Fishes are known to be good at extracting oxygen from water because oxygen has low solubility in water and they can survive in severe hypoxic medium. It indicates that the gas exchange organ of fish, known as the gill, is well-developed. In this study, a 1.67 kg of skipjack tuna due to having the high metabolic rate and fast swimming speed was selected to investigate fish gills in terms of heat transfer performance using the similarity between heat transfer and mass transfer. In doing so, the mass transfer coefficients on the water side and on the blood side of the skipjack tuna gill lamellae are calculated first. Then, hypothetical heat transfer coefficient is evaluated based on the similarity between heat and mass transfer phenomena. The result shows that the heat and mass transfer coefficient on the blood side is larger than the heat and mass transfer coefficient on the water side. That is, the overall transfer performance is dominated by water side performance. So that to calculate the overall heat transfer coefficient is sufficient to calculate the heat transfer coefficient on the water side. This research can be useful for the development of microfluidic devices related to heat and mass transfer.