The large pelagic fishes and sharks, such as marlin, tuna have both white and
red muscle mass. In the tuna, the red muscle lies close to the vertebral
column, with the rest of the flesh having a pinkish color.
The large bluefins can reach an internal temp of 95degF (35deg C), and
generally swim constantly.
The red muscle tissue is slow-oxidative, the pink is fast-oxidative/glycolytic
and the white muscle is fast-glycolytic. In order listed, they proceed from
greater endurance/slower contraction to shorter endurance/faster contraction.
Many fresh water fish, more sedentary, have relatively little red muscle mass,
and are relatively ectothermic.
Chris McGowan has written a wonderful book that discusses this and other
fascinating information in _Diatoms to Dinosaurs, The Size and Scale of Living
Things_, Island Press, ISBN 1-55963-304-2. It's not a difficult read and I
think presents a lot of handy information.
M