Growth performance, biochemical indexes, and intestinal microbiota of Phoxinus lagowskii larvae under carbonate alkalinity stress

Abstract

The Amur minnow (Phoxinus lagowskii), a commercially significant cold-water fish, faces challenges in saline-alkaline aquaculture due to limited understanding of early-life stage adaptations. This study investigated the integrated adaptive mechanisms of the embryonic and larval stages in response to carbonate alkalinity stress (0–8 mmol/L carbonate alkalinity) through histological, physiological, and microbiome analyses. The results revealed that moderate alkalinity (2–6 mmol/L) did not compromise hatching success, larval survival, or growth performance. However, high alkalinity significantly reduced hatching rates, and induced hepatic oxidative stress characterized by elevated activities of SOD, CAT, ALT, and AST, and altered intestinal morphology. The gill osmoregulatory capacity was enhanced through upregulation of Na⁺/K⁺-ATPase (NKA) and Ca²⁺/Mg²⁺-ATPase (CMA) activities, along with increased expression of AQP1 and NHE3, highlighting critical ionoregulatory adjustments. Immune-related genes (TNF-α, IL-10, IL-13) in the liver were significantly upregulated. The intestinal microbiota exhibited resilience under alkalinity stress, with an increase in Proteobacteria and the probiotic Gemmobacter, alongside a reduction in the pathogenic Shewanella. This study elucidates the synergistic roles of hepatic antioxidant defense, gill osmoregulatory plasticity, and intestinal microbial dynamics in mediating alkalinity tolerance, providing actionable insights for optimizing saline-alkaline aquaculture practices.