Protective role of nano-selenium on Gymnocypris przewalskii under saline–alkaline stress: a comprehensive analysis of transcriptomics and metabolomics

Tibetan naked carp (Gymnocypris przewalskii) is a unique freshwater fish adapted to high-altitude saline-alkaline water. Selenium nanoparticles (SeNPs) may enhance resilience in aquatic species by mitigating oxidative stress. This study used a combined transcriptomic and metabolomic analysis to explore the protective role of SeNPs in G. przewalskii under saline-alkaline stress. The transcriptomic analysis revealed significant alterations in the expression of genes involved in stress response, antioxidant defense, osmoregulation, and metabolism. KEGG pathway enrichment analysis of hepatic differentially expressed genes (DEGs) in juvenile G. przewalskii fed with SeNPs (NSE4_120) or basal diets (NSEC_120) under saline-alkaline stress revealed that the DEGs were significantly enriched in pathways such as "glycolysis/gluconeogenesis," and "thyroid hormone signaling pathway" (P < 0.05), suggesting that SeNPs may modulate these pathways for protection. Metabolomic analysis identified differentially abundant metabolites (DAMs) in the NSE4_120 versus NSEC_120 comparison group. Several differential metabolites associated with osmoregulation, including taurine, proline, and trehalose, were annotated to signaling pathways such as "metabolic pathways," "taurine and hypotaurine metabolism," "arginine and proline metabolism," and "starch and sucrose metabolism" pathways. These metabolites may play critical roles in the response of G. przewalskii to osmotic stress. In conclusion, our findings demonstrate that SeNPs play a vital role in enhancing the resilience of G. przewalskii against saline-alkaline stress through modulation of gene expression and metabolic processes, suggesting their protective effect against osmotic and oxidative stress. This study not only provides insight into the adaptive mechanisms of G. przewalskii under high saline-alkaline environmental conditions but also highlights the potential application of SeNPs in aquaculture strategies when fish are exposed to extreme environments. Future research should focus on elucidating the long-term effects of SeNP supplementation and exploring its mechanisms at the molecular level.