INTERACTIONS OF VARYING DIETARY-PROTEIN AND LIPID-LEVELS IN YOUNG RED TILAPIA - EVIDENCE OF PROTEIN SPARING

A 12-week feeding trial was carried out with young red tilapia, a hybrid of Oreochromis mossambicus and O. niloticus, with a mean weight of 1.185 g. Three series of isocaloric, experimental diets of 15%, 20% and 30% protein content (by dry weight) and for each series, four diets of 6%, 12%, 18% and 24% lipid content were tested. At all three protein levels the best growth was obtained with diets of 18% lipid. Daily consumption (in mg/g fish day-1) was correlated negatively to the digestible energy content of the diets, and overall rate of growth positively to the mean daily protein consumption (per g fish per day). The food conversion ratio ranged from 1.10 (P3OL24) to 2.32 (P15L12), the protein efficiency ratio from 2.18 (P30L6) to 3.56 (P20L18) and apparent net protein utilization from 19.9% (P15L6) to 42.95% (P30L18), where P and L refer to dietary protein and lipid, and the subscripts to the approximate percentage. The carcass lipid and protein reflected the dietary regimes. The study indicates the protein-sparing capabilities of young red tilapia. The protein-sparing capability increased with increasing dietary lipid content up to 18% and decreased thereafter.