Cookbook:Fish

Fish
Fish
Category	Seafood

Fish, or fin fish to distinguish from shellfish, are bony, non-mammalian sea creatures.^[1] They come in many different varieties.

Characteristics

Name

One characteristic of fish uncommon to other food animals is the sheet variety of names given to them.^[2] In many cases, the same fish can have lots of different names even in the same language.^[3] In some cases, this occurs for commercial or marketing reasons.^[4]

Structure

Typically, the basic structure of fin fish is conserved. Many, if not most, fish have fins and tails.^[4] They have a central backbone and ribcage,^[4]^[2] with slabs of muscle on either side of these, and sometimes tiny pinbones throughout the flesh.^[2] Fish bones are much softer than those of terrestrial animals like cows or chickens, though they are still unpleasant to eat. Freshwater fish tend to have many smaller bones, while saltwater fish tend to have fewer, thicker bones.^[2]

Shape

Fish are usually divided into two main classes: roundfish and flatfish.^[1] Roundfish are tubular in shape, swim vertically, and have one eye on either side of the head.^[4]^[2] On the other hand, flatfish are pancake-like with flat, oval bodies.^[1]^[4]^[2] They have dark skin on the side facing up and light skin on the bottom.^[2]^[5] They swim horizontally, and both eyes are on the top side of their bodies.^[1]^[4]

Fat

The fat content of fish ranges from 0.5–20% across all species.^[1]^[2] Compared to land animals, fish have much less intermuscular fat,^[4] and lot of it is located under the skin and around the belly area.^[2] Lean fish are relatively low in fat, while fat fish have higher amounts on average.^[1]^[4] In addition, fat fish are typically more intense in flavor than lean fish.^[2]

Color

The color of fish flesh depends largely on the animal's lifestyle, including environment and diet. The majority of fish have white/light flesh low in myoglobin, as they are supported by the surrounding water and don't need endurance muscle.^[2] Their dark flesh, if present, is typically limited to a thin layer just under the skin and sometimes along their center line.^[2]^[6] On the other hand, active long-distance fish like tuna have significantly more red flesh.^[2]^[6] The distinct pink color of salmon flesh comes from the pigmented crustaceans in their diet. All fish flesh starts out translucent when raw and becomes opaque with exposure to heat or acid.^[2]

Flavor

Fish flavor depends on species, muscle type, salinity, fat content, and diet.^[2] Freshwater fish have a milder flavor because they accumulate fewer amine-containing compounds in their flesh,^[2] and they aren't exposed to bromophenols, which provide a distinctive "oceanic" character.^[6] High-myoglobin fish like tuna may have a flavor tinged with iron. High-fat fish carry more flavor in their flesh than do lean fish.

Texture

Fish muscle fibers are folded over on themselves and separated by connective tissue, which gives the flesh a flaky texture when cooked.^[2] Compared to that of land animals, fish flesh is very delicate in texture, largely due to its weaker and less prevalent connective tissue.^[1] Fish muscle fibers are shorter,^[2] and their collagen turns to gelatin and dissolves around 46–55°C (115–131°F).^[2] As a result, fish is easy to overcook and toughen^[1]—as the flesh is heated, the gelatin renders out, the muscle fibers coagulate, and ultimately moisture is squeezed out of the flesh, making it dry. Because the collagen (by way of gelatin) provides a sensation of moistness, the tail area, which is rich in collagen, feels more succulent.^[2] By the same principle, fish lower in collagen feel drier overall.^[2] Certain fish have life cycle stages that negatively impact the quality of the flesh, which becomes spongy and unappetizing in texture.^[2] Fish bones are soft and become softer when cooked near boiling temperature.^[2]

Fish steaks

Cuts

Fish fillet

Fish doesn't have the same diversity of cuts as, say, beef. However, it is classified differently based on the degree to which it has been broken down. The following terms describe fish in different processing stages:

