Comparison of dehulled, fermented and enzyme-treated soybean meal in diets for largemouth bass, Micropterus salmoides: Effects on growth performance, feed utilization, immune response and intestinal morphology

A 67-day feeding trial was conducted to evaluate the nutritional value of dehulled soybean meal (DSM), fermented soybean meal (FSM), and enzyme-treated dehulled soybean meal (EDSM) in diets prepared for cultured largemouth bass (Micropterus salmoides). Triplicate groups of fish were fed diets composed of different soybean meal twice daily. The results showed that the inclusion of EDSM led to the best specific growth rate (SGR), while the SGR of fish fed with soybean meal fermented by a mixture of microorganisms (Lactobacillus bulgaricus, Saccharomyces cerevisiae, and Bacillus subtilis) (FSMI) was significantly higher than that of fish fed with soybean meal fermented with Saccharomyces cerevisiae (FSMII), and with untreated soybean meal. Moreover, DSM resulted in the lowest apparent digestibility coefficient of protein and lipid, which may account for the observed reduction in the feed efficiency ratio and protein efficiency ratio as well as the impaired growth performance. The fish fed the diet with DSM exhibited the lowest protein retention rate but the highest lipid retention rate, which may be related to the variation in body composition in combination with feed utilization. The activity of lysozyme and classical complement pathway in fish fed diets with EDSM and FSMI was significantly higher than that in the DSM group, and the DSM group also produced the lowest hematological index value. Moreover, specific histo-pathological changes were observed in distal intestine of fish fed the diet with DSM. The results showed that fermentation and enzymatic pre-processing can improve the nutritional value of soybean meal, possibly be reducing anti-nutritional factors. For largemouth bass, the EDSM performed better than FSM in elevating growth performance and feed utilization under the ap-plied experimental conditions.