Which meat do you prefer? White or dark? Yes, this is still "Fish Talk", but; as it happens, both fish and birds have both white and dark meat; or, more specifically, white and red muscles. Why? Well, because the two different types of muscles perform different jobs. Red or dark muscles are used to perform routine, sustained, "cruising speed" type of activities; white muscles take over when a short-term, powerful burst of activity is needed. (Note that the "white muscle" of salmon and trout is actually red - but because of a pigment - not because of a different function. The "red muscle" of trout and salmon is that dark, brownish flat strip of muscle that is just under the skin along the lateral line.)

Let's start at the beginning. What does a muscle need to do its job? An energy source and oxygen. How does a muscle get energy and oxygen? From the blood. Think about that for a moment; and then consider... why is red muscle red? Because it has an abundant, rich supply of blood vessels which transport a load of nutrients and oxygen for energy and which carry away metabolic wastes (called lactic acid) after the energy is produced. This is just what is needed to support the sustained, routine muscular activities.

Okay, so what about the white muscles; don't they have the same metabolic needs? Well, yes, but on a different scale, because they are actually quite different. First, they are used for short periods of powerful bursts of exertion in those "fight or fright" situations. (Usually, for fish - or birds - this means to escape or flee from a predator; or, to pounce on some prey.) The white muscle mass is usually large for short, powerful actions and the red muscle is the overdrive for "cruising" activities. So, white muscle does not have a good blood supply; therefore, it lacks an oxygen supply that is needed for a sustained effort and, this also means that it lacks a good system of fast removal of metabolic lactic acid. The bottom line... the white muscle is big and powerful; but without a substantial blood supply, the power cannot be sustained.

Why not just make all muscles red? Good question.... but actually, the answer is quite simple. If the entire muscle mass had a good blood supply, not only would there be more blood, but also, the heart would have to be much bigger and stronger to keep all that blood moving all the time even though only a small portion of the muscle mass would usually be needed. In addition, the animal would need to eat much more food and the heart would need to work much harder to constantly maintain such a muscle mass when only a small portion would be used routinely.

So what does this all really mean to the fish.... and, how does this affect you and me? Well, if a fish is chased by a predator or when a fish is hooked, the "fright mechanism" kicks in and the white muscles take over. The first burst of energy is usually the strongest. But with each burst, each struggle, the oxygen in the white muscles becomes more depleted. The energy supply becomes exhausted, the lactic acid accumulates, and the fish tires. This is why we are advised to land a fish quickly so it can be released before the depletion is severe and recovery can be faster.