Mulberry (Morus alba) leaves improved the growth and intestinal health in largemouth bass (Micropterus salmoides) fed a cottonseed protein concentrate-based diet

Mulberry leaves (ML) have diverse biological activities and show potential as a functional additive. However, it is unclear whether ML can alleviate the adverse effects of high cottonseed protein concentrate (CPC) inclusion in carnivores. In this study, Micropterus salmoides were respectively fed six different diets over an 8-week period. Four experimental diets were formulated with varying levels of ML (0%, 2%, 4%, and 6%), designated as CG (basic diet), ML2, ML4, and ML6. Additionally, two diets replaced 75% of fishmeal (FM) protein with CPC in the CG diet, with or without 4% ML, named CPC and CM4 diet, respectively. Results showed that ML4 diet improved growth and feed utilization in largemouth bass compared with the control. The growth of fish fed with the CPC diet were significantly lower than those fed with the CG diet (P < 0.05). However, supplementing 4% ML in the CPC diet could improve the decreased growth and feed utilization, compromised intestinal barrier, and intestinal inflammation caused by high CPC in largemouth bass. Through 16S rDNA and intestinal transcriptome correlation analysis, it was revealed that ML could reduce non-homeostatic apoptosis by positively regulating intestinal microbiota to down-regulate the expression of pro-apoptosis genes in the PI3K-Akt pathway of the Apoptosis pathway.