Effects of fishmeal substitution by α-galactosidase hydrolytic soybean meal (EhSBM) on growth, antioxidant capacity, inflammatory responses and intestinal health of turbot juveniles (Scophthalmus maximus L.)

An 8-week feeding trial was conducted to study the effects of fishmeal substitution by different levels of alpha-galactosidase hydrolytic soybean meal (EhSBM) on growth, antioxidant capacity, inflammatory responses and intestinal health of turbot juveniles (Scophthalmus maximus L.). Four isonitrogenous (47.63% crude protein) and isolipidic (10.87% crude lipid) diets were formulated. The FM diet (the control diet) was formulated with 55% fishmeal. On basis of the FM diet, three experimental diets (Diets EhSBM40, EhSBM45 and EhSBM50) were formulated with 40%, 45% and 50% fishmeal protein substitution by EhSBM protein, respectively. Each diet was randomly allocated to triplicate groups in fiberglass tanks (200L), and each tank was stocked with 30 fish (initial weight 4.87 +/- 0.01 g). Results showed that there were no significant differences in survival rate, feed intake and feed efficiency among dietary treatments (P > 0.05). The specific growth rate (SGR) of turbot juveniles showed a significantly linear decrease with increasing dietary EhSBM (P < 0.05), while no significant difference was found in fish fed diets control and EhSBM40 (P > 0.05). With increasing dietary EhSBM, the apparent digestibility coefficient of dry matter (ADCD) and protein (ADCP) exhibited significantly quadratic and linear decline, respectively (P < 0.05). When replacing EhSBM protein >40%, the ADCD and ADCP were significantly lower than those of the control group (P < 0.05). The foregut trypsin and alpha-amylase activity exhibited significantly linear decrease with increasing dietary EhSBM (P < 0.05). Fish fed diets EhSBM45 and EhSBM50 exhibited significantly lower trypsin and alpha-amylase activity compared with those of the control group (P < 0.05). More-over, the liver antioxidant capacity showed a significantly linear decrease with increasing dietary EhSBM (P < 0.05), and there was a significantly decrease in fish fed the diet EhSBM50 than those of the control and EhSBM40 groups (P < 0.05). The serum transaminase activity exhibited significantly linear and quadratic increase with increasing dietary EhSBM (P < 0.05). The pro-inflammatory factor mRNA expressions of liver and hindgut were significantly linear up-regulated with increasing dietary EhSBM, and significant differences were observed in fish fed the diet EhSBM50 than those of the control group (P < 0.05). Furthermore, the hindgut morphology index showed significantly linear and quadratic decrease with increasing dietary EhSBM (P < 0.05). The mRNA ex-pressions of hindgut tight junction protein were significantly linear down-regulated with increasing dietary EhSBM (P < 0.05), but no significant difference was found in fish fed the control and EhSBM40 diets (P > 0.05). Meanwhile, there was a significant increase in the relative abundance of Lactobacillaceae and Clostridium butyricum, and a significant decrease of Vibrio and Pseudomonas of hindgut in fish fed three EhSBM diets than those of the control group (P < 0.05). In conclusion, 40% of fishmeal protein could be replaced by EhSBM protein without significantly reducing growth, antioxidant capacity, intestinal health and inducing inflammatory re-sponses. Meanwhile, intestinal microorganism components were significantly improved in fish fed three EhSBM diets.