Dietary succinic acid mitigates adverse effects of starch high-starch diet in largemouth bass (Micropterus salmoides) through gut-liver axis modulation

Abstract

A 10-week feeding trial was conducted to investigate the effects of succinic acid (SUA) supplementation in high-starch diets (HSD) on growth and enterohepatic health of largemouth bass (Micropterus salmoides; initial weight 11.96 ± 0.71 g). Six isocaloric and isolipidic diets were formulated, comprising a standard diet containing 10% corn starch and 40% fish meal, an HSD with 15% corn starch and 36% fish meal, and HSDs supplemented with 0.5%, 1.0%, 1.5%, and 2.0% SUA. Compared to standard diet, HSD exhibited adverse effects including impaired feed utilization, growth retardation, diminished antioxidant capacity, and immune response, along with metabolic dysregulation and gut microbiota disturbances. Significant linear and quadratic dose-responses were detected for multiple parameters: feed conversion ratio, hepatosomatic index, viscerosomatic index, glycogen content, amylase and protease activities, and hepatic antioxidant status. The 0.5% SUA supplementation group demonstrated enhanced intestinal morphology, upregulated expression of tight junction proteins (ZO-1 and Claudin-4) and antiapoptotic Bcl2, increased abundance of beneficial microbiota and suppressed endoplasmic reticulum stress markers (GRP78, PERK, IRE1, ATF6, eIF2α, and Chopα). Additionally, dietary 0.5% SUA upregulated hepatic anti-inflammatory mediators (Nrf2, TGFβ1, and IL10), glycolytic genes (PK, PFKL2, and GK), β-oxidation-related CPT1, antiapoptotic Bag, and glucose transporter GLUT2, while downregulating proinflammatory TNFα, gluconeogenic enzymes (PEPCK and G6Pase), lipogenic genes (ACC1 and FASN), and proapoptotic Bad. Broken-line regression analysis identified 0.46-0.50% as the optimal SUA inclusion level based on growth parameters. This study demonstrates that appropriate SUA supplementation alleviates HSD-induced oxidative stress, enhances intestinal barrier function, modulates gut microbiota, and maintains metabolic homeostasis, thereby improving starch utilization and growth performance.

Keywords: Enterohepatic health; Glucolipid metabolism; High-starch diet; Succinic acid.