Enzyme-treated soybean protein concentrate is a highly effective plant protein for larval largemouth bass (Micropterus salmoides)

The enzyme-treated protein ingredients have been well documented to benefit the growth and development of fish larvae. To reduce fishmeal dependence in carnivorous fish larvae, enzyme-treated soybean protein concentrate (ESPC) was used to gradually replace enzyme-treated white fishmeal (EWFM) at inclusion levels of 0 (ESCP0), 5% (ESPC5), 10% (ESPC10), 15% (ESPC15) and 20% (ESPC20). The experimental diets were fed to triplicate groups of largemouth bass (initial weight 13.70 ± 0.01 mg) four times daily for 4 weeks. The results showed that replacing EWFM with ESPC had no significant difference in survival rate (P > 0.05), but linearly increased the growth performance (P < 0.05). The activities of trypsin, amylase and lipase in the intestine and liver were found to be significantly elevated in varying degrees with dietary ESPC addition (P < 0.05). Meanwhile, dietary ESPC inclusion possibly activated the target of rapamycin (TOR) pathway and inhibited the amino acid response (AAR) pathway in muscle, as evidenced by elevated expression of pept2, tor and s6, and decreased expression of eif2α, atf4 and redd1, respectively (P < 0.05). In addition, the expression of autophagy lysosomal pathway related genes (atg5, uvrag, sqstm, mul1a, bnip3la and bnip3b) was suppressed in varying degrees with dietary ESPC addition (P < 0.05). In summary, appropriate replacement of EWFM with ESPC could improve the growth performance of largemouth bass larvae through increasing digestive enzyme activities, activating protein anabolism and inhibiting protein catabolism, and dietary ESPC use could reduce EWFM content from 60 to 45%.