Effects of fishmeal substitution by four fermented soybean meals on growth， antioxidant capacity and inflammation responses of turbot juveniles (Scophthalmus maximus L.)

A 10-week feeding trial was conducted to examine the effects of fishmeal (FM) substitution by different types of FSBM on growth performance, antioxidant capacity and inflammatory responses of turbot juveniles ( Scophthalmus maximus L.). Four strains of microorganisms Saccharomycopsis fibuligera isolate Y27 (SF), Bacillus tequilensis KCTC 13622 (BT), Bacillus subtilis strain D7XPN1 (BS) and Bacillus aryabhattai B8W22 (BA) with high-efficiency degradation of glucoside of soybean isoflavones (SI) were obtained through screening and isolation, and were used to ferment soybean meal (SBM) to enhance the utilization of SBM. Six isonitrogenous (50.05% crude protein) and isolipidic (10.46% crude lipid) diets were formulated. The FM diet (the control diet) was formulated with 55% fishmeal. Five experimental diets (Diets SBM45, SF45, BT45, BS45 and BA45) were formulated by replacing 45% of FM inclusion level of control diet using SBM or either FSBM produced by the above four strains, respectively. Results showed that there was a significant decrease in feed intake (FI) of fish fed the SBM45 diet than those of the control and either FSBM diets ( P = 0.000), and no significant difference was found among the control, SF45, BT45 and BS45 groups ( P > 0.05). Meanwhile, fish fed the diet BA45 showed a significantly higher FI compared with the control group ( P = 0.000). The appetite-stimulating factor (agouti gene-related protein, agrp1 ) gene expression was significantly up-regulated in fish fed the diet SF45 compared with the SBM45 group ( P = 0.058). Meanwhile, the appetite-suppressive factors (proopiomelanocorein, pomc and cocaine and amphetamine regulated transcript, cart ) gene expression was significantly down-regulated in fish fed the diet SF45 compared with the SBM45 group ( P = 0.009, 0.006). The foregut α-amylase and trypsin activity were significantly promoted in fish fed the diet BS45 compared with those of the SBM45 and BA45 treatments ( P = 0.000). There was a significant decrease in apparent digestibility coefficient of dry matter in fish fed the SBM45 diet compared with fish fed the control diet and fish fed either FSBM-based diet ( P = 0.000), however, no significant difference was found among the control, SF45, BS45 and BA45 groups ( P > 0.05). Moreover, no significant difference was observed in survival rate among dietary treatments ( P > 0.05). Fish fed the diet BT45 had significantly lower feed efficiency than that of the control group ( P = 0.048), meanwhile no significant difference was found among the control, SBM45, SF45, BS45 and BA45 treatments ( P > 0.05). Fish fed the SBM45 diet had significantly lower specific growth rate compared with fish fed the control diet and fish fed either FSBM-based diet ( P = 0.000). Furthermore, the antioxidant capacity significantly increased in fish fed the control and four FSBM diets compared with the SBM45 group ( P < 0.05). The serum, liver and hindgut inflammatory responses of fish fed the control and four FSBM diets were significantly lower than those of the SBM45 group ( P < 0.05). In conclusion, fish fed four FSBM diets could promote growth, enhance antioxidant capacity and reduce inflammatory responses of turbot juveniles compared with those of the SBM45 group. • Four strains were screened based on the degradation rate of genistin for the first time and applied to the solid-state fermentation of SBM. • The glucoside of soybean isoflavones in SBM were significantly degraded with the four strains fermentation. • Fish fed four FSBM diets could significantly promote growth, enhance antioxidant capacity and reduce inflammatory responses of turbot juveniles.