Optimal dietary lipid level for growth of juvenile hybrid tilapia, Oreochromis niloticus x Oreochromis aureus

A growth experiment was conducted to determine the optimal dietary lipid level of juvenile hybrid tilapia, Oreochromis niloticus X Oreochromis aureus. Five isoenergetic and isonitrogenous purified diets containing 0-20% lipid (corn oil/cod liver oil/lard, 1:1:1) in 5% increments were fed for 8 weeks to triplicate groups of tilapia in a recirculated filtered rearing system maintained at 21 degrees C. Weight gain was higher in fish fed the 10 and 15% lipid diets, followed by the 5% lipid diet, then by the 20% lipid diet and was lowest in fish fed the lipid-free control diet, Protein efficiency ratio (PER) and protein deposition in fish generally followed the same pattern of weight gain. Feed conversion ratios (FCR) were better (P < 0.05) for fish fed the lipid diets than those fed the control diet. Body lipid content was highest (P < 0.05) in fish fed the 20% lipid diet, followed by those fed the 10 and 15% lipid diets, and lowest in fish fed the 5% lipid diet and the control diet, Liver malic enzyme, glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were higher in fish fed the lipid-free control diet and generally decreased as the lipid content in the diet increased, Second-order regression of weight gain on concentrations of dietary lipid indicates that the optimal dietary lipid for maximal growth of O. niloticus X O. aureus is about 12%. Five percent of dietary lipid appears to meet the minimal requirement for this species.