Morphology, transcriptome and physiology analyses reveal adaptation mechanisms of Gymnocypris Przewalskii juveniles to saline-alkaline stresses.

Abstract

Background: Naked carp (Gymnocypris przewalskii), a fish endemic to Qinghai Lake, China, has attracted extensive attention for its adaptation to salinity and alkalinity stress. However, the survival mechanism of G. przewalskii against saline-alkaline water environments remains elusive. In this study, we aimed to reveal the causes of saline-alkaline tolerance of G. przewalskii through the analysis of morphological, physiological and transcriptomic dimensions. The combination of growth performance and physiological indexes, and the morphology of gill tissues and transcriptomics strengthened the connection between this experiment, and further explored and analyzed the causes of salinity tolerance of G. przewalskii.

Results: Analysis of growth indices revealed weight gain rate (WGR), specific growth rate (SGR), average daily gain (ADG), and specific growth rate of length (SGRL) were promoted under mild alkaline stress and saline-alkaline stress. The alkalinity of A24.36 (7.80 mmol/L) and a saline-alkalinity of SA23.05 (3.84‰, 7.38 mmol/L) is most favorable for growth. All stresses caused shortened length of gill lamellae and between-lamellae distance. At the same time, stress led to a substantial increase in glycogen content and enhanced fructose-1,6-bisphosphate aldolase (FBA) activity in the liver and muscle. The transcriptome results in gills showed significant enrichment of biological processes such as manganese ion transport in alkaline stress, and reflection of stimuli, immunity, etc. in saline-alkaline stress. In gills, energy metabolism process, PI3K signaling pathway were significantly activated in both alkaline stress and saline-alkaline stress, NF-kappa B signaling pathway was significantly activated downstream of PI3K in alkaline stress; mTOR signaling pathway, MAPK signaling pathway and Rap1 signaling pathway were significantly activated downstream of PI3K under saline-alkaline stress.

Conclusion: This study unveiled the changes in growth indices, gill morphology, physiological parameters, and transcriptomics, which facilitated elucidation of the adaption mechanism of G. przewalskii juveniles to alkaline stress and saline-alkaline stress.