Fisheries and Aquaculture

Advantages and Drawbacks of Aquaculture

Seafood and Health

Health Benefits

Health Hazards

Life in Water and the Special Nature of Fish

The Paleness and Tenderness of Fish Flesh

The Flavor of Fish and Shellfish

The Healthfulness of Fish Oils

The Perishability of Fish and Shellfish

The Sensitivity and Fragility of Fish in the Pan

The Unpredictability of Fish Quality

The Anatomy and Qualities of Fish

Fish Anatomy

Fish Muscle and Its Delicate Texture

Fish Flavor

Fish Color

The Fish We Eat

The Herring Family: Anchovy, Sardine, Sprat, Shad

Carp and Catfish

Salmons, Trouts, and Relatives

The Cod Family

Nile Perch and Tilapia

Basses

Icefish

Tunas and Mackerel

Swordfish

Flatfish: Soles, Turbot, Halibuts, Flounders

From the Waters to the Kitchen

The Harvest

The Effects of Rigor Mortis and Time

Recognizing Fresh Fish

Storing Fresh Fish and Shellfish: Refrigeration and Freezing

Irradiation

Unheated Preparations of Fish and Shellfish

Sushi and Sashimi

Tart Ceviche and Kinilaw

Salty Poke and Lomi

Cooking Fish and Shellfish

How Heat Transforms Raw Fish

Preparations for Cooking

Techniques for Cooking Fish and Shellfish

Fish Mixtures

Shellfish and Their Special Qualities

Crustaceans: Shrimps, Lobsters, Crabs, and Relatives

Molluscs: Clams, Mussels, Oysters, Scallops, Squid, and Relatives

Other Invertebrates: Sea Urchins

Preserved Fish and Shellfish

Dried Fish

Salted Fish

Fermented Fish

Smoked Fish

Four-Way Preservation: Japanese Katsuobushi

Marinated Fish

Canned Fish

Fish Eggs

Salt Transforms Egg Flavor and Texture

Caviar

Fish and shellfish are foods from the earth’s other world, its vast water underworld. Dry land makes up less than a third of the planet’s surface, and it’s a tissue-thin home compared to the oceans, whose floor plunges as much as 7 miles below the waves. The oceans are voluminous and ancient, the “primordial soup” in which all life began, and in which the human imagination has found rich inspiration for myths of destruction and creation, of metamorphosis and rebirth. The creatures that live in this cold, dark, dense, airless place are unmatched among our food animals in their variety and their strangeness.

Our species has long nourished itself on fish and shellfish, and it built nations on them as well. The world’s coastlines are dotted with massive piles of oyster and mussel shells that commemorate feasts going back 300,000 years. By 40,000 years ago the hunters of prehistoric Europe were carving salmon images and making the first hooks to catch river fish; and not long afterward, they ventured onto the ocean in boats. From the late Middle Ages on, the seagoing nations of Europe and Scandinavia exploited the Atlantic’s abundant stocks of cod and herring, drying and salting them into commodities that were the foundation of their modern prosperity.

Five hundred years later, at the beginning of the 21st century, the oceans’ productivity is giving out. It has been exhausted by feeding a tenfold increase in the human population, and by constant advances in fishing technology and efficiency. With the help of faster and larger ships, sonar to see into the depths, miles-long nets and lines, and the mechanization of all aspects of the harvest, we’ve managed to fish many important food species to the verge of commercial extinction. Formerly common fish — cod and herring, Atlantic salmon and swordfish and sole, sturgeon and shark — are increasingly rare. Others — orange roughy, Chilean sea bass, monkfish — come and go from the market, temporarily abundant until they too are overfished.

The decline in the populations of wild fish has encouraged the widespread revival and modernization of aquaculture. Fish farms are now our nearly exclusive source for freshwater fish, for Atlantic salmon, and for mussels. Many of these operations effectively spare wild populations, but others further deplete them and cause environmental damage of their own. It takes some effort these days to find and choose fish and shellfish that have been produced in environmentally responsible, sustainable ways.

