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Changing climate of Sundarban estuaries (UNESCO World Heritage) is a threat to the stasis and distribution of its most fish species.Little is known of the eco-physiology of fishof the Sundarban estuaries so predictions on their stasis andfuture distributionin altered climate hardly exists.This article is a pioneering attempt towards that by looking at the eco-physiology of theMystus gulio. Catfish Mystus gulio is widely distributed in the estuaries of Sundarban and in South-East Asia. Length Specific Oxygen Consumption (LOC) of Mystus gulio (sub-adults 3.8 to 5.5cm) was evaluated in salinity 5 PSU, 10 PSU, 15 PSU, and 20 PSU at 20 degrees C, 24 degrees C, 28 degrees C, and 32 degrees C for an assessment of the combined stress arising from salinity and temperature variability. Hypothesis was, LOC would increase with the steeper gradients of salinity-temperature combinations but it would decease beyond the optimal thermal range of M. gulio. LOC varied significantly between different salinity-temperature combinations and was significantly less at high-salinity-high-temperature. Variability of the amplitudes of the salinity (reported previously that it could be up to 25%) and temperature gradients of the estuaries in Ganges delta has increased in recent decades so high-salinity-high-temperature scenarios cannot be ruled out. We suggest that in such scenario early life stages of fish like Mystus gulio may reduce their movement behaviour and increase the tendency to hide at the bottom of oligohaline sections of an estuaryto avoid deathfrom respiratory stress.