Effects of dietary starch levels on growth, feed utilization, glucose and lipid metabolism in non-transgenic and transgenic juvenile common carp (Cyprinus carpio L.)

This experiment investigated the effects of dietary starch on growth performance, feed utilization, glucose and lipid metabolism of non-transgenic and growth hormone (GH) transgenic juvenile common carp (Cyprinus carpio L.). Transgenic common carp (TG fish) and non-transgenic (NT fish) were fed diets with five starch levels (0, 10%, 20%, 30%, 40%). After 41 days, TG fish showed higher growth and feed utilization at low-starch diets, while similar growth, lower feeding rate (FR) and slightly higher feed efficiency (FE) was observed at high-starch diets. Lower plasma glucose level and hepatic glycogen content were observed in TG fish, which could be related to the higher glycolysis (high gene expression of hexokinase (hk), p < 0.01) and gluconeogenesis (high gene expression of fructose-1,6-bisphosphatase (fbpase), p < 0.01; glucose-6-phosphatase (g6pase), p < 0.01) of TG fish. Compared to NT fish, weakened fat synthesis (lower gene expression of fatty-acid synthase (fas), p <0.01; acetyl-CoA carboxylase 1 (acc1), p < 0.01; acyl-CoA desaturase 1 (scd1), p = 0.011) and enhanced fatty acid oxidation (high gene expression of hormone-sensitive lipase (hsl), p =0.01; carnitine palmitoyl transferase 1a (cpt-1a), p < 0.01), led to the decrease of body lipid content in TG fish. On the other hand, with increased dietary starch, increased body lipid and hepatic glycogen contents were observed in both TG and NT fish, suggesting that high dietary starch levels promoted glycolysis, fat synthesis and inhibited gluconeogenesis, fatty acid beta-oxidation. Overall, TG fish showed higher growth performance at low starch diets, and higher ability of glycolysis, fatty acid oxidation and lower lipid synthesis than the NT fish.