Yet it’s a good time to be eating from the waters. More fish of excellent quality are available more widely than ever before, and they come from all over the globe, offering the opportunity to discover new ingredients and new pleasures. At the same time, their variety and variability make it challenging to choose and prepare them well. Fish and shellfish are more fragile and less predictable than ordinary meats. This chapter will take a close look at their special nature, and how they’re best handled and prepared.

Fisheries
and Aquaculture

Of all our foods, fish and shellfish are the only ones that we still harvest in significant quantities from the wild. The history of the world’s fisheries is the saga of human ingenuity, bravery, hunger, and wastefulness evolving into a maw that now swallows much of the oceans’ tremendous productivity. In 1883, the eminent biologist T. H. Huxley expressed his belief that “the cod fishery, the herring fishery, the pilchard fishery, the mackerel fishery, and probably all the great sea fisheries are inexhaustible; that is to say that nothing we do seriously affects the numbers of fish.” Just over a century later, cod and herring stocks on both sides of the North Atlantic have collapsed, many other fish are in decline, and the U.N. Food and Agriculture Organization estimates that we are harvesting two-thirds of the major commercial fish in the world at or beyond the level at which they can sustain themselves.

In addition to dangerously depleting its target fish populations, modern fishing causes collateral damage to other species, the “bycatch” of undiscriminating nets and lines that is simply discarded, and it can damage ocean-bottom habitats. Fishing is also an unpredictable, dangerous job, subject to the uncertainties of weather and the hazards of working at sea with heavy equipment. To this highly problematic system of production, there is an increasingly important alternative: aquaculture, or fish farming, which in many parts of the world goes back thousands of years. Today in the United States, all of the rainbow trout and nearly all of the catfish sold are farmed on land in various kinds of ponds and tanks. Norway pioneered the ocean farming of Atlantic salmon in large offshore pens in the 1960s; and today more than a third of the salmon eaten in the world is farmed in Europe and North and South America. About a third of the world warm-water shrimp harvest is cultured, mainly in Asia. In all, about 70 species are now farmed worldwide.

Advantages and Drawbacks of Aquaculture

There are several distinct advantages to aquaculture. Above all, it allows the producer unequaled control over the condition of the fish and the circumstances of the harvest, both of which can result in better quality in the market. Farmed fish can be carefully selected for rapid growth and other desirable characteristics, and raised to a uniform and ideal stage for eating. By adjusting water temperature and flow rate and light levels, fish can be induced to grow far more rapidly than in the wild, and a balance can be struck between energy consumption and muscle-toning exercise. Farmed fish are often fattier and so more succulent. They can be slaughtered without suffering the stress and physical damage of being hooked, netted, or dumped en masse on deck; and they can be processed and chilled immediately and cleanly, thus prolonging their period of maximum quality.

However, aquaculture is not a perfect solution to the problems of ocean fishing, and has itself created a number of serious problems. Farming in offshore pens contaminates surrounding waters with wastes, antibiotics, and unconsumed food, and allows genetically uniform fish to escape and dilute the diversity of already endangered wild populations. The feed for carnivorous and scavenger species (salmon, shrimp) is mainly protein-rich fish meal, so some aquaculture operations actually consume wild fish rather than sparing them. And very recent studies have found that some environmental toxins (PCBs, p. 184) become concentrated in fish meal and are deposited in the flesh of farmed salmon.

A less serious problem, but one that makes a difference in the kitchen, is that the combination of limited water flow, limited exercise, and artificial feeds can affect the texture and flavor of farmed fish. In taste tests, farmed trout, salmon, and catfish are perceived to be blander and softer than their wild counterparts.

Modern aquaculture is still young, and ongoing research and regulation will certainly solve some of these problems. In the meantime, the most environmentally benign products of aquaculture are freshwater fish and a few saltwater fish (sturgeon, turbot) farmed on land, and molluscs farmed on seacoasts. Concerned cooks and consumers can get up-to-date information about the health of fisheries and aquacultural practices from a number of public interest groups, including the Monterey Bay Aquarium in California.

