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

Abstract

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\>0.05). Fish fed diets MRY1 and MRY1.5 had lower serum alanine aminotransferase (ALT) content than the MRY0 and MRY0.5 groups (P<0.05). Serum glucose (GLU) content showed an increasing trend with increasing MRY levels, and the MRY1.5 group had the highest value (P<0.05), while cholesterol (TC) and triglyceride (TG) levels exhibited an opposite trend, and fish-fed diet MRY1 had lowest values (P<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<0.05). Hepatic total superoxide dismutase (T-SOD) and serum alkaline phosphatase (ALP) activities increased with the increase of dietary MRY level (P<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<0.05), and no significant difference was found in the relative expression of HSP90 in the liver among all groups (P\>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.