Dietary poly‐β‐hydroxybutyrate supplementation can effectively improve growth, digestive enzyme activities, immune‐related gene expression, disease resistance, and intestinal mucosal barrier of gibel carp, <i>Carassius auratus gibelio</i>

Poly-β-hydroxybutyrate (PHB) can promote growth and enhance immunity of aquatic animals such as gibel carp, Carassius auratus gibelio. However, the optimal dietary supplementation level feeding duration for carp are still unclear. In this study, effects various PHB levels on performance, digestive enzyme activities, immune function, disease resistance, intestinal mucosal barrier were evaluated. Six experimental diets differing in formulated, that is, 0% (P0 control), 0.5% (P0.5), 1% (P1), 2% (P2), 4% (P4), 8% (P8). Results indicated promoted fish performance significantly (p < 0.05). Compared to control group P0, lipase, protease, amylase activities P4 increased after 30 days Meanwhile, at 60 upregulated mRNA expression immune-related genes, including IL-11, ITLN, MPO, KRT-8, DUSP-1, PNP-5α 0.01). Furthermore, showed positive resistance against both viral bacterial infections exerted beneficial maintaining epithelial integrity. conclusion, or was recommended culture.