12.1 Round fish and flat fish

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What fish flesh is like

A fish is an animal with a backbone that lives in water, swims with fins and breathes through gills. More than 30,000 species are known. Most of them live in the sea; far fewer live in fresh water.

Fish muscle is built from short fibers held together by thin, delicate sheets of connective tissue. That is why fish is tender before it is cooked. Cooking fish is not about making it tender. Its jobs are to firm up the protein and bring out the flavor.

Fish flesh is pale because it lacks myoglobin, the protein that carries oxygen in red meat. Salmon and some trout are orange only because of pigments in their diet.

Fish carry far less fat between their muscles than meat does, but the fat they have changes how they cook. Cooks sort fish into two kinds:

• Fatty or oily fish, such as salmon and mackerel, hold a fairly large amount of fat.
• Lean fish, such as cod and haddock, hold very little. Shellfish are lean as well.

Keep this split in mind: it helps decide how each fish is best cooked.

Two body shapes

Fish are grouped by the shape of the body and the bones.

• Round fish swim upright, with one eye on each side of the head. The body can be round, oval or squeezed flat from side to side.
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• Flat fish swim lying on one side, and both eyes sit on the upper side of the head. They live on the sea floor, most of them in deep water. The upper skin is dark, and can change color to hide the fish from hunters. The scales are small, and the fins on the back and underside run the whole length of the body.
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Names that mislead

Telling one fish from another is hard, for several reasons:

• Many species in a family look alike.
• One fish may have several local names.
• One name may mean different fish in different places.
• A fish with an unappealing name is sometimes sold under a nicer one, or under the name of a more popular fish.
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• Menus also use foreign names.

In the United States, the FDA (Food and Drug Administration) publishes a list of accepted market names for fish, called The Seafood List. Sellers are strongly urged to follow it, but the rule is hard to enforce.

Salmon

Salmon live in the northern Atlantic and Pacific Oceans and swim back up the rivers where they hatched to spawn. The pink-red color of the flesh comes from carotenoids, fat-soluble pigments in the crustaceans salmon feed on. Cooked salmon breaks into large flakes.

• Atlantic salmon is the most important salmon in trade: about a quarter of all salmon produced. Nearly all of it is farmed, in Norway, Canada and Scotland; wild Atlantic salmon is almost never for sale. The flesh is rich pink and moist, and the fish average 4 to 12 lb (1.8 to 5.4 kg). The place it comes from is often part of the name, as in Scottish Atlantic salmon.
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• Chinook or king salmon come from the Pacific. They average 5 to 30 lb (2.2 to 13.2 kg). The flesh is red-orange, fatty and rich in flavor. They are often named for the river they come from, and the inside of the mouth is black.
• Coho or silver salmon have pinkish flesh. Wild coho weigh 3 to 12 lb (1.3 to 5.4 kg); farmed coho are much smaller, usually under 1 lb (450 g).
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• Chum, sockeye, red, blueback and pink salmon mostly go into cans, though some are sold fresh or frozen.

Salmon can be broiled, grilled, poached, steamed or baked. Frying is not advised, because the fish is already so fatty. Salmon is also cured. Gravlax is salmon packed in salt, sugar and dill for one to three days. Lox is cured in a salted brine and then, usually, cold-smoked. In the eastern United States, Nova means a cold-smoked salmon that is less salty.

Trout belong to the salmon family. Most trout for sale are farmed rainbow trout. Their fat is low to moderate, their texture flaky, and their flavor so delicate that a strong sauce can bury it. At 8 to 10 oz (225 to 280 g), one trout makes one portion. Bake, pan-fry, smoke or steam it. Lake trout, also called char, are too fatty to have much value in trade.

Cod

The cod family takes in Atlantic and Pacific cod, pollock, haddock, whiting and hake. Cod is lean, white and firm, with a mild flavor, and it flakes apart easily. Most methods suit it. Grilling does not, because the flakes fall apart on the grate.

