Evaluation of Squalene for Growth Performance and Disease Resistance of Largemouth Bass (Micropterus Salmoides)

Abstract

Dietary supplement feed additive is an effective approach to promote fish health in aquaculture. Squalene (SQU), a functional lipid found in fatty tissues, possesses numerous beneficial biological functions and has been widely used. In this study, the growth performance, antioxidation, liver protection, hypoxia tolerance, immune relative genes expression, and disease resistance of Largemouth bass were all examined in relation to different levels of dietary squalene supplementation (0, 100, 200, 300, and 400 mg/kg feed) for four weeks. The results showed Largemouth bass treated with squalene increased in weight gain rate (WGR) and specific growth rate (SGR). Serum total protein (TP) level was increased, while serum glucose (GLU) activity was significantly decreased in all squalene addition groups. Triglyceride (TG) level and total cholesterol (TCHO) in serum and liver displayed a decreasing trend. The malondialdehyde (MDA) level dropped, but superoxide dismutase (SOD) and hepatic catalase (CAT) activities increased in squalene treated groups, which these indicated that squalene could alleviate free radical damage and improve largemouth bass health to a certain extent. The trypsin, lipase and α-amylase activities of intestinal were all elevated as squalene addition. The histopathological examination demonstrated that squalene caused no damage to liver and intestinal in largemouth bass. Hypoxia tolerance tests indicated an improved oxygen-carrying capacity in squalene addition groups. Squalene decreased the expression of cytokines that induced inflammation (IL-1β, IL-8, and TNF-α) and increased the expression of antiviral genes (Mx, IFN-γ, and IRF3). The survival rates of largemouth bass infected with largemouth bass ranavirus (LMBRaV) was significantly improved after the dietary addition squalene. In conclusion, all the results obtained in this study revealed that the squalene addition in diety of largemouth bass can accelerate growth performance, enhance enzyme activity, facilitate hepatic lipid metabolism and intestinal digestion, improve hypoxia tolerance and increase immune relative genes expression, as well as strengthen the resistance to LMBRaV in largemouth bass. These highlight the squalene’s potential as a valuable dietary supplement in aquaculture. The optimal squalene addtion level was identified as 100 mg/kg feed.

Keywords: Largemouth bass, Squalene, Growth performance, Antioxidation, Disease resistance