Effects of Crayfish Shell Meal Processing Methods on Growth Performance, Antioxidant Capacity, Intestinal Function and Gut Microbiota of Largemouth Bass (Micropterus salmoides)

Simple SummaryCrayfish processing produces large amounts of shell by-products that could be used in aquafeeds, but their direct use is limited by poor digestibility and high chitin and ash contents. This study compared dried, enzymatically hydrolyzed, and fermented crayfish shell meals as partial replacements for fish meal in diets for juvenile largemouth bass. Dried crayfish shell meal reduced growth and caused less favorable intestinal and physiological responses. In contrast, fermented crayfish shell meal maintained growth performance comparable to the fish meal control and improved antioxidant status, intestinal enzyme activity, and gut microbiota. Enzymatic hydrolysis showed partial benefits but was less effective than fermentation. These results suggest that fermentation is a useful strategy for improving the feeding value of crayfish shell by-products and converting them into sustainable aquafeed ingredients.This study evaluated the effects of crayfish shell meal (CSM) processed by drying, enzymatic hydrolysis, or fermentation on juvenile largemouth bass (Micropterus salmoides). A total of 320 fish (initial body weight, approximately 5.69 g) were distributed into 16 tanks, with 20 fish per tank and four replicates per treatment. Four isonitrogenous and isoenergetic diets were prepared: a fish meal-based control diet (FM) and three diets containing 4.5% dried CSM (DCSM), enzymatically hydrolyzed CSM (ECSM), or fermented CSM (FCSM), in which fish meal was reduced from 45.0% to 39.6%, and were fed for 8 weeks. Compared with the FM group, DCSM significantly reduced final body weight, weight gain rate, specific growth rate, and protein efficiency ratio, and increased feed conversion ratio (p< 0.05). ECSM generally showed intermediate responses, whereas FCSM did not differ significantly from FM in these growth and feed utilization indices (p> 0.05). DCSM also significantly increased serum aspartate aminotransferase and blood urea nitrogen levels and induced a pro-inflammatory intestinal response, as indicated by decreasedil10and increasedil1bandtnfaexpression (p< 0.05). Compared with DCSM, FCSM significantly improved these serum and inflammatory indices, increased intestinal trypsin, Na+/K+-ATPase and γ-glutamyl transferase activities (p< 0.05), and showed more favorable antioxidant and gut microbiota responses. Overall, fermentation was more effective than enzymatic hydrolysis in improving the feeding value of CSM for largemouth bass. These results suggest that FCSM is a promising alternative ingredient for aquafeeds and may contribute to the high-value utilization of crayfish processing by-products.