Characteristics and differences in immune response capacity and gut microbiome between wild and captive Amur grayling (Thymallus grubii): New insights into endangered fish conservation

Cunhua Zhai¹Ziyang Wang²Luye Bai³Haoxiang Han⁴Bo Ma^1*

• ¹Heilongjiang River Fishery Research Institute of Chinese Academy of Fishery Sciences, Harbin, China
• ²Harbin Normal University, Harbin, China
• ³Dalian Ocean University, Dalian, China
• ⁴Heilongjiang River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Heilongjiang, China

Endangered species recovery hinges on evaluating captivity-induced shifts in the adaptive traits of candidates slated for reintroduction. Gut microbiota is one such trait and is particularly important for Amur grayling (Thymallus grubii). The present study aimed to systematically investigate the differences in intestinal and liver health in Amur grayling from two water environments (wild and captive) by feeding habits, biochemical parameters and 16S ribosomal RNA gene sequencing. Compared with captive fish, the wild Amur grayling in the liver and gut had higher lysozyme activity (P < 0.05), and alkaline phosphatase, catalase activity and glutathione content in gut was significantly higher (P < 0.05). In addition, the cultured fish showed lower relative expression levels of hepatic IgM, il-6, il-10, il-lβ, myd88, NF-kB, and Tnf-α mRNA expressions than those of wild fish (P < 0.05). In the intestine tissue, the mRNA level of C3, il-6, il-10, il-lβ, tlr1, tlr3, Tnf-α, and LYZ increased in the wild fish while the expression of IgM was significantly elevated (P < 0.05). For gut microbiota, the cultured group displayed higher percentages of Pseudomonadota phylum and lower percentages of Bacillota phylum than the wild group (P < 0.05). Overall, wild Amur grayling had higher immune capacity and intestinal barrier functions than cultured Amur grayling. This study displayed that responses and adaptations to diverse aquatic environments were shown by liver-gut-microbiota axis in Amur grayling. Our findings could provide a promising direction for the improve its adaptability of wild population in reintroduction project and propose the conservation strategy for biodiversity recovery.