Effects of structurally different starches in high-starch diets on growth, antioxidant status, intestinal immunity, apoptosis, and microbiota composition in largemouth bass (Micropterus salmoides)

This study employed a two-way ANOVA design to investigate the effects of dietary starch level and starch structure on growth performance, antioxidant status, intestinal immunity, apoptosis, and microbiota composition in largemouth bass. Four isonitrogenous and isolipidic diets were formulated by two starch levels (10 %, 20 %) and two starch structures (CS, conventional corn starch; HACS, high-amylose corn starch). Following a 58-day feeding period, results demonstrated that high-starch diets significantly impaired growth parameters (FBW, WGR, SGR) regardless of starch structure. However, HACS-based diets exhibited superior growth performance compared to CS-based diets at both starch levels. Furthermore, dietary high-starch levels reduced hindgut antioxidant capacity, whereas HACS-based diets showed enhanced activities of antioxidant enzymes (CAT, GSH-Px) and lower MDA contents compared to CS-based diets. Histological analysis revealed that CS20 group reduced muscularis thickness and villus height, upregulated the mRNA expression levels of pro-inflammatory ( il-8 , il-1β , nfκb p65 , myd88 ) and pro-apoptotic related genes ( caspase 3 , caspase 7 , baxa , p53 ) compared to the CS10 group, whereas HACS-based groups showed no differences in these gene expression across starch levels and exhibited increased hindgut muscularis thickness compared to CS-based groups. Notably, HACS-based diets demonstrated consistent enhancement of propionate content compared to CS-based diets, independent of dietary starch levels. Moreover, high-starch diets decreased relative abundances of Fusobacteriota (CS10:CS20 =43.72 %:5.13 %; HACS10:HACS20 =79.25 %:48.89 %), Cetobacterium (CS10:CS20 =43.70 %:5.13 %; HACS10:HACS20 =79.25 %:48.87 %), and Cetobacterium somerae (CS10:CS20 =43.70 %:5.13 %; HACS10:HACS20 =79.25 %:48.87 %), while HACS-based groups maintained higher proportions of these microbial taxa compared to CS-based groups regardless of starch levels, and the relative abundances of these bacterial taxa demonstrated significant positive correlations with the propionate concentrations in the intestinal digesta ( R = 0.736, P < 0.01). Overall, under dietary high-starch conditions, HACS-based diets enhanced growth performance, improved intestinal antioxidant capacity, optimized microbial community composition, elevated propionate content in intestinal digesta, and mitigated inflammatory and apoptotic responses compared to CS-based diets in largemouth bass. • HACS counteracts the growth suppression induced by CS in largemouth bass under high-starch diets. • HACS diets optimized intestinal microbiota, improved intestinal immunity and reduced apoptosis compared to CS diets. • HACS diets elevated propionate contents in intestinal digesta compared to CS diets.