Growth and metabolic responses in Nile tilapia (Oreochromis niloticus) subjected to varied starch and protein levels of diets

In the present study, six diets were formulated to contain 24% or 36% protein, and 0, 20%, or 40% starch. The Nile tilapias (Oreochromis niloticus) were fed with the designed diets for 56 days. An overall increasing tendency of percent weight gain, feed efficiency, protein efficiency rate (PER), hepatosomatic index (HSI), and condition factor (CF), whole-body protein and lipid contents, plasma concentrations of triglyceride (TG), total cholesterol (T-CHO) and glucose, liver glycogen contents, liver activities of glucokinase, pyruvate kinase, fatty acid synthetase, lipoprotein lipase (LPL), glucose-6-phosphate dehydrogenase, and malic enzyme with increasing dietary starch level was noted. While the opposite trend was found for feed intake (FI), whole-body moisture and ash contents, liver activities of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Furthermore, all the parameters above were higher in fish fed the 36% vs. 24% protein diets, expect FI, PER, whole-body moisture, liver G6Pase and PEPCK were opposite, and furthermore HSI, whole-body lipid, liver glycogen and LPL were unaffected by dietary protein treatments. The results indicate that Nile tilapia appears to have a more sensitive response to dietary starch level than dietary protein level. Appropriate dietary starch supplementation could help promote the growth of the fish species. Low-dietary protein (24%) allowance may acquire growth comparable to that of Nile tilapia fed 36% protein diets when feed protein is provided only by fish meal with at least 20% starch supplementation