Seafood and Health

Fish is good for us: this belief is one important reason for the growing consumption of seafood in the developed world. There is indeed good evidence that fish oils can contribute significantly to our long-term health. On the other hand, of all our foods, fish and shellfish are the source of the broadest range of immediate health hazards, from bacteria and viruses to parasites, pollutants, and strange toxins. Cooks and consumers should be aware of these hazards, and of how to minimize them. The simplest rule is to buy from knowledgeable seafood specialists whose stock turns over quickly, and to cook fish and shellfish promptly and thoroughly. Raw and lightly cooked preparations are delicious but carry the risk of several kinds of food-borne disease. They are best indulged in at established restaurants that have access to the best fish and the expertise to prepare it.

Health Benefits

Like meats, fish and shellfish are good sources of protein, the B vitamins, and various minerals. Iodine and calcium are special strengths. Many fish are very lean, and so offer these nutrients along with relatively few calories. But the fat of ocean fish turns out to be especially valuable in its own right. Like other fats that are liquid at room temperature, fish fats are usually referred to as “oils.”

The Benefits of Fish Oils As we’ll see (p. 189), life in cold water has endowed sea creatures with fats rich in unusual, highly unsaturated omega-3 fatty acids. (The name means that the first kink in the long chain of carbon atoms is at the third link from the end; see p. 801.) The human body can’t make these fatty acids very efficiently from other fatty acids, so our diet supplies most of them. A growing body of evidence indicates that they happen to have a number of beneficial influences on our metabolism.

One benefit is quite direct, the others indirect. Omega-3 fatty acids are essential to the development and function of the brain and the retina, and it appears that an abundance in our diet helps ensure the health of the central nervous system in infancy and throughout life. But the body also transforms omega-3 fatty acids into a special set of calming immune-system signals (eicosanoids). The immune system responds to various kinds of injuries by generating an inflammation, which kills cells in the vicinity of the injury in preparation for repairing it. But some inflammations can become self-perpetuating, and do more harm than good: most importantly, they can damage arteries and contribute to heart disease, and they can contribute to the development of some cancers. A diet rich in omega-3 fatty acids helps limit the inflammatory response, and thus lowers the incidence of heart disease and cancer. By reducing the body’s readiness to form blood clots, it also lowers the incidence of stroke. And it lowers the artery-damaging form of blood cholesterol.

In sum, it looks as though a moderate and regular consumption of fatty ocean fish is good for us in several ways. Fish obtain their omega-3 fatty acids directly or indirectly from tiny oceanic plants called phytoplankton. Farmed fish generally have lower levels of the omega-3s in their formulated feed, and so less in their meat. Freshwater fish don’t have access to the oceanic plankton, and so provide negligible amounts of omega-3s. However, all fish contain low amounts of cholesterol-raising saturated fats, so to the extent that they replace meat in the diet, they lower artery-damaging blood cholesterol and reduce the risk of heart disease.

Health Hazards

There are three general kinds of hazardous materials that contaminate fish and shellfish: industrial toxins, biological toxins, and disease-causing microbes and parasites.

Toxic Metals and Pollutants Because rain washes chemical pollution from the air to the ground, and rain and irrigation wash it from the ground, almost every kind of chemical produced on the planet ends up in the rivers and oceans, where they can be accumulated by fish and shellfish. Of the potentially hazardous substances found in fish, the most significant are heavy metals and organic (carbon-containing) pollutants, preeminently dioxins and polychlorinated biphenyls, or PCBs. The heavy metals, including mercury, lead, cadmium, and copper, interfere with oxygen absorption and the transmission of signals in the nervous system; they’re known to cause brain damage in humans. Organic pollutants cause liver damage, cancer, and hormonal disturbances in laboratory animals, and they accumulate in body fat. Fatty coho salmon and trout in the Great Lakes carry such high levels of these pollutants that government agencies advise against eating them.

