Tolerance and serum metabolomics response of Yellow River carp (Cyprinus carpio haematoperus) to carbonate alkalinity

It is crucial for improving the utilization efficiency of saline-alkaline water to develop fish species suitable for aquaculture in such environments. Yellow River carp (Cyprinus carpio haematopterus) is an important aquaculture species in China. However, the lack of accurate assessment data on its alkalinity tolerance has hindered its promotion for aquaculture in moderately alkaline regions. This study investigated its tolerance to carbonate alkalinity (induced by NaHCO₃) and associated changes in serum metabolic profiles under long-term exposure to different alkalinity conditions. An acute stress test determined the 96-h median lethal concentration (LC₅₀) as 70.12 mmol/L and the safe concentration as 22.05 mmol/L, demonstrating strong alkalinity tolerance. Based on these results, fish were reared for 60 days in freshwater (control, A0) or alkaline water at concentrations of 10 (A10), 20 (A20), and 30 mmol/L (A30). Body weight gain in the A10 and A20 groups showed no significant difference compared to the A0 group, but was significantly higher than that in the A30 group (P<0.05), indicating minimally growth impact at low-to-medium alkalinity (≤20 mmol/L). Non-targeted metabolomic analysis of serum detected 1,069 metabolites across positive and negative ion modes. Compared to the A0 group, the A10, A20, and A30 groups were detected 301, 317, and 382 different metabolites, respectively. In the A10 and A20 groups, the different metabolites mainly involved pyruvate metabolism, starch and sucrose metabolism, while they mainly involved linoleic acid metabolism, biotin metabolism, taurine and hypotaurine metabolism, and butanoate metabolism in the A20 and A30 groups. These results suggested that carbohydrate metabolism pathways were primarily mobilized for energy demands under low alkalinity stress, while high alkalinity (30 mmol/L) triggered a shift towards lipid metabolism mobilization. Specifically in the A30 group, upregulated arachidonic acid and glutathione metabolism pathways indicated activation of mechanisms to counteract oxidative stress and inflammatory responses. This study provides valuable insights into the alkalinity tolerance of C. carpio haematoperus and the underlying serum metabolic adaptations, supporting its potential for cultivation in moderately alkaline waters.