Effects of Rice-Field and Pond Culture Systems on the Nutritional Quality, Metabolomic Profiles and Intestinal Microbiota of Largemouth Bass (Micropterus salmoides)

As aquaculture production becomes increasingly quality-oriented, understanding how culture systems affect the nutritional characteristics of edible fish muscle is important for evaluating aquaculture products. In this study, growth performance, muscle amino acid and fatty acid composition, metabolomic profiles and intestinal microbiota were compared between largemouth bass (Micropterus salmoides) reared in a rice-field culture system (MR) and a conventional pond system (MP). Overall growth performance was comparable between the two systems, although MR fish exhibited a higher condition factor. Total hydrolyzed amino acid contents were comparable between the groups, whereas differences in several free amino acids suggested distinct potential taste-related characteristics of the edible muscle. MP fish contained higher amounts of total fatty acids, saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, n-3 PUFA, EPA and DHA, whereas MR fish exhibited a higher n-3/n-6 PUFA ratio. Muscle metabolomic profiles also differed between the two systems, particularly for metabolites associated with amino acid, purine and lipid metabolism. In addition, MR and MP fish exhibited distinct intestinal microbial communities, with higher microbial richness in MR fish and different dominant bacterial taxa between the systems. Overall, the rice-field culture system represents a promising ecological alternative for largemouth bass production because it maintained growth performance comparable to pond culture while producing a distinct edible-muscle nutritional profile, including a higher n-3/n-6 PUFA ratio. Pond-cultured fish, however, contained higher absolute amounts of several nutritionally important fatty acids, including n-3 PUFA, EPA and DHA. The distinct intestinal microbial communities observed between the systems further indicate different gut ecological responses to the two culture environments.