Effects of Dietary Squalene Supplementation on the Growth Performance and Disease Resistance of Largemouth Bass

Feed supplements play a crucial role in improving and maintaining fish health in modern aquaculture practices. Squalene is a functional lipid naturally present in fatty tissues, possessing numerous beneficial biological properties and wide applications in the food and pharmaceutical industries. In this study, the effects of 100 mg/kg (S1), 200 mg/kg (S2), 300 mg/kg (S3), and 400 mg/kg (S4) of dietary squalene supplementation over four weeks on growth performance, antioxidation, hepatoprotection, hypoxia tolerance, immune relative genes expression, and disease resistance of largemouth bass (Micropterus salmoides) were assessed. The results showed that squalene supplementation significantly increased the weight gain rate (WGR) and specific growth rate (SGR) of largemouth bass (p < 0.05). Serum glucose (GLU) levels were significantly decreased in all squalene-supplemented groups (p < 0.05). Squalene supplementation had minimal effect on serum triglyceride (TG) and total cholesterol in (TCHO) levels. A decrease in malondialdehyde (MDA) level, but accompanied by increases in superoxide dismutase (SOD) and hepatic catalase (CAT) activities, was observed in the S1 group supplemented with squalene. These suggest that squalene may mitigate free radical damage and promote health in largemouth bass. Dietary squalene supplementation enhanced intestinal enzyme activities (trypsin, lipase, and α-amylase) in largemouth bass without inducing any apparent hepatic or histopathological alterations. Squalene supplementation improved hypoxia tolerance and antiviral gene expression (mx, ifn-γ, and irf3) while suppressing the expression of inflammatory cytokine (il-1β, il-8, and tnf-α). The survival rate following LMBRaV infection was significantly higher in the S1 group (100 mg/kg group) compared to the control (p < 0.05). In conclusion, this study demonstrated that adding squalene into the diet of largemouth bass at an optimal level of 100 mg/kg effectively promotes growth performance, enhances digestive enzyme activity and hypoxia tolerance, and modulates lipid metabolism and immune gene expression, thereby contributing to improved resistance against LMBRaV. These findings confirm that squalene can serve as a beneficial functional feed additive in aquaculture.