Effects of dietary Hericium erinaceus powder on growth, hematology, disease resistance, and expression of genes related immune response against thermal challenge of Nile tilapia (Oreochromis niloticus)

Functional feed additives have been promising possibilities for improving fish immune function. The present study attempts to investigate the effect of dietary Hericium erinaceus (HE) supple-mentation on growth performance, hematology, disease resistance, and expression of genes related immune response against thermal challenge in Nile tilapia. Four isonitrogenous and isolipidic diets were prepared: a control diet without HE supplementation (HE0), HE supple-mentation at 5 g/kg (HE5), 10 g/kg (HE10), and 20 g/kg (HE20). Each diet was fed to quadru-plicate groups of Nile tilapia (9.96 +/- 0.01 g/fish) to apparent satiation two times daily for 10 weeks. The dietary HE supplementation promoted protein productive value with a quadratic effect (P = 0.002) although it had no significant effect on other growth and feed utilization pa-rameters (P > 0.05). In addition, the dietary HE supplementation linearly increased red blood cell count, hematocrit, and hemoglobin content (P & LE; 0.001) and quadratically increased the contents of protein and albumin, as well as the alkaline phosphatase activity (P < 0.05). The aspartate Animal Feed Science and Technology 290 (2022) 115342 aminotransferase activity was linearly and quadratically decreased (P = 0.037, 0.017), and the plasma cortisol level was linearly decreased by increasing HE levels (P = 0.001). The microbial resistance of Nile tilapia against Streptococcus agalactiae increased in all HE-supplemented groups compared to the control group in association with the significant increases in hepatic mRNA levels of genes related immunity, including TNF-alpha, IL-1 beta, IL-6, IL-10, and TGF-beta. The dietary HE supplementation did not significantly affect the pre-thermal challenge expression of HSP70cB1 mRNAs (P > 0.05), but significantly decreased HSP70cB1 transcripts and plasma cortisol levels after thermal stress challenge (P < 0.05). Therefore, it is suggested that HE at 10 g/kg can be used as a feed additive that enhances the immunity response, reduces the risk of infectious diseases caused by S. agalactiae, and improved thermal stress resistance in Nile tilapia culture.