Effects of Dietary Chitin Inclusion on Growth Performance, Intestinal and Hepatic Health, and Muscle Texture in Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

Antarctic krill (Euphausia superba) meal is a valuable aquafeed ingredient, but its chitin-rich exoskeleton may limit nutrient utilization. A 12-week trial evaluated fishmeal-based diets containing 0, 1.5%, 3.0%, or 6.0% chitin in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). Dietary chitin did not significantly affect survival or growth. However, feeding rate and feed conversion ratio initially increased and then decreased, while protein efficiency ratio declined at all supplemented levels. At 1.5%, intestinal chitinase activity and IL-1β, TNF-α, and IL-6 were reduced. At ≥3.0%, serum T-BIL content, AST and ALT activities, AST/ALT ratio, plasma LPS content and DAO activity increased, whereas intestinal MPS, LZM, IgM, TGF-β1, IFN-γ, and IL-8 decreased. At 6.0%, lipase activity was further reduced. Some hepatic immune markers declined at 1.5% dietary chitin, while others decreased only at higher levels. In contrast, IL-10 increased at ≥3.0%, indicating altered hepatic immune homeostasis rather than generalized immunosuppression. Hepatic antioxidant capacity decreased at 6.0%. Dietary chitin ≥ 1.5% also reduced muscle hardness, gumminess, and chewiness. These findings indicate that even at the lowest tested inclusion level (1.5%), dietary chitin affected feed utilization and muscle texture, highlighting the need for further investigation of inclusion levels below 1.5%.