% crude protein and 10% crude lipid sourced from soya bean and maize in the culture of O. andersonii but optimised at higher than 40% for protein and at 15.3% for lipid for growth. Egg size is maximised at a combination of 40% crude lipid and 15 % crude lipid a combination recommended for brood stock. The studies further suggest a 60 mgMT/kg feed in the sex – reversal of O. andersonii.