• Atlantic cod sells better than any other fish in America. It comes fresh (whole, drawn, or as fillets and steaks), frozen (often as breaded sticks or portions), smoked, and dried and salted. Cod can reach 200 pounds (90 kilograms), but most at market weigh 10 lb (4.4 kg) or less. Scrod is a trade name for cod or haddock under 2 lb (1.1 kg) or under 20 inches (50 cm) long.
• Haddock look like small, slim Atlantic cod, at about 2 to 5 lb (900 g to 2.3 kg). The taste is stronger and the texture softer than Atlantic cod.
• Pacific cod, or gray cod, is less plentiful and is usually sold frozen. It should be labeled "true cod" so no one confuses it with rock cod or black cod, which are not related.
• Pollock is plentiful in the northern Atlantic and Pacific. Its raw flesh is gray-pink and turns white when cooked. Much of it is frozen at sea and later made into surimi; it is also salted or smoked.

Tuna

Tuna include bluefin, yellowfin, bonito, bigeye and blackfin. Ahi is a market name for yellowfin or bigeye. All are part of the mackerel family, all live in warm seas, and a single fish can weigh several hundred pounds. Bluefin is the finest for sashimi, and overfishing has made it scarce. Canned light tuna is usually yellowfin or skipjack; canned white tuna is albacore, also called longfin. Pacific tuna frozen at sea is called clipper fish.

Tuna reaches market as four boneless loins. These are cut down into steaks, cubes or chunks. Raw tuna is deep red, with low to moderate fat; fattier flesh is preferred for sashimi. A strip of dark, red-brown, very fatty muscle runs along the side of the fish, and it can be cut away. Cooked tuna turns light gray, firm and mild. It grills and broils well, with a marinade or a brushing of seasoned oil. Cooks often serve it medium rare so it does not dry out.

Other round fish

Flesh, market sizes and good methods for other round fish. A dash means no figure is given.

A few warnings travel with these fish:

• Mako shark is sometimes passed off as swordfish.
• A shark that smells of ammonia was badly handled when it was caught; do not buy it or eat it.
• Red-skinned rockfish are often wrongly sold as red snapper, so snapper fillets keep their skin on to show what they are.
• Tilapia is sometimes sold as cherry or sunshine snapper, though it is no snapper at all.

Flat fish

Flounder is lean and firm, pearly or pinkish white, sweet and mild. Most have the head and guts removed on the boat, and reach market as fillets, fresh or frozen. These fillets are very thin. They dry out and spoil easily, so handle and store them with care. Cook them in ways that keep moisture in: poaching, steaming and frying.

Sole is a name with a good reputation, so it is put on many fish that are not true sole. The FDA allows many flat fish to be sold as sole in the United States, yet no true sole is caught in American waters: any American "sole" is a flounder.

• English sole are flounder from the American West Coast, often sold simply as fillet of sole. Plentiful, fair to average in quality.
• Petrale sole, another West Coast flounder, is thought the best of the American soles. Its fillets are thicker and firmer than most.
• Domestic Dover sole, a Pacific flounder, is less delicate and less tasty than the others. A parasite often leaves its flesh slimy and jelly-like, so choose another sole or flounder when you can.
• Lemon sole, also called black back or winter flounder, is the most plentiful and popular flounder on the East Coast. It averages 2 pounds (900 grams).
• True Dover sole belongs to the family Soleidae and comes only from the waters off England, Europe and Africa. It is lean, pearly white and delicate, yet it stands up to many sauces and seasonings. It is a classic of fine cooking, imported whole or as fillets.

Halibut are among the biggest flat fish, often up to 300 pounds. Only two species are recognized in the United States: Atlantic and Pacific halibut. Both are lean, firm and snow white, and sweet and mild in flavor. California halibut is really a flounder and averages 12 pounds (5.4 kilograms). Halibut is cut into boneless steaks or cubes for skewers. It dries out easily. Poach, bake, grill or broil it, and serve it with a sauce.

Turbot caught in the Pacific is an ordinary fish. The European turbot is another matter: a large, diamond-shaped flat fish, valued for its firm white flesh and delicate flavor, and also sold as brill.