Have you ever wondered why fish has such a different texture than other animal foods like beef, chicken, game, or poultry? It is much more delicate and soft, and although some fish flesh is firmer than others, it flakes when cooked. What makes fish “meat” so much different?
A very good answer was provided to this question recently on Quora. The answer is in how fish have their muscle fibers arranged. Whereas our muscles and the muscles of other terrestrial vertebrates are arranged in long bundles, fish muscles are short, typically less than one inch, and are arranged in sheets called myotomes. These myotomes are separated from each other by collagenous sheaths of connective tissue called myocommata. This arrangement causes fish flesh to flake.
Moreover, fish muscle has much lower amounts of collagen than the muscles of land animals. Collagen is a major component of skeletal muscle, making up much of the connective tissue between and around muscle fibers. The amount of collagen in meat determines, in large part, its texture. Meat with more collagen will be less tender than meat with less collagen. Different bovine muscle groups contain more or less connective tissue, and thus collagen, depending on how often they are used. More heavily used muscles have more connective tissue and are thus less tender (although they may quite flavorful) than muscles that are used less. However, while land animals average about 15% collagen, fish only averages around 3%. This collagen breaks down more easily and turns to a gelatin-like substance, making for a much softer texture when eaten.
All of this results in a soft, delicate, flaky texture. You can clearly see the myotome structure of fish muscle in the fillet of iridescent shark pictured below.
Fish Texture: Delicate, Medium Firm, and Firm
Given that all fish flesh is more delicate than that of land animals when cooked, some fish are more delicate than others. Fish can be loosely grouped by firmness (delicate, medium-firm, and firm). The table below lists different fish by texture, arranged in order of flavor, with mild flavored fish at the beginning moving to fuller flavored fish as the end. For example, cod and whitefish are both delicately textured fish, but whitefish as a stronger flavor than cod, so appears further down the list. Shellfish are not included in this list.
|Fluke (Summer Flounder)||Delicate|
|Sea Trout (weakfish)||Medium-firm|
Why is Fish Different Colors?
You may also be wondering why some fish is almost pure white while others are darker colored or red. The pigmentation of fish flesh depends on the amount of oxygen carrying myoglobin in the muscle. The amount of myglobin, in turn, depends in whether the fish has muscle which are predominantly “fast-twitch” muscles, “slow-twitch muscles, or a mixture of both. Fish with mostly fast-twitch muscles are white-fleshed fish. These fish rely on quick and explosive bursts of activity followed by long periods of very low energy activity. Fish with mostly slow-twitch fibers need to swim very long distances, so require more oxygen in their muscles. These fish are the endurance athletes of the fish world. Some fish have some of both, so that they will have meat of varying shades of white or dark. Whereas sole will be very light-colored, tuna can be a very deep red, but with varying tons of lighter and darker flesh. The fat content of fish also affects how dark the flesh appears. Some fish, as well, may have other pigments, which affect the color, such as salmon and sea trout, which have a carotenoid pigment called astaxanthin, giving them an orange-pink color. This cartenoid is similar to beta-carotene, which gives carrots their orange color. This pigment accumulates in the fat cells in the muscle of the fish. They get this pigment from the insects and crustaceans they eat, which in turn get it from plankton.
You will notice a similar color when you cook shrimp, lobsters, crayfish, or crabs. These all contain astaxanthin, but it is bound to a protein in their shells, causing the color to be reddish brown or even bluish-green, rather than deep red. When cooked, the protein is denatared, so that the true color of the astaxanthin comes out. Similary, when salmon or sea trout digest this protein, it is denatured, and the red pigment is stored in the fat deposits over time. Many commercially farmed salmon are provided astaxanthin artificially, using synthetically or naturally derived products so that farmed salmon have the expected characteristic color.