Cooking doesn’t eliminate chemical toxins, and there’s no direct way for consumers to know whether fish contain unhealthy levels of them. In general, they concentrate in filter-feeding shellfish like oysters, which strain suspended particles from large volumes of water, and in large predatory fish at the top of the food chain, which are long-lived and eat other creatures that accumulate toxins. In recent years, common ocean fish have been found to contain so much mercury that the U.S. Food and Drug Administration advises children and pregnant women not to eat any swordfish, shark, tilefish, and king mackerel, and to limit their overall fish consumption to 12 ounces/335 grams per week. Even tuna, currently the most popular seafood in the United States after shrimp, may join the list of fish that are best eaten only occasionally. The fish least likely to accumulate mercury and other toxins are smaller, short-lived fish from the open ocean and from farms with a controlled water supply. They include Pacific salmon and soles, common mackerel, sardines, and farmed trout, striped bass, catfish, and tilapia. Sport fishing in freshwater or near large coastal cities is more likely to land an unwholesome catch contaminated by runoff or industrial discharge.

Infectious and Toxin-Producing Microbes Seafoods carry about the same risk of bacterial infections and poisonings as other meats (p. 125). The riskiest seafoods are raw or undercooked shellfish, particularly bivalves, which trap bacteria and viruses as they filter the water for food, and which we eat digestive tract and all, sometimes raw. As early as the 19th century, public health officials connected outbreaks of cholera and typhoid fever with shellfish from polluted waters. Government monitoring of water quality and regulation of shellfish harvest and sales have greatly reduced these problems in many countries. And scrupulous restaurant owners make sure to buy shellfish for the summer raw bar from monitored sources, or from less risky cold-water sources. But lovers of raw or lightly cooked seafood should be aware of the possibility of infection.

As a general rule, infections by bacteria and parasites can be prevented by cooking seafood to a minimum of 140ºF/60ºC. Temperatures above 185ºF/82ºC are required to eliminate some viruses. Some chemical toxins produced by microbes survive cooking, and can cause food poisoning even though the microbes themselves are destroyed.

Among the most important microbes in fish and shellfish are the following:

• Vibrio bacteria, natural inhabitants of estuary waters that thrive in warm summer months. One species causes cholera, another a milder diarrheal disease, and a third (V. vulnificus), usually contracted from raw oysters and the deadliest of the seafood-related diseases, causes high fever, a drop in blood pressure, and damage to skin and flesh, and kills more than half of its victims.
• Botulism bacteria, which grow in the digestive system of unchilled fish and produce a deadly nerve toxin. Most cases of fish-borne botulism are caused by improperly cold-smoked, salt-cured, or fermented products.
• Intestinal viruses, the “Norwalk” viruses, which attack the lining of the small intestine and cause vomiting and diarrhea.
• Hepatitis viruses A and E, which can cause long-lasting liver damage.

Scombroid Poisoning Scombroid poisoning is unusual in that it is caused by a number of otherwise harmless microbes when they grow on insufficiently chilled mackerels of the genus Scomber and other similarly active swimmers, including tuna, mahimahi, bluefish, herring, sardine, and anchovy. Within half an hour of eating one of these contaminated fish, even fully cooked, the victim suffers from temporary headache, rash, itching, nausea, and diarrhea. The symptoms are apparently caused by a number of toxins including histamine, a substance that our cells use to signal each other in response to damage; antihistamine drugs give some relief.

Shellfish and Ciguatera Poisonings Fish and shellfish share the waters with many thousands of animal and plant species, some of which engage in nasty chemical warfare with each other. At least 60 species of one-celled algae called dinoflagellates produce defensive toxins that also poison the human digestive and nervous systems. Several of these toxins can kill.

We don’t consume dinoflagellates directly, but we do eat animals that eat them. Bivalve filter feeders — mussels, clams, scallops, oysters — concentrate algal toxins in their gills and/or digestive organs, and then transmit the poisons to other shellfish — usually crabs and whelks — or to humans. Accordingly, most dinoflagellate poisonings are called “shellfish poisonings.” Many countries now routinely monitor waters for the algae and shellfish for the toxins, so the greatest risk is from shellfish gathered privately.

There are several distinct types of shellfish poisoning, each caused by a different toxin and each with somewhat different symptoms (see box below), though all but one are marked by tingling, numbness, and weakness within minutes to hours after eating. Dinoflagellate toxins are not destroyed by ordinary cooking, and some actually become more toxic when heated. Suspect shellfish should therefore be avoided altogether.

Finfish generally don’t accumulate toxins from algae. The exceptions are a group of tropical reef fish — barracuda, groupers, jacks, king mackerel, mahimahi, mullets, porgies, snappers, wahoo — that prey on an algae-eating snail (cigua) and can cause ciguatera poisoning.

