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.)

Abstract

An 8-week feeding trial was conducted to study the effects of fishmeal substitution by different levels of α-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 α-amylase activity exhibited significantly linear decrease with increasing dietary EhSBM (P < 0.05). Fish fed diets EhSBM45 and EhSBM50 exhibited significantly lower trypsin and α-amylase activity compared with those of the control group (P < 0.05). Moreover, 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 expressions 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 responses. Meanwhile, intestinal microorganism components were significantly improved in fish fed three EhSBM diets.