Comparative study of fish adaptation at cellular and genetic levels across eco-sensitive zones with contrasting oxygen and temperature regimes

Unravelling the physiological adaptations that enable fish to thrive under diverse environmental stressors is crucial for predicting their resilience to climate change. However, linking molecular mechanisms to ecological contexts remains a significant challenge and such studies are greatly lacking. To close this data gap, we conducted a physiological and molecular mechanisms-integrated comparative study of representative fish species from two ecologically contrasting regions: the Indian Sundarban mangrove estuary and the Sub-Himalayan Terai-Dooars hill streams. We assessed erythropoietic activity, cell cycle dynamics, reactive oxygen species levels, and the expression of genes integral to hypoxia response, electron transport chain regulation, adaptive remodeling, and stress modulation. Our results demonstrate that fish inhabiting the Terai-Dooars region exhibit substantially higher erythropoietic efficiency, elevated reactive oxygen species levels, and significant upregulation of hypoxia-inducible and adaptive remodeling genes as compared to their Indian Sundarban counterparts. These findings suggest that the challenging environmental conditions of the Terai-Dooars-characterized by low temperatures, high water velocities, and physiological hypoxic stress-drive distinctive physiological and genetic adaptations in fish populations. Analysis of variance (ANOVA) on Principal Components (PCs) revealed species-specific cellular variability modulated by regional environmental pressures, emphasizing the interaction of intrinsic and extrinsic factors in shaping adaptive responses. This study bridges critical knowledge gaps by linking physiological traits to ecological contexts, providing insights into community-level adaptation mechanisms. The findings highlight convergent evolutionary strategies and propose molecular and cellular biomarkers for assessing resilience under future climate scenarios. Finally, these ecophysiological insights will enhance the comprehensive understanding of species responses to environmental heterogeneity, with implications for conservation and ecosystem management in the face of global environmental change.