Parasites Parasites are not bacteria or viruses: they’re animals, from single-celled protozoa to large worms, that take up residence in one or more animal “hosts” and use them for both shelter and nourishment during parts of their life cycle. There are more than 50 that can be transmitted to people who eat fish raw or undercooked, a handful of which are relatively common, and may require surgery to remove. Thanks to their more complex biological organization, parasites are sensitive to freezing (bacteria generally aren’t). So there’s a simple rule for eliminating parasites in fish and shellfish: either cook the food to a minimum of 140ºF/60ºC, or prefreeze it. The U.S. FDA recommends freezing at –31ºF/–35ºC for 15 hours, or –10ºF/–23ºC for seven days, treatments that are not feasible in home freezers, which seldom dip below 0ºF.

Poisonings Caused by Toxic Algae

Type of Poisoning

Usual Regions

Diarrhetic shellfish poisoning

Japan, Europe, Canada

Amnesic shellfish poisoning

U.S. Pacific coast, New England

Neurotoxic shellfish poisoning

Gulf of Mexico, Florida

Paralytic shellfish poisoning

U.S. Pacific coast, New England

Ciguatera poisoning

Caribbean, Hawaii, South Pacific

Type of Poisoning

Usual Sources

Diarrhetic shellfish poisoning

Mussels, scallops

Amnesic shellfish poisoning

Mussels, clams, Dungeness crab

Neurotoxic shellfish poisoning

Clams, oysters

Paralytic shellfish poisoning

Clams, mussels, oysters, scallops, cockles

Ciguatera poisoning

Barracuda, grouper, snapper, other reef fish

Type of Poisoning

Toxins

Diarrhetic shellfish poisoning

Okadaic acid

Amnesic shellfish poisoning

Domoic acid

Neurotoxic shellfish poisoning

Brevetoxins

Paralytic shellfish poisoning

Saxitoxins

Ciguatera poisoning

Ciguatoxins

Anisakid and Cod Worms These species of Anisakis and Pseudoterranova can be an inch/2.5 centimeters or more long, with a diameter of a few human hairs. Both often cause only a harmless tingling in the throat, but they sometimes invade the lining of the stomach or small intestine and cause pain, nausea, and diarrhea. They’re commonly found in herring, mackerel, cod, halibut, salmon, rockfish, and squid, and can be contracted from sushi or lightly marinated, salted, or cold-smoked preparations. Farmed salmon are much less likely to be infected than wild salmon.

Tapeworms and Flukes Larvae of the tapeworm Diphyllobothrium latum, which can grow in the human intestine to as long as 27 feet/9 meters, are found in freshwater fish of temperate regions worldwide. Notable among these is the whitefish, which caused many infections when home cooks made the traditional Jewish dish gefilte fish and tasted the raw mix to correct the seasoning.

More serious hazards are a number of flukes, or flatworms, which are carried by fresh- and brackish-water crayfish, crabs, and fish. They damage the human liver and lungs after being consumed in such live Asian delicacies as “jumping salad” and “drunken crabs.”

Potential Carcinogens Formed During Fish Preparation Certain cooking processes transform the proteins and related molecules in meat and fish into highly reactive products that damage DNA and may thereby initiate the development of cancers (p. 124). So the rule for cooking meat also holds for cooking fish: to minimize the creation of potential carcinogens, steam, braise, and poach fish rather than grilling, broiling, or frying it. If you do use high, dry heat, then consider applying a marinade, whose moisture, acidity, and other chemical qualities reduce carcinogen production.

Life in Water and
the Special Nature of Fish

As a home for living things, the earth’s waters are a world apart. The house rules are very different than they are for our cattle and pigs and chickens. The adaptations of fish and shellfish to life in water are the source of their distinctive qualities as foods.

The Paleness and Tenderness of Fish Flesh

Fish owe their small, light bones, delicate connective tissue, and large, pale muscle masses to the fact that water is much denser than air. Fish can attain a neutral buoyancy — can be almost weightless — simply by storing some lighter-than-water oils or gas in their bodies. This means that they don’t need the heavy skeletons or the tough connective tissues that land animals have developed in order to support themselves against the force of gravity.

