Effects of salinity and food consumption on growth and protein turnover in Nile tilapia (Oreochromis niloticus Linnaeus)
This thesis examines the effects of salinity, ration level, stocking density and level of protein in diet on food consumption and growth in individual Nile tilapia (Oreochromis niloticus Linnaeus), held in groups and reared under various culture conditions. Nile tilapia reared in different salinities (0, 10 & 20) but fed the same ration level (2% body weight day-1), showed no significant differences in growth or white muscle protein concentrations. During feed deprivation, weight loss was similar for fish held on 0 and 10 , but after 7 days over 50% of the fish maintained at 20 developed body lesions covering 5-25% of the body. The social hierarchy structure was similar for all groups of individual fish in all salinities; 25% of the fish were dominant (18.29% above an equal share of meal), 30% were subordinate (16.19% below an equal share of meal) and 45% fish were within an equal share of meal. Fish were observed to exhibit aggressive behaviour when feeding and it is assumed that the 2% body weight day-1 ration level was restrictive for the fish. The effects of ration levels on relationships between growth and food consumption of Nile tilapia were examined under different salinities. Salinity did not have a significant effect on the growth of fish fed at different rations. Growth of male fish was significantly (ANOVA, P < 0.05) better than female fish for all three salinities (0, 10 & 20 ) and two ration levels (3 and 4.5% body weight day-1).