Effects of alternate feeding between fish meal and novel protein diets on the intestinal health of juvenile largemouth bass (Micropterus salmoides)

Abstract

To investigate the possibility of completely replacing dietary fish meal with several novel proteins in largemouth bass (Micropterus salmoides), the intestinal health of largemouth bass switched to novel protein diets after being fed with fish meal diet for a certain time were examined. The novel proteins included Chlorella vulgaris (ChM), Clostridium autoethanogenum (CAP), and cottonseed protein concentrate (CSM). The four isonitrogenous and isoenergetic diets containing different proteins were formulated. Fish meal diet was fed to experimental fish with an initial body weight of 4.99 ± 0.19 g for the first four weeks and then fed each single protein diet for another four weeks. The results suggested that the fish meal group as well as ChM group had a higher villi height and width than the other two novel proteins. The intestinal superoxide dismutase activity was significantly decreased in CSM and ChM but significantly enhanced in CAP, while the intestinal malondialdehyde level was significantly raised in CSM (P < 0.05). Furthermore, CSM up-regulated intestinal inflammation by significantly increasing pro-inflammatory cytokine expression and decreasing anti-inflammatory cytokine expression (P < 0.05). In comparison, CAP and ChM down-regulated the intestinal inflammation and enhanced intestinal barrier integrity showing by the increased expression of marker genes (P < 0.05). The intestinal microbiota, as determined by high-throughput sequencing, revealed a rise in the abundance of pathogenic bacteria taxa (Proteobacteria, Acinetobacter) in CSM. In contrast, the abundance of beneficial bacteria taxa (Firmicutes, Bacteroidetes, and Cetobacterium) was increased in CAP and ChM. In conclusion, ChM and CAP benefited largemouth bass intestinal health by raising the activity of intestinal antioxidant enzymes, suppressing the inflammatory response, strengthening the intestinal barrier, and boosting the quantity of beneficial bacteria. CSM impaired largemouth bass intestinal health by decreasing antioxidant enzymes activities, increasing the inflammatory response as well as the abundance of pathogenic bacteria taxa.