How to Cook Fish (part 1)

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   Source the freshest fish available. Of course, fresh ingredients is important anytime you're cooking, but with fish, it's especially important. You can disguise some three-day old chicken pretty easily, but it's much tougher to disguise some cod that's been sitting around for three days. In order to cook the best fish of your live, you'll want to get cozy with your fishmonger.
   

   • The best trick to getting the freshest fish available is to simply ask. Go up to the fishmonger manning the fish in your local grocery store and ask him what's fresh today. This will sometimes require being flexible about the kind of fish you cook, but it's for the better. Fresh fish almost invariably tastes better than old fish, whether it's salmon, mackerel, tuna, or swordfish — the list goes on.
   • The freshest fish will smell of the sea (briny) but not fishy; the gills should be bright and moist; the meat firm and springy; and the scales should not be dull or flake off easily.
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   Get familiar with your thermometer. The secret to cooking fish is knowing the temperature at which they're finished cooking. In order to do this, you'll want to use a food thermometer until you get the hang of things and can tell whether your fish is done by touching or merely looking at it. Most fish are perfectly cooked when they reach an internal temperature of 120° - 145°F (~49° - 63°C).^[1][2]
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   Know that it's okay to undercook most fish. Ever heard of sushi? Or how aboutceviche? These are two fish dishes that are not cooked at all. Unlike undercooked poultry, which carries the risk of salmonella, fish are okay to eat undercooked or even raw.^[3]
   

   • Although raw or undercooked fish can contain parasites, the incidence rate of serious health concerns is serially overstated.^[4] You should feel very safe eating undercooked fish.
   • Some fish are better raw (or undercooked)! Fish like tuna are often given a lightsear on both sides before removing from the heat and serving. Tuna tartar, famously, isn't cooked at all.
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   Know the three basic kinds of fish. Fish come in three basic varieties, each of which tends to be cooked in a different way and contains different nutritional properties. Knowing your way around the basic varieties will help you become a better cook:
   

   • White fish — cod, plaice, sole, and haddock, among others. These fish have translucent skin that turns an opalescent white when being cooked. Usually battered and deep fried, they form the basis of the classic English fish and chips.
   • Oily fish — salmon, trout, and sardines, among others. Oily fish are oilier than other varieties, but contain good oils (omega 3 fatty acids). They are often grilled, baked, or steamed.
   • Shellfish — shrimp, scallops, mussels, and oysters, among others. Shellfish are categorized either as "crustaceans" (shrimp) or "mollusks" (oysters). Commonly bottom feeders, shellfish are harder to digest than either white or oily fish.
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   Experiment with marinades, but know that most fish taste wonderful with just salt and pepper. There are tons of different marinades that you can experiment with when cooking fish — soy sauce and honey works great on salmon, while olive oil and lemon work nice on whitefish. But ultimately, great fish — like great meat — tastes exquisite when you let the taste of the actual fish, and not the marinade, take over.
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   Cook with your fish as dry as possible. Dry off your fish before cooking, whatever method of cooking you decide to use. Especially important for frying or pan-frying, excess moisture will cool down hot oil. Try to pat down fish fillets or steaks with a dry paper towel before cooking for best results.
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   Thaw your fish before cooking. For best results, of course, you'll want to use fresh fish. But let's face it — fresh fish is expensive, a luxury that not all of us can afford. Frozen fish is a nice alternative, but you'll want to thaw your fish for a day in the refrigerator before cooking for best results. Oh, and remember to pat it down to remove excess moisture before cooking!
   

   • You can bake frozen fish, for example, but you'll want to double the normal cooking time from your recipe. Cooking frozen fish is very tricky however, and shouldn't be done as a rule of thumb if you can afford it.