THE INFLUENCE OF DIETARY ENERGY-LEVELS WITH AND WITHOUT PCB INDUCTION ON THE GROWTH OF TILAPIA, OREOCHROMIS-NILOTICUS X OREOCHROMIS-AUREUS

The effects of three dietary energy levels, 323, 365 and 408 Kcal/100g diet, on the growth performance of hybrid tilapia, Oreochromis niloticus x O. aureus, were studied. The experiment was carried out for 3 months in a recirculating rearing system. Growth and feed conversion ratios were significantly reduced (p<0.05) in fish exposed to 100 ppm polychlorinated biphenyl (PCB), fed high energy diets (365 and 408 Kcal/100g diet). The hepatic cytochrome P-450 and NADPH-cytochrome c reductase activities were also significantly (p<0.05) lower in PCB-treated fish fed high energy diets (365 and 408 Kcal/100g diet) than fish fed lower energy diet (323 Kcal/100g diet). The malic enzyme activity and the body lipid content in fish generally increased as the dietary energy level increased.