The effects of valine level on plasma biochemical indexes, lipid content and gene expression involved in lipid metabolism in cobia (Rachycentron canadum)

The present study was conducted to investigate the effects of dietary valine on plasma biochemical indexes, lipid content and gene expression involved in lipid metabolism in cobia (Rachycentron canadum). Fish mean initial weight, (40.90.8) g were fed with soybean meal based on diets with graded levels of valine (1.26%, 2.21% and 2.62%) for 10 weeks. Results showed that lipid content of the whole body and muscle of fish fed the diet with deficient valine (1.26%) was significantly lower than that fish fed the moderate (2.21%) and excess (3.23%) valine treatment groups (P0.05). Plasma total protein (TP) fish increased significantly as dietary valine increased from 1.26% to 2.21% (P0.05), and kept relatively constant when dietary valine level was above 2.21% (P0.05). Plasma total cholesterol (TC) and the lipid content of liver increased with dietary valine increasing from 1.26 % to 2.21% (P0.05), but decreased with higher levels of dietary valine (2.21% to 2.62%) (P0.05). Hepatic mRNA levels of lipid synthesis related genes (SREBP-1, and FAS) were significantly up-regulated in fish fed the diet with moderate level of valine (2.21%) (P0.05), while hepatic mRNA transcriptional levels PPAR were significantly elevated in fish fed the diet with high level of valine (P0.05). Overall, results of this study suggested that valine deficiency could decrease lipid content and inhibit expressions of some lipid synthesis related genes of cobia. This may contribute to understanding the mechanisms related to the physiological effects of dietary valine in cobia.