Whole: completely intact fish just as it was slaughtered^[1]^[4]
Drawn: guts removed^[1]^[4]
Dressed: drawn with scales, fins, tail, and sometimes head removed^[1]^[4]
Steak: cross-sectional slice of the fish, often containing a piece of spine^[1]^[4]^[5]
Fillet: only the meaty side of the fish, either with skin or without^[1]^[4]^[5]
Butterflied: fillets still joined together, usually at the back, and opened flat like a book^[1]^[4]
Sticks: simple vertically sliced skinless fillet^[1]
Tranches: fillet diagonally sliced to give pieces with large surface area^[1]^[4]

Selection and storage

The first step to fish selection is to understand responsible and sustainable fishery. Many species of fish worldwide are over-fished or poorly managed, which can have negative environmental impacts.^[4] Check a reputable source such as the Monterey Bay Aquarium's Seafood Watch service to make sure you are choosing fish from a well-managed fishery.^[1] Your fishmonger should also be able to tell you detailed information about the fish, including where it is sourced from, how it was caught, how it has been processed/stored, and when it was delivered, if applicable.^[5] When available, try replacing unsustainable fish with similar but more sustainable varieties.^[4]

When purchasing fish from a vendor, there are several factors to assess in order to make sure you are getting good quality fish. Starting at the surface, the skin and fins should be moist, shiny, and clean, with no bruising, discoloration, or stickiness.^[1]^[4]^[2]^[5] If present, the scales should be intact.^[5] Any slime, if applicable to a given species, should be clear and not cloudy.^[1]^[5] The gills should also be moist and bright red/pink in color, not a duller rusty or brown color.^[1]^[4]^[2]^[5] The eyes should be rounded and shiny, not sunken and dull.^[1]^[4]^[2]^[5] If the fish is whole, there should be neither bloating or discoloration near the belly.^[5] If gutted, make sure there is no indication of belly burn.^[1]^[5] If the vendor lets you touch the fish, the flesh should feel firm and spring back after you remove your hand.^[1]^[4]^[2]^[5] There should be no spongy texture or flaking of the flesh, and a knife should cut not pull through the flesh.^[5] If they let you smell the fish, it should not smell of ammonia, sulfur, or other spoilage—the stereotypical strong "fishy" odor actually indicates bacterial or enzymatic breakdown of compounds in the fish.^[1]^[4]^[2] At most, it should smell of the sea in the case of ocean fish.^[2] Ideally, the fish should be stored on ice and should not be touching any other fish in the case.

Fish is extremely perishable,^[1]^[5] with cold-water and high-fat species spoiling even faster than warm-water and lean species.^[1]^[2] Fish should be gutted as soon as possible after slaughter to prevent degradation of the flesh.^[1] Under perfect refrigeration conditions and with optimal processing, fish will last up to 10–12 days after slaughter.^[5] Subpar conditions shorten this shelf life, and in many cases purchased fish is only good for a handful of days under refrigeration.^[1] The optimal way to store fish is on flaked or crushed ice in the refrigerator^[1]^[7]^[8]—this keeps them as close to freezing as possible. Whole roundfish should be packed in ice in the "swimming position",^[5] which is to say with the backbone facing the sky. Flatfish should be packed at an angle with their dark side facing down.^[5] Fillets and other smaller cuts should be wrapped in plastic when packed in ice.^[1] Ideally, the icing should be done in a perforated tray to allow the melted ice to drain away from the fish and prevent pooling next to the flesh. The next-best way to refrigerate fish is in a refrigerator set to 0°C/32°F.^[1]^[4]^[7] A 40°F fridge is least preferable.^[4]

Modern freezing technology has made freezing fish a very viable option for extended shelf life without much loss in texture or flavor.^[5] The best way to freeze fish is with a cryogenic substance such as liquid nitrogen—this quickly freezes the fish, forming very small ice crystals, which avoids damaging the texture.^[5]^[8] Blast chilling is also a good option.^[5] To freeze fish at home, cut it into portions no thicker than 2 inches (5 cm), seal it in a plastic bag with no air (vacuum is ideal), and submerge it in several inches of cold water before placing in a standard freezer—this significantly reduces the risk of oxidation and ensures a slow thawing.^[5] Store frozen fish below 0°F (–18°C),^[4] and thaw it in the fridge to reduce the risk of ice crystals puncturing the adjacent flesh and damaging the texture.^[1]^[2]^[5] Thawing under cold running water is also an option if necessary.^[1]^[5] Note that fish that are particularly susceptible to oxidation like tuna should be stored well below the freezer temperature for other fish.^[2]

Canned fish is often good, but very different in taste, and selection is limited. Canned salmon and anchovies are particularly high in calcium, because the bones are softened by canning and are eaten with the flesh.

