Fish with white flesh sit around, fish with red flesh zoom to town

Why do some fish have white flesh, such as flounder and tilapia, while others have red or orange flesh, like tuna and salmon?

The difference frequently has to do with a protein called myoglobin that stores oxygen for muscles and also acts as a pigment, said Keith G. Tidball, senior extension associate in the department of natural resources at Cornell University in Ithaca, N.Y.

Fish that have white flesh are generally those that are resting or mostly inactive throughout their lives, with intermittent short bursts of activity, Tidball said.

Other experts note that the fish get the energy for these bursts mostly by converting glycogen to lactate, rather than by using oxygen.

Red-fleshed fish are usually long-distance swimmers, and need high levels of oxygen for the sustained effort of their muscles, Tidball said. Myoglobin is what produces the predominantly red flesh in most tuna and other open-ocean fish, like mako sharks and swordfish.

Diet also can contribute to a red flesh color, he said.

Fish with orange flesh have generally been feeding heavily on ocean crustaceans including krill, which contain pigments called carotenoids, Tidball said.

He listed other dietary sources for color, like freshwater crustaceans and possibly terrestrial insects.

ActiveStyle on 12/15/2014

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