Abstract:This experiment was conducted to investigate the effects of small molecule weight fish protein hydrolysate on the growth performance and the expression of insulin-like growth factor I receptor (IGF-IR) mRNA in the liver of juvenile turbot (Scophthalmus maximus L.). Four isonitrogenous and isoenergetic diets were formulated and fed to fish with initial weight of (4.16±0.01) g. In the experimental diets, fish meal was replaced with fish protein hydrolysate by 0% (UF-0), 5% (UF-5), 10% (UF-10), and 20% (UF-20) of total dietary protein, respectively. The experiment lasted 12 weeks. The results showed that there were no significant differences in the weight gain rate and specific growth rate among groups UF-0, UF-5 and UF-10 (P>0.05), but these groups showed higher values than group UF-20 (P<0.05). UF-0 and UF-5 showed similar feeding rate (P>0.05), which was significantly lower than that of UF-10 and UF-20 (P<0.05). The feed efficiency, protein efficiency, and protein retention effiency of UF-0 and UF-5 were significantly higher than those of UF-10 and UF-20 (P<0.05), and the parameter values of UF-10 were significantly higher than those of UF-20 (P<0.05). There were no differences in the contents of crude protein and crude lipid among groups UF-0, UF-5 and UF-10 (P>0.05), but the values in these groups were higher than those of UF-20 (P<0.05). The content of essential amino acids in the muscle and the ratio of essential amino acids to non-essential amino acids in group UF-5 was higher than those of other groups (P<0.05). It was also found that the expression of insulin-like growth factor I receptor (IGF-IR) mRNA in the liver increased with increasing levels of dietary fish protein hydrolysate, and it was higher in UF-20 compared to other three groups (P<0.05). These results indicated that low level of small molecule weight fish protein hydrolysate could improve the growth and feed utilization of juvenile turbot. However, higher level may restrain the growth. Furthermore, dietary fish protein hydrolysate could improve the expression of IGF-IR mRNA in the liver of juvenile turbot.