Preparation

Gutting

It is important to remove the guts as soon as possible after the death of the fish. To do so, make a cut down the belly from the anal opening to the gills—be careful not to puncture the internal organs when doing so. Cut out the guts by the tail and right behind the head, remove them from the abdominal cavity. Use a spoon to detach and remove the large vein in the cavity, as well as any residual guts. Finish by rinsing out the abdominal cavity.^[5]

Scaling

To scale the fish, you may use either a specialized scaling tool or the dull back of a chef's knife.^[4]^[5] Hold the fish in a perforated pan to collect the scales, and run the tool against the scales from the tail to the head. Don't push too hard, as this can bruise the fish. Rinse well when finished to remove any sticking scales.

Filleting

Round fish typically make 2 fillets, and flatfish can yield 2–4 depending on the size.^[1]^[5] Flatfish should have their light side removed first to prevent crushing.^[5]

Skinning

To skin a fish fillet, place it skin-side down on your work surface. Start at the tail, and place the place at the interface between the flesh and the skin. Angling the blade down towards the skin, grip the skin, and use a smooth sawing motion to cut the flesh away from the skin, working towards the head.^[4]

Deboning

If any bones remain in a fish fillet, use tweezers or pliers to grab them and pull them out of the flesh.^[4]^[5]

Techniques

Handling

In order to get the highest quality fish products, it is important to handle them correctly. The first trick is to very quickly cool fish after death in an ice slurry.^[5] It's also important to remember that fish will undergo rigor mortis after death—white-fleshed fish have a shorter period peaking around 4.5–6 hours post-death, while redder-fleshed fish have a longer period peaking around 6–8 hrs.^[6] After rigor sets in, avoid handling the fish until it is over. Otherwise, tearing of the flesh can occur, which yields a mushy and unappetizing texture.^[6]

Another technique called ikejime involves a series of steps during and after slaughter to produce higher quality fish.^[9] In ikejime, the fish is first euthanized quickly through the insertion of a spike into the hindbrain instead of letting it suffocate after capture. The fish is then rapidly and thoroughly bled out, which reduces the chance of bacterial breakdown. After a final step that involves the insertion of a wire into the spinal cord to destroy remaining nervous tissue, the fish is rapidly cooled in an ice slurry. This entire process extends the shelf life of the fish and improves the texture of the flesh.

Cooking

Overall, fish is quite delicate and easy to overcook.^[1]^[4] As it cooks quickly,^[1] look for the following tells to determine when it is just done:^[1]^[4]

The flesh turns from translucent to opaque;
The flesh starts to flake but does not yet flake easily;
The bone separates from the flesh and becomes very easy to remove

Cook fish at lower temperatures than you would meat.^[6] Remember that residual heat causes slight carryover cooking even after you remove it from the heat source,^[4]^[2] though fish does not need to be rested between cooking and serving.^[10]

Cooking methods

Fat fish are especially suited for baking, which is a dry-heat method, since it is harder to dry them out.^[1] Lean fish can also be baked, though they are at greater risk, and they need to be basted during the cooking.^[1]^[4] In order to get some color on large fish without overcooking, you can sear it on the stove before finishing in the oven^[4]—brown the presentation side first.^[1] Like baking, broiling and grilling are best suited for fat fish, though they can also be used on lean fish. Broiling is typically better for more delicate fish that could break apart on the grill.^[4] All fish varieties should be brushed with oil first—even fat fish.^[1]^[4]

Poaching is an excellent technique for lean fish because it is gentle and helps reduce moisture loss.^[1] Steaming is also great for lean fish for similar reasons.^[4] One particular way to steam fish is called "en papillote"—here, the fish plus any aromatic ingredients are enclosed in a pouch of parchment paper and heated.^[4] The parchment keeps the moisture in and causes the fish to steam in the aromatics.^[1]