The paleness of fish flesh results from water’s buoyancy and its resistance to movement. Continuous cruising requires long-term stamina and is therefore performed by slow-twitch red fibers, well supplied with the oxygen-storing pigment myoglobin and fat for fuel (p. 132). Since cruising in buoyant water is relatively effortless, fish devote between a tenth and a third of their muscle to that task, usually a thin dark layer just under the skin. But water’s resistance to movement increases exponentially with the fish’s speed. This means that fish must develop very high power very quickly when accelerating. And so they devote most of their muscle mass to an emergency powerpack of fast-twitch white cells that are used only for occasional bursts of rapid movement.

In addition to red and white muscle fibers, fish in the tuna family and some others have intermediate “pink” fibers, which are white fibers modified for more continuous work with oxygen-storing pigments.

The Flavor of Fish
and Shellfish

The flavors of ocean and freshwater creatures are very different. Because ocean fish breathe and swallow salty water, they had to develop a way of maintaining their body fluids at the right concentration of dissolved substances. Water in the open ocean is about 3% salt by weight, while the optimum level of dissolved minerals inside animal cells, sodium chloride included, is less than 1%. Most ocean creatures balance the saltiness of seawater by filling their cells with amino acids and their relatives the amines. The amino acid glycine is sweet; glutamic acid in the form of monosodium glutamate is savory and mouthfilling. Shellfish are especially rich in these and other tasty amino acids. Finfish contain some, but also rely on a largely tasteless amine called TMAO (trimethylamine oxide). And sharks, skates, and rays use a different substance: slightly salty and bitter urea, which is what animals generally turn protein waste into in order to excrete it. The problem with TMAO and urea is that once the fish are killed, bacteria and fish enzymes convert the former into stinky TMA (trimethylamine) and the latter into kitchen-cleanser ammonia. They’re thus responsible for the powerfully bad smell of old fish.

Fish muscle tissues, shown in cross-section. Below left: Most fish swim intermittently, so their muscle mass consists mainly of fast white fibers, with isolated regions of slow red fibers. Center: Tuna swim more continuously and contain larger masses of dark fibers, while even their white fibers contain some myoglobin. Right: Soles, halibuts, and other bottom-hugging flatfish swim on their side.

Freshwater fish are a different story. Their environment is actually less salty than their cells, so they have no need to accumulate amino acids, amines, or urea. Their flesh is therefore relatively mild, both when it’s fresh and when it’s old.

The Healthfulness
of Fish Oils

Why should fish and not Angus steers provide the highly unsaturated fats that turn out to be good for us? Because oceanic waters are colder than pastures and barns, and most fish are cold-blooded. Throw a beefsteak in the ocean and it congeals; its cells are designed to operate at the animal’s usual body temperature, around 100ºF/40ºC. The cell membranes and energy stores of ocean fish and the plankton they eat must remain fluid and workable at temperatures that approach 32ºF/0ºC. Their fatty acids are therefore very long and irregular in structure (p. 801), and don’t solidify into orderly crystals until the temperature gets very low indeed.

The Perishability of Fish
and Shellfish

The cold aquatic environment is also responsible for the notorious tendency of fish and shellfish to spoil faster than other meats. The cold has two different effects. First, it requires fish to rely on the highly unsaturated fatty acids that remain fluid at low temperatures: and these molecules are highly susceptible to being broken by oxygen into stale-smelling, cardboardy fragments. More importantly, cold water requires fish to have enzymes that work well in the cold, and the bacteria that live in and on the fish also thrive at low temperatures. The enzymes and bacteria typical of our warm-blooded meat animals normally work at 100ºF/40ºC, and are slowed to a crawl in a refrigerator at 40ºF/5ºC. But the same refrigerator feels perfectly balmy to deep-water fish enzymes and spoilage bacteria. And among fishes, cold-water species, especially fatty ones, spoil faster than tropical ones. Where refrigerated beef will keep and even improve for weeks, mackerel and herring remain in good condition on ice for only five days, cod and salmon for eight, trout for 15, carp and tilapia (a freshwater African native) for 20 days.

