Interactions between dietary protein levels, growth performance, feed utilization, gene expression and metabolic products in juvenile grass carp (Ctenopharyngodon idella)

The present study aims to evaluate the possible interactions between dietary protein levels, growth performance, gene expression and volatile compounds in the plasma and liver of juvenile grass carp. Juvenile grass carp (4.27 ± 0.01 g) were fed with six extruded purified diets containing different protein levels (200, 250, 300, 350, 400, 450 g kg- 1 dry diet) for 8 weeks. The best growth performance appeared in the 400 g kg- 1 dietary protein group, which had highest percent weight gain, protein retention, condition factor and lowest lipid retention, feed conversion ratio and whole body crude lipid among all the treatments. In addition, we found that fish fed with higher protein content diet was apt to have lower lipid content in muscle and liver. It may relate to the expression patterns of neuropeptide Y in the hypothalamus and acetyl-coA carboxylase 1 in both liver and hypothalamus. An analysis of volatile compounds in the plasma and liver showed that the concentration of several types of fatty acid and amino acid changed between the 400 g kg- 1 dietary protein group and 200 g kg- 1 dietary protein group. This may also contribute to the final growth performance.