In some regions, especially many Asian countries, fish is one of the most important sources of protein and nutrients available. Because of a high level of omega-3 fatty acids in many types of fish, consumption of fish helps to provide protection from some heart illnesses. Consuming a variety of fish and eating approximately one, 3.5 ounce serving or less of fatty varieties (such as tuna, salmon, and sardines) twice a week is thought to be a beneficial guideline to follow for good health and nutrition.
Today there is considerable concern regarding the over fishing of various species, leading to a significant decline in populations and potential for extinction. Another concern is the PCB and mercury levels of the water in which the fish live, thus raising the PCB and mercury levels found in the meat of the fish. Consequently, fish are beginning to be listed into groups of species that should be consumed and species that should be avoided. It is generally agreed that most farm-raised varieties of fish are safe to eat (farm raised salmon are an exception because they typically require significant amounts of mackerel, herring, and other fish as feed, however, if the source is dependable and uses environmentally sound practices, then farm raised salmon can be considered safe to consume). Varieties harvested in their natural habitat that are considered safe and in sufficient supply are halibut from the Pacific, salmon from Alaskan waters, sardines, striped bass, albacore tuna, big-eye tuna, or yellowfin tuna. The varieties harvested in their native habitat that are considered questionable are Chilean sea bass, Pacific cod, Atlantic flounder, grouper, monkfish, orange roughy, Atlantic and farm raised salmon, shark, snapper, sturgeon, and bluefin tuna. Species that are identified as those having the highest levels of mercury are fresh tuna, king mackerel, shark, swordfish, and tilefish.
If it is purchased fresh, make sure the fish has been displayed or stored on ice prior to buying it. Fresh fish will not smell fishy and should look moist, shiny, well-rounded and not dry or dull looking. After purchasing the fish, make sure it remains cold. It should be returned to refrigerated conditions as soon as possible after purchasing. For the best flavor and for safe consumption, fish should be used within 1 or 2 days of purchase. When storing fish, place it in the rear of the refrigerator on a bed of ice, securely wrapped in the paper from the fish market.
Fish can be prepared using almost any type of cooking method including baking, steaming, frying, grilling, broiling, or slow cooking. When cooking fish, care must be taken not to overcook the fillet, steak, or whole fish, which results in dry and somewhat tasteless meat. A general rule is to cook a fish 10 minutes for each inch of thickness. Realize that the fish continues to cook after removing it from the heat, so for a more flavorful result, begin checking for doneness prior to the 10 minutes per inch rule, allowing the fish to finish cooking as it sits prior to serving. Since the meat of the fish is somewhat translucent, it begins to become opaque as it cooks, which is another method of visually checking for doneness, especially for fillets that are most often not as thick as fish steaks. When fillets are opaque (white), it is an indicator of doneness. Some varieties of fish contain more fat, such as salmon or tuna, which can be cooked until opaque on the outside while remaining somewhat translucent on the inside. Another test to use for doneness is to check the meat with a knife to see if it is firm and beginning to separate or "flake". If the fish flakes too easily, it may be overcooked. The meat should slightly resist separating, but still be able to be separated, thus indicating it is moist and not too dry. When cooking fish that has not been boned, such as trout or pan fish, the meat should not drop off the bones, but instead should slightly resist removal.
The best procedure for checking doneness is to use a cooking thermometer, checking to make sure the fish has reached an internal temperature between 135ºF and 140ºF. To cook fish steaks that are slightly translucent in the center, remove the steaks from the heat when they reach an internal temperature of 120ºF to 130ºF. The fish steaks will continue cooking with the retained heat if they are covered and left to stand a few minutes prior to serving.