The Sensitivity and Fragility
of Fish in the Pan

Most fish pose a double challenge in the kitchen. They are more easily overcooked to a dry fibrousness than ordinary meats. And even when they’re perfectly done, their flesh is very fragile and tends to fall apart when moved from pan or grill to plate. The sensitivity of fish to heat is related to their perishability: muscle fibers that are specialized to work well in the cold not only spoil at lower temperatures, they become cooked at lower temperatures. The muscle proteins of ocean fish begin to unfold and coagulate at room temperature!

Though overcooked fish gets dry, it never gets tough. The fragility of cooked fish results from its relatively small amounts connective-tissue collagen, and from the low temperature at which that collagen is dissolved into gelatin.

The Unpredictability
of Fish Quality

The quality of many fish and shellfish can vary drastically from season to season. This is because they live out life cycles that typically include one phase during which they grow and mature, accumulating energy reserves and reaching their peak of culinary quality, and a subsequent phase during which they expend those reserves to migrate and create masses of eggs or sperm for the next generation. And most fish don’t store their reserves in layers of fat, as land animals do. Instead they use the proteins of their muscle mass as their energy pack. During migrations and spawning, they accumulate protein-digesting enzymes in their muscle and literally transform their own flesh into the next generation. Then and afterward, their muscle is meager and spent, and makes a spongy, mushy dish.

Because different fish have different cycles, and can be in different phases depending on the part of the world in which they’ve been caught, it’s often hard to know whether a given wild fish in the market is at its prime.

The Anatomy
and Qualities of Fish

Fish and shellfish have many things in common, but anatomy is not one of them. Fish are vertebrates, animals with backbones; shellfish are boneless invertebrates. Their muscles and organs are organized differently, and as a result they can have very different textures. The anatomy and special qualities of shellfish are described separately, beginning on p. 218.

Fish Anatomy

For about 400 million years, beginning well before reptiles or birds or mammals had even made an appearance, fish have had the same basic body plan: a streamlined bullet shape that minimizes the water’s resistance to their movement. There are exceptions, but most fish can be thought of as sheets of muscle tissue anchored with connective tissue and the backbone to a propulsive tail. The animals push water behind them, developing thrust by undulations of the whole body and flexing of the tail.

Skin and Scales Fish skin consists of two layers, a thin outer epidermis and a thicker underlying dermis. A variety of gland cells in the epidermis secrete protective chemicals, the most evident of which is mucus, a proteinaceous substance much like egg white. The skin is often richer than the flesh, averaging 5–10% fat. The thick dermis layer of the skin is especially rich inconnective tissue. It’s generally about one-third collagen by weight, and therefore can contribute much more thickening gelatin to stocks and stews than the fish’s flesh (0.3–3% collagen) or bones. Moist heating will turn the skin into a slick gelatinous sheet, while frying or grilling enough to desiccate it will make it crisp.

Scales are another evident form of protection for the fish skin. They are made up of the same hard, tough calcareous minerals as teeth, and are removed by scraping against their grain with a knife blade.

Bones The main skeleton of a small or moderate-size fish, consisting of the backbone and attached rib cage, can often be separated from the meat in one piece. However, there are usually also bones projecting into the fins, and fish in the herring, salmon, and other families have small “floating” or “pin” bones unattached to the main skeleton, which help stiffen some of the connective-tissue sheets and direct the muscular forces along them. Because fish bones are smaller, lighter, and less mineralized with calcium than land-animal bones, and because their collagen is less tough, they can be softened and even dissolved by a relatively short period near the boil (hence the high calcium content of canned salmon). Fish skeletons are even eaten on their own: in Catalonia, Japan, and India they’re deep-fried until crunchy.

Fish Innards The innards of fish and shellfish offer their own special pleasures. Fish eggs are described below (p. 239). Many fish livers are prized, including those of the goatfish (“red mullet”), monkfish, mackerel, ray, and cod, as is the comparable organ in crustaceans, the hepatopancreas (p. 219). The “tongues” of cod and carp are actually throat muscles and associated connective tissue that softens with long cooking. Fish heads can be 20% fatty material and are stuffed and slow-cooked until the bones soften. And then there are “sounds,” or swim bladders, balloons of connective tissue that such fish as cod, carp, catfish, and sturgeon fill with air to adjust their buoyancy. In Asia, fish sounds are dried, fried until they puff up, and slowly cooked in a savory sauce.

