Effects of salinity stress on the growth performance, health status, and intestinal microbiota of juvenile Micropterus salmoides

Abstract

Soil salinization has become a increasingly serious problem due to the continuous deterioration of the global environment. A large amount of land is unused due to salinization, and this represents a large waste of resources. Micropterus salmoides is a freshwater fish that has become increasingly popular among consumers in recent years. We investigated the effects of salinity stress on the growth performance, health status, and intestinal microbiota of juvenile M. salmoides. >480 juveniles were reared in tanks at salinity levels of 0, 5‰, 10‰, and 15‰ for 6 weeks. The weight gain rate and specific growth rate significantly decreased as salinity increased. Superoxide dismutase (SOD) activity significantly increased in the 5‰ salinity group. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), acid phosphatase (ACP), alkaline phosphatase (AKP) activity and total antioxidant capacity (T-AOC) significantly increased when the salinity was 15‰ (P < 0.05).Catalase (CAT), and glutathione peroxidase (GSH-PX) activity was highest in the control group. This indicates that 5‰ salinity can enhance the immune function of M. salmoides. However, excessive salinity can damage the immune system of M. salmoides. Paraffin sections of intestinal tissue revealed that villus length decreased and the magnitude of epithelial cell expansion increased as salinity increased. According to intestinal microbiota analysis, the dominant intestinal microbial taxa in M. salmoides were altered in saline environments. The abundance of Bacillus was significantly increased at a salinity of 10‰. Clusters of Orthologous Groups enrichment analysis revealed that salinity stress mainly affected lipid metabolism and amino acid metabolism. We also identified an important pathway called republication recombination and repair that was significantly enriched in the 15‰ salinity group. This indicates that the normal life activities of M. salmoides were maintained under a saline environment via the regulation of amino acid metabolism and lipid metabolism, as well as the salinity stress response mechanism. In sum, M. salmoides can survive normally at a salinity <5‰. It could thus be used as a saline–alkaline culture species. The results of our experiment provide new insights into the salinity tolerance of freshwater fish and will enhance the use of saline–alkaline land.