Effects of dietary carbohydrate and lipid levels on growth and hepatic lipid deposition of juvenile tilapia, Oreochromis niloticus.

As the major non-protein energy sources, high carbohydrate (CHO) and lipid (L) diets have been widely used in aquaculture to reduce cost, but they also caused excessive lipid accumulation in the fish liver. It is not yet clear which, lipid or carbohydrate, is a greater influence on hepatic lipid accumulation. To study the effects of dietary carbohydrate and lipid levels on hepatic lipid deposition in Nile tilapia ( Oreochromis niloticus ), six diets with different carbohydrate and lipid levels (carbohydrate level ranged from 11.2% to 54.24%, while lipid level ranged from 21.51% to 2.70%, namely, the dietary CHO:L ratios ranged from 0.52:1 to 20.09:1) were formulated and fed to tilapia for 8 weeks. After the feeding trial, high specific growth rate (SGR) was observed in the groups with the CHO:L ratio of 1.95, 3.41 and 6.40. Hepatosomatic and viscerosomatic index increased as dietary CHO:L ratios increased. Low serum TG, CHL and HDL levels was observed in the groups with the CHO:L ratio of 6.40 and 20.09. Hepatic histology showed that the fish fed with dietary CHO:L ratios of 3.41 and 6.40 have more hepatic lipid droplets than fish fed with other diets. Hepatic gene expression data indicated that the cd36 transcript levels were significantly affected by dietary CHO:L ratios, with the highest expression in fish fed D4 and D5 with CHO:L ratio of 3.41 and 6.40. Higher transcript levels of lipogenic genes ( fas , acc-α and dgat2 ) were observed in the liver of fish fed with high CHO:L ratio diets, whereas FA β-oxidation genes ( cpt1 and acox1 ) expression were depressed in liver. Hepatic apoB100 expression was also down-regulated with the high dietary CHO:L ratios. These results suggested that dietary carbohydrates have a stronger effect on hepatic lipid accumulation than dietary lipids in tilapia. High dietary CHO:L ratios (> 3.41) accelerated the hepatic lipid deposition by increasing de novo lipogenesis and reducing FA β-oxidation and lipoprotein clearance in the liver, and diet with around 1.95 CHO:L ratio is suitable for tilapia culture concerning the growth performance and health. The present results will be of great significance in improving the utilization of dietary lipid and carbohydrate to achieve better nutrition efficiency in tilapia. [ABSTRACT FROM AUTHOR]