In most instances, as soon as the translucent flesh turns opaque, the protein has adequately coagulated. Another test is to probe the thickest portion of the flesh with a fork. As soon as it flakes, the fish is properly cooked. Flaking occurs after heat has gelatinized the collagen in the myocommata, a type of connective tissue that holds the thin, parallel sheets of muscle fiber together. These separated sheets give the properly cooked fish flesh a flaky texture.
** Asian Recipes