Microbiomic and metabonomic analysis provide new insights into the enhanced intestinal health in large-size largemouth bass (Micropterus salmoides) when fed novel proteins: Novel proteins are promising foods for future aquaculture

The novel proteins, i.e., Clostridium autoethanogenum (CAP), Tenebrio molitor (TM), Chlorella vulgaris (ChM), and cottonseed protein concentrate (CSM), are promising food for the future aquaculture due to the limited fishmeal (FM) resources. However, in-depth investigations on the intestinal barriers of fish when fed novel proteins are sparse, and the association between intestinal flora and physiological biomarkers is still unknown. Five isonitrogenous and isolipidic diets comprising various proteins were developed, with fishmeal serving as the control and novel proteins as the experimental diets. Largemouth bass (Micropterus salmoides) with an initial body weight of 211.9 ± 1.2 g were used as experimental model and fed with these five diets for eight weeks. The findings from the current study indicated that the intestinal histological structure as well as immunochemistry barrier performance of the ChM, CAP, and TM groups were superior to those of the CSM and FM groups, despite the fact that the villi height of FM was the greatest of all groups. Similarly, the intestinal inflammatory response and the permeability were elevated in CSM while decreased in ChM, CAP, and TM group. Concerning the intestinal short fatty acids (SCFAs), the levels in the CAP as well as ChM group were greater than the other proteins. From the data analysis of 16S rRNA gene sequencing, the abundance of opportunistic pathogens including (Ralstonia, Acinetobacter, Aeromonas, and Protebacteria) were higher in CSM group while attenuated in ChM, CAP and TM group. In addition, the abundance of nine types of intestinal-barriers-repairing probiotics were elevated in all novel proteins compared with the fishmeal group. These altered microbiota were highly correlated with intestinal inflammatory response, antioxidant status, immunochemistry barrier, physical barrier and SCFAs indexes by Mantel test and Pearson's correlation analysis. Collectively, the ranking of the beneficial functions among these five proteins was ChM > CAP>TM > FM > CSM according to Z-score and this study provides in-depth data manifesting the effects of novel proteins on the gut health status of large-size largemouth bass.