Expression of insulin-like growth factor genes in olive flounder, Paralichthys olivaceus, fed a diet with partial replacement of dietary fish meal

This study analyzed the expression of growth-related genes of olive flounder, Paralichthys olivaceus, fed a low-fish meal (FM) diet to investigate the replacement of the FM diet in the field. The expression of growth hormone (GH)/insulin-like growth factor (IGF) axis genes in the brain/pituitary/liver and plasma hormone concentrations were measured. A basal experimental diet was formulated using 63% FM and 12% soybean meal as the primary protein sources, and then two other diets were made by replacing 20% and 30% of the FM with soy protein concentrate, tankage meal, and poultry by-products meal. Each diet was fed to duplicate groups of juvenile flounder (150 +/- 3.0 g) twice a day. After 20 weeks, the plasma growth-related hormone concentrations were similar between the control and FM20 groups. Moreover, GH/IGF axis gene mRNA expression in the brain/pituitary/liver was similar between the control and FM20 groups. Immunoblotting of muscle and liver showed the same pattern. This study showed the utility of replacing 20% of the FM diet and supports the possibility of field application.