Sautéing or pan-frying works well for most fish types, and lean fish especially benefits from the added fat.^[1] It's important here to use slices of fish that are of uniform size and thickness. Make sure the pan is hot and not overcrowded when the fish is added—if not, the fish will cook through before it has a chance to brown.^[4] Sprinkling some salt on the pan can help prevent sticking if this is a problem.^[7] Note that deep frying is best for lean fish only, as fat fish can get excessively greasy.^[1]

Sous vide cooking is excellent for fish, as it brings it to the exact desired temperature without a risk of overcooking.^[4] This gives the fish a very tender and melting quality.^[8] Avoid pressure-cooking fish, which tends to toughen it.^[1]

Use

Fish is eaten globally and in a huge array of preparations. In addition to the flesh, of which there is a lot, other parts like the tongues, heads, and livers may be eaten.^[2] Fish heads, for example, are eaten in some Asian cuisines fried or in soup.^[2] The head and bones also make good fish stock.^[5] Some cuisines feature raw fish, either chopped (e.g. tartare), sliced (carpaccio), marinated (ceviche), or served with rice (sushi).^[1]

In addition eating fish fresh, many cultures process it into different products. Curing and drying fish are common, and a large amount of dried seafood production and consumption occurs in Southeast Asia.^[2] When drying fish, note that fat fish are significantly more at risk for oxidation and the development of off flavors.^[2] For the same reasons, lean fish are typically dry cured while fat fish are brined to reduce the oxidation risk.^[5]

It is often fermented as well, either by simply salting it or combining it with fermenting grains.^[2]

Safety

When working with fish, it's important to keep a couple things in mind to ensure safety. One potential health risk from eating fish is infection with a parasite living within the fish flesh,^[2] which can occur by eating raw or rare fish. One way to eliminate this risk if you don't choose to cook the fish all the way through is to use fish that has been previously frozen, which kills the parasites.^[5] The rule of thumb here is to freeze for at least 7 days below –20°C (–4°F) or at least 15 hours below –35°C (–31°F).^[8] Note that freezing does not kill bacteria, though bacterial contamination usually occurs at the surface of the flesh and not significantly within it.^[8] To kill bacteria, the fish should be heated to 60°C/140°F or held for a sufficient period at 55°C/131°F.^[2]^[8] Unfortunately, heating does not necessarily eliminate any toxins produced by significant microbial contamination^[2]—fish that smells decayed cannot be made safe by heating. Similarly, environmental toxins can build up in some fish, especially large and long-living fish at the top of the food chain.^[2]^[11] For example, tuna, shark, and swordfish can have a high level of mercury accumulation in their flesh, and this is one source of mercury exposure for humans.^[11] In some unusual cases, ciguatera poisoning can occur by consuming contaminated tropical reef fish.^[2]

Generally speaking, the best way to prevent foodborne illness from fish is to use very fresh fish, to keep it cold, and to handle it as little as possible.^[1]^[8] For added protection when undercooking it, use previously frozen fish or a species that has a low risk of parasites.^[1]^[8]

Substitution

The following table indicates groups of fish that share characteristics and can often be reasonably substituted with each other:^[4]


White, tender, lean	White, tender to firm texture, lean to moderate fat	Light, some flavor, firmness, and fat	Darker, some flavor and firmness, fatty	Dark, strong flavor and firmness, fatty
Atlantic cod Dover sole Haddock Halibut Lake whitefish Pacific sand dab Pacific sole Spotted cabrilla Tilapia	American plaice Arrowtooth and starry flounder Butter, English, and rock sole Cobia John Dory Lionfish Sea bream Sea trout	Alaskan pollock Brook and rainbow trout Catfish Grouper Mahi mahi Pacific ocean perch Red snapper Skate White sea bass Wahoo/Ono	Arctic char (lake trout) Atlantic, coho, king salmon European Turbot Eel Herring Lake Chub Lake sturgeon Monkfish Pacific cod Pollock Striped bass Swordfish Vermillion snapper	Black sea bass Bluefish King mackerel Spanish mackerel Tuna