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According to the latest report of Intergovernmental Panel on Climate Change (IPCC),there will be increasing incidence of extreme temperature events worldwide due to the anthropogenically driven climate change.Most aquatic animals are ectothermic and their metabolism is highly temperature-dependent.This study aims to gain better understanding on the effects of temperature on the marine medaka fish Oryzias melastigma through measurement of oxygen consumption rate (OCR) and heat shock proteins (HSPs) expression.Thermal acclimation was conducted by increasing or decreasing temperature at the rate of 1°C/10 min and 2°C/day in a stepwise manner.The results showed that OCR was relative low from 26 to 30 °C and gradually increased and peaked around 24°C and 36-39°C.Their OCR reduced when the temperature was further increased or decreased.At the thermal extremes,the fish might have switched to anaerobic respiration for compensating the mismatched energy demand.Also,a significant up-regulation was recorded at 10,32 and 38°C for HSP 70 and at 38°C only for HSP 90.The over expression of these molecular chaperones represents a stress response to protecting the cellular structure and function at the thermal extremes.It is deduced that overall energy reserve will be depleted at such stressful conditions because the animal needs energy to synthesize functional proteins such as HSPs.More information will be given on the expression of HSP 20 and lactate dehydrogenase to further elucidate the thermal stress response of the fish.