The other day I was going through an old email folder I keep titled "Food & Wine." It's where I put interesting emails, links, recipes, and other electronic ephemera I have collected over the years. Scrolling down through the years, I found an old email about fish, dated April 16, 2008. After over five year's time, I have no clue where this email came from—whether I found the information on the Internet and emailed it to myself or whether someone sent it to me. I had totally forgotten why I saved it, but after reading it, I recall why.
It was information about fish and how and why different types of fish have different flavors and why some fish are better prepared by frying, broiling, baking, or poaching. I thought it would be fun to share this information.
Not surprisingly, the factors that determine a fish's flavor are numerous. Obviously, where the fish came from is the biggest factor: salt water vs. fresh water or cold water vs. warm water. Other factors, however, are less obvious. For example, fat content. Fatty or oily fish may have more flavor, but they also spoil faster, which is why tuna must be well iced. And like their landlocked counterparts, a fish's activity level affects flavor. The turkey is a good example.
The turkey's active muscles, such as the legs and thighs, used for running away from Pilgrims with the funny guns and goofy hats, are full of blood vessels. These blood vessels contain myoglobin (or muscle hemoglobin), which delivers oxygen to the muscles. You guessed it! The more myoglobin the muscles contain, the darker the muscle. (In my opinion, the dark meat of turkey and chicken also contains more flavor.)
These kind of muscles are referred to as "slow-twitch." Slow-twitch muscles are built for endurance, thus allowing the muscles to work for long periods of time. As a result, the turkey can run around all day without getting tired, just as the tuna can swim all day without getting tired.
White meat, however, is the result of well-rested muscles. These muscles are used for flying, which a turkey rarely does, and when it does, it is for short distances. As you might expect, there is less of a need for an oxygen-rich blood supply for these muscles. These kinds of muscles are referred to as "fast-twitch"—designed for quick bursts of energy. Think of a flounder lounging on the sea floor, who only occasionally has to make a quick escape.
Therefore, the more active the fish, as well as the distances it travels (e.g., tuna, salmon, and swordfish), the more slow-twitch, red muscle fibers and fat the fish will have. This makes it a good candidate for more "robust" cooking, such as grilling. The less active the fish (sole, flounder, and catfish), the more "delicate" the cooking technique (e.g., poaching or roasting).
Who knew that a little knowledge about ichthyology could make one a better cook?!