Fish Muscle and its Delicate Texture

Fish have a more delicate texture than the flesh of our land animals. The reasons for this are the layered structure of fish muscle, and the sparseness and weakness of fish connective tissue.

Muscle Structure In land animals, individual muscles and muscle fibers can be quite long, on the order of several inches, and the muscles taper down at the ends into a tough tendon that connects them to bone. In fish, by contrast, muscle fibers are arranged in sheets a fraction of an inch thick (“myotomes”), and each short fiber merges into very thin layers of connective tissue (“myosepta”), which are a loose mesh of collagen fibers that run from the backbone to the skin. The muscle sheets are folded and nested in complex W-like shapes that apparently orient the fibers for greatest efficiency of force transmission to the backbone. There are about 50 muscle sheets or “flakes” along the length of a cod.

Connective Tissue Fish connective tissue is weak because its collagen contains less structure-reinforcing amino acids than beef collagen does, and because the muscle tissue also serves as an energy store that’s repeatedly built up and broken down, whereas in land animals it is progressively reinforced with age. Meat collagen is tough and must be cooked for some time near the boil to be dissolved into gelatin, but in most fish it dissolves at 120 or 130ºF/50–55ºC, at which point the muscle layers separate into distinct flakes.

Succulence from Gelatin and Fat Both gelatin and fat can contribute an impression of moistness to fish texture. Fish with little collagen — trout, bass — seem drier when cooked than those with more — halibut, shark. Because the motion for steady swimming comes mostly from the back end of the fish, the tail region contains more connective tissue than the head end, and seems more succulent. Red muscle fibers are thinner than white fibers and require more connective tissue to join them with each other, so dark meat has a noticeably finer, more gelatinous texture.

The fat content of fish muscle runs a tremendous range, from 0.5% in cod and other white fish to 20% in well-fed herring and their relatives (p. 184). Fat storage cells are found primarily in a distinct layer under the skin, and then in the visible sheets of connective tissue that separate the myotomes. Within a given fish, the belly region is usually the fattiest, while muscle segments get progressively leaner toward the back and tail. A center-cut salmon steak may have twice the fat content of a slice from the tail.

Fish anatomy. Unlike the muscles of land animals (p. 120), fish muscles are arranged in layers of short fibers, and organized and separated by sheets of connective tissue that are thin and delicate.

Softness Certain conditions can lead to fish flesh becoming unpleasantly soft. When fish flesh is depleted by migration or by spawning, their sparse muscle proteins bond to each other only very loosely, and the overall texture is soft and flabby. In extreme cases, such as “sloppy” cod or “jellied” sole, the muscle proteins are so tenuously bonded that the muscle seems almost liquefied. Some fish come out mushy when thawed after frozen storage, because freezing disrupts the cells’ compartments and liberates enzymes that then attack the muscle fibers. And enzyme activity during cooking can turn firm fish mushy in the pan; see p. 211.

Fish Flavor

The flavor of fish may well be the most variable and changeable among our basic foods. It depends on the kind of fish, the salinity of its home waters, the food it eats, and the way it is harvested and handled.

Fish Taste In general, seafood is more full-tasting than meats or freshwater fish, because ocean creatures accumulate amino acids to counterbalance the salinity of seawater (p. 188). The flesh of ocean fish generally contains about the same amount of salty sodium as beef or trout, but three to ten times more free amino acids, notably sweet glycine and savory glutamate. Shellfish, sharks and rays, and members of the herring and mackerel family are especially rich in these amino acids. Because the salt content of seawater varies substantially — it’s high in the open ocean, lower near river mouths — the amino-acid content and therefore taste intensity of fish varies according to the waters they’re caught in.

An additional element of fish taste is contributed indirectly by the energy-carrying compound ATP (adenosine triphosphate). When a cell extracts energy from ATP, it is transformed into a