# Comprehensive evaluation of environment adaptability in wild and captive lenok (Brachymystax lenok): from the perspective of antioxidant capacity, immune response and gut microbiome

## TL;DR

This study compares wild and farmed lenok fish to understand how their gut health and immune systems differ, which could help improve conservation efforts.

## Contribution

The study introduces new insights into the adaptability of lenok fish through analysis of gut microbiota, immune responses, and intestinal health.

## Key findings

- Wild lenok had longer and denser hindgut villi compared to farmed lenok.
- Wild lenok showed higher hepatic immune and antioxidant activity than farmed lenok.
- Wild lenok had higher Firmicutes and Bacteroidetes abundance in their gut microbiota.

## Abstract

The intestinal microbiota is considered an adaptive trait closely associated with reintroduction success and may contribute to the ecological fitness of B. lenok.

In this study, intestinal morphology, digestive enzyme activity, immune parameters, and gut microbiota composition were compared between wild and farmed B. lenok to elucidate differences in intestinal and hepatic health under distinct aquatic environments.

Histological analysis showed that villi in the hindgut of wild individuals were longer and denser than those of farmed ones. Although the intestinal structure of farmed B. lenok remained intact, their villus morphology and density differed significantly from those of the wild group. Compared with the farmed group, wild B. lenok showed higher hepatic immune/antioxidant activity (elevated alkaline phosphatase (AKP), acid phosphatase (ACP), lysozyme (LYZ), and catalase (CAT), as well as glutathione (GSH) content) and up-regulated liver immune-related genes (c3, foxo1, igM, il-10, lyz, etc.), while farmed fish displayed higher intestinal stress markers (CAT, malondialdehyde (MDA) and a pro-inflammatory signature (il-6, il-1β upregulated). Microbiota profiling revealed higher abundance of Firmicutes and Bacteroidetes but a trend of decreasing Proteobacteria in the wild group.

Collectively, these findings demonstrate significant differences in intestinal morphology, digestive function, and microbial community composition between wild and farmed B. lenok. This study provides new insights for improving post-stocking adaptability in reintroduction programs and proposes novel conservation strategies for biodiversity restoration.