Fish can be broadly divided into red and white fish, depending on the color of their muscles.
The muscles of red-fleshed fish such as tuna and bonito contain a large amount of a red pigment called myoglobin, while sea bream, mackerel, and sardines have little pigment and may appear white after heating.
Most white-fleshed fish generally live in coastal or deep-sea areas with relatively little exercise, while many red-fleshed fish are muscular fish that migrate in the open ocean.
White-fleshed fish is soft and pure white in color when heated, while red-fleshed fish has firm and firm muscle tissue after heating.
Although the flesh of salmon and some trout is pink, it is originally a white fish, a type of red pigment carotenoid, and not myoglobin.