Effects of natural feeding stimulants and glutamic acid supplementation on the feed intake, growth performance and digestive enzyme activities of red sea bream (Pagrus major) fed fish meal-free soy protein concentrate (SPC)-based diet

Two experiments were conducted for red sea bream (Pagrus major). In experiment 1, the optimum level of glutamic acid and natural feeding stimulants to enhance feed intake were determined and found that glutamic acid level of 0.5% and fish meat hydrolysate (FMH) were effective. In experiment 2, fish were fed with soy protein concentrate (SPC)-based diet with synthetic feeding stimulants (Basal diet), the Basal diet with FMH (FMH diet), the FMH diet with glutamic acid (FMHG diet) and with fish meal diet (FM diet) as a control until satiation for 8 weeks. Feed intake of FMHG-fed fish was significantly higher than others (p < 0.05). Specific growth rate and the feed conversion ratio of FMHG were comparable to those of FM-fed fish (p > 0.05). Relative visceral fat ratio and crude lipid content of any SPC-based diet-fed fish tended to be lower than those of FM diet-fed fish. There were no significant differences in trypsin and lipase activities hepatopancreas among treatments. SPC can be utilized as a sole protein source in a diet for red sea bream. The lower growth performance in SPC-based diet-fed fish was not due to poor digestive enzyme secretion but could be associated with lipid utilization disorder.