Effects of dietary fishmeal replacement with Periplaneta americana meal on growth, antioxidant activity, and immunity of juvenile largemouth bass, Micropterus salmoides.

At present, the aquaculture industry is experiencing a significant rise in fishmeal (FM) demand due to the growth of breeding scale and factory aquaculture, which seriously impedes the sustainable development of aquaculture. Insect meal has become a key option for partially substituting FM in aquafeed. The study investigated how substituting FM with (Periplaneta americana meal (PAM) impacts the growth performance, body composition, antioxidant activities, digestive enzyme activity, and immunity in juvenile largemouth bass (JLMB). Four hundred and fifty JLMB, averaging 16.71 ± 0.09 g in starting weight, were selected for an 8-week feeding experiment. The experimental diets were prepared by substituting FM in the basal diet with PAM at five concentration levels: 0% (P0, control), 5% (P5), 10% (P10), 15% (P15), and 20% (P20). Results showed that weight gain rate (WGR) and specific growth rate (SGR) were not significantly different among JLMB across all experimental groups (P > 0.05). In P20, a significant increase in the feed conversion ratio (FCR) was observed, along with a significant decrease in the viscerosomatic index (VSI) (P < 0.05). As the concentration of PAM increased, a significant decrease in the hepatosomatic index (HSI) was observed (P < 0.05). The activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in the liver and gut were significantly elevated compared to those in P0 (P < 0.05). The intestinal morphological structure exhibited no significant alterations (P > 0.05). The activities of pepsin and lipase in the intestines significantly increased with the increasing concentration of PAM (P < 0.05). In comparison with P0, P15 had significantly lower expression of IL-8 and TNF-α (P < 0.05), yet significantly higher expression of IL-10 and HIF-1α (P < 0.05). Collectively, our study demonstrated that using PAM as a substitute for FM did not have a negative impact on the growth of JLMB and improved antioxidant activity and immune response.