Effects of Hydrogen-Rich Water on Juvenile Largemouth Bass (Micropterus salmoides) Under Acute Low-Temperature Stress

Hydrogen-rich water (HRW) is an aqueous solution containing dissolved molecular hydrogen. This study evaluated its effects on juvenile largemouth bass (Micropterus salmoides) under acute low-temperature stress. A total of 480 juveniles (2.4 ± 0.5 g) were randomly assigned to four groups: the control group was reared in standard water; the treatment groups were exposed to different hydrogen concentrations, specifically H1 (0.3 mg/L), H2 (0.5 mg/L), and H3 (0.9 mg/L). The fry were reared at 26 ± 0.5 °C for 30 days, followed by acute low-temperature stress (11 ± 0.5 °C) for 48 h. Samples were collected at 0, 8, 24, and 48 h. Results showed that after 30 days of HRW rearing, the final body weight (FBW), specific growth rate (SGR), and condition factor (CF) of the H1 group were significantly increased, while the H3 group only increased CF. No significant differences were observed in hepatopancreas somatic index (HSI) and survival rate (SR) among groups. Acute low-temperature stress induced liver and intestinal damage, which were alleviated in the H1 group. The H1 group exhibited significantly increased SOD, CAT, and GSH-Px activities in the liver, as well as CAT and SOD in the intestine and gills, while reducing MDA levels, thereby enhancing the antioxidant capacity. The H1 group significantly upregulated the antioxidant genes expression (sod, cat, and gsh-px mRNA levels) in the liver and gills but downregulated them in the intestine. 16S rDNA analysis revealed that HRW increased intestinal microbiota and the relative abundance of Bacillota. In conclusion, the H1 group significantly improved growth performance, mitigated acute low-temperature damage, enhanced antioxidant capacity, and increased the relative abundance of Bacillota in the intestines. This provides an innovative, safe, and effective solution for aquaculture industries confronting low-temperature challenges.