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We studied the effects of metabolic cold adaptation (MCA) in two populations of a eurythermal species, spotted seatrout (Cynoscion nebulosus) along the U.S. East Coast. Fish were captured from their natural environment and acclimated at control temperatures 15 degrees C or 20 degrees C. Their oxygen consumption rates, a proxy for metabolic rates, were measured using intermittent flow respirometry during acute temperature decrease or increase (2.5 degrees C per hour). Mass-specific standard metabolic rates (SMR) were higher in fish from the northern population across an ecologically relevant temperature gradient (5 degrees C to 30 degrees C). SMR were up to 37% higher in the northern population at 25 degrees C and maximum metabolic rates (MMR) were up to 20% higher at 20 degrees C. We found evidence of active metabolic compensation in the southern population from 5 degrees C to 15 degrees C (Q(10) < 2), but not in the northern population. Taken together, our results indicate differences in metabolic plasticity between the northern and southern populations of spotted seatrout and provide a mechanistic basis for predicting population-specific responses to climate change.