Effects of NaHCO ₃ Alkalinity Stress on <i>Micropterus salmoides</i>

ABSTRACT To provide guidance for the actual cultivation of Micropterus salmoides in saline alkali environment, the effects of NaHCO 3 alkalinity stress on enzymatic activity, tissue structure and gut microbiota were investigated. The experimental groups consisted of Group 1 (no NaHCO 3 added), Group 2 (10 mmol/L NaHCO 3 alkalinity) and Group 3 (30 mmol/L NaHCO 3 alkalinity). Samples were taken on Day 10. The results showed that Group 1 had higher superoxide dismutase (SOD), acid phosphatase (ACP) and alkaline phosphatase (AKP) activities and lower malondialdehyde (MDA) levels, however, Group 3 had lower SOD, ACP and AKP activities and higher MDA levels. Besides, stress with NaHCO 3 alkalinity caused histological damage to the liver and gills, and with the increase of stress concentration, the swelling, vacuolization and nuclear shift of liver cells gradually worsened, and the epithelial swelling, congestion, fusion and layered curling, and proliferation of gill filaments became more severe. Moreover, with the increase of NaHCO 3 alkalinity stress, the abundance of Fusobacteriota, Cetobacterium and Mycoplasma first increased and then decreased, while the Proteobacteria, Actinobacteria, Dietzia and Citrobacter first decreased and then increased, and the Firmicutes and Candidatus Bacilloplasma continued to decrease, while Aeromonas continued to increase. Simultaneously, stress with NaHCO 3 alkalinity led to a decrease in gut microbiota diversity. In conclusion, 30 mmol/L NaHCO 3 alkalinity caused changes in enzyme activity, damage to the liver and gills, and alterations in the gut microbiota. In actual aquaculture production, close attention should be paid to the condition of fish after stress to prevent disease or damage to the body or organs.