Assessing the thermal limits and metabolic profiles of small indigenous fish species: Informing conservation and aquaculture in a changing climate

This study explored the thermal tolerance and routine metabolic rate of ten small indigenous fish species from Northeast India: Amblypharyngodon mola , Esomus danrica , Puntius sophore , Gudusia chapra , Heteropneustes fossilis , Botia dario , Lepidocephalichthys guntea , Mystus cavasius , Aplocheilus panchax , and Glossogobius giuris . Fish were acclimated to 20°C, 25°C, and 30°C for two weeks prior to experiments and assessed for critical thermal maxima (CTmax), critical thermal minima (CTmin), lethal thermal maxima (LTmax), oxygen consumption rates, and respiratory quotients using standardized methods. The results revealed significant interspecific variations: CTmax ranged from 36.4°C to 41.7°C, CTmin from 8.7°C to 15.2°C, and LTmax from 41.5°C to 44.9°C. Oxygen consumption rates varied between 0.26 and 1.07 mg O₂/g/h, with respiratory quotients ranging from 0.76 to 1.01. Heteropneustes fossilis (CTmax: 41.7°C at 30°C acclimation) exhibited the highest thermal tolerance, while Amblypharyngodon mola had the lowest (CTmax: 38.2°C at 30°C acclimation). Differences in thermal tolerance between species were statistically significant (p<0.05). Notably, CTmax was positively correlated with oxygen consumption rates, suggesting a connection between metabolic rate and heat tolerance. These findings enhance our understanding of the physiological adaptations of these species to their thermal environments and underscore their conservation needs amidst climate change. • Critical thermal maxima (CTmax) ranged from 36.4°C to 41.7°C across ten small indigenous fish species. • Heteropneustes fossilis demonstrated the highest thermal tolerance and acclimation capacity. • Routine metabolic rate positively correlated with thermal tolerance (r = 0.91, p<0.001). • Species showed differential vulnerability to climate change, with Amblypharyngodon mola potentially at higher risk.