One why of the warmth of warm-bodied fish

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Abstract
Tunas are unusual among fish in that they are warm bodied. One adaptive advantage to being warm is that warmth increases the rate of O2 delivery from the cell boundary to the mitochondria by myoglobin. Tuna have high rates of O2 uptake, much higher than other fish and close to the rates achieved by mammals. Tuna can maintain high cruising speeds for a long time. Tuna have much red muscle that contains a high concentration of myoglobin. The effect of temperature on simple diffusion of O2 was small but the potential affect on facilitated diffusion by myoglobin was large.