Effect of yeast cell wall on growth performance, antioxidant capacity and expression of immune-related genes in Micropterus salmoides

In order to investigate the effect of commercial yeast cell wall extract (YCW) on growth performance and health status of Micropterus salmoides. Using M. salmoides with an initial weight of (10.34 ± 0.35) g as the subject, YCW was added at 0, 2, 4, 6, and 8 g/kg to the basic feed, and the groups were labeled as YCW0, YCW2, YCW4, YCW6, and YCW8 respectively. A 56-day aquaculture experiment was conducted. The results showed that YCW6 group had the greatest weight gain rate (WGR), which was 10.45% higher than that of YCW0 group. The feed coefficient (FCR) was significantly lower than that of YCW0 group when the YCW addition exceeded 0.2%. With the increase of YCW addition, the hepatosomatic index (HSI) and viscera weight index (VSI) showed fluctuating changes. There was no significant difference in the survival rate (SR) and condition factor (CF) among the groups; the results of whole fish body composition showed that YCW addition significantly increased the crude protein content of whole fish, but had no significant effect on ash and crude lipid; the results of antioxidant and immune indexes showed that, compared with the YCW0 group, the YCW6 group significantly increased the activities of catalase (CAT), superoxide dismutase (SOD), acid phosphatase (ACP), and alkaline phosphatase (AKP) of the M. salmoides, as well as the total antioxidant capacity, and the YCW8 group significantly increased lysozyme activity (LZM); the results of immune-related genes showed that with the increase of YCW addition, the expression of tnf-α gene in liver, spleen, kidney and gill, and the expression of tgf-β1 gene in kidney showed a tendency of decreasing and then increasing, and there was no significant effect on the expression of tgf-β1 gene in liver, gill and spleen among the groups. The expression of il-10 gene was significantly higher in liver and kidney in YCW6 and YCW8 groups than in YCW0 group, but there was no significant effect on the expression of il-10 gene in spleen and gill. hsp70 expression was significantly up-regulated in liver (YCW4 and YCW6 groups) and spleen (YCW8 group), but significantly down-regulated in kidney. Based on the quadratic curve regression analysis of weight gain rate, the optimal amount of YCW in M. salmoides diets was determined to be 5.40 g/kg, and the addition of YCW significantly promoted the growth of M. salmoides, enhanced the antioxidant capacity, and enhanced the non-specific immunity and regulated the expression of key immune genes, thus improving its overall health condition. This study provides a basis for the scientific application of YCW in M. salmoides feed.