Effects of dietary marine red yeast on growth performance, digestive enzyme activities, antioxidant capacity, and immunity response of white-spotted conger ( <i>Conger myriaster</i> )

This study aimed to investigate the effects of marine red yeast (MRY) on growth performance, digestive enzyme activities, serum biochemistry, antioxidant capacity, immunological indices, and expression of immune-related genes in white-spotted conger ( Conger myriaster ). Four diets were supplemented with varying levels of MRY (0%, 0.5%, 1.0%, and 1.5%, designated as MRY0, MRY0.5, MRY1, and MRY1.5, respectively). Fish (average weight, 46.27 g) were divided into 12 net cages, with 3 cages per diet. The fish were fed diets twice daily for 56 days. Results indicated that dietary supplementation of MRY had no significant effects on growth and digestive enzyme activities ( P &gt;0.05). Fish fed diets MRY1 and MRY1.5 had lower serum alanine aminotransferase (ALT) content than the MRY0 and MRY0.5 groups ( P &lt;0.05). Serum glucose (GLU) content showed an increasing trend with increasing MRY levels, and the MRY1.5 group had the highest value (P&lt;0.05), while cholesterol (TC) and triglyceride (TG) levels exhibited an opposite trend, and fish-fed diet MRY1 had lowest values ( P &lt;0.05). Fish fed diet MRY0.5 had significantly higher hepatic glutathione peroxidase (GSH-Px) activity than those fed diets MRY0 and MRY1.5 ( P &lt;0.05). Hepatic total superoxide dismutase (T-SOD) and serum alkaline phosphatase (ALP) activities increased with the increase of dietary MRY level ( P &lt;0.05). Fish fed diet MRY1.5 exhibited significantly lower relative expression of heat shock protein 70 ( HSP70 ) in the liver than fish fed diets MRY0 and MRY0.5 ( P &lt;0.05), and no significant difference was found in the relative expression of HSP90 in the liver among all groups ( P &gt;0.05). In conclusion, 1%–1.5% MRY could be applied as a feed additive to effectively enhance the immune response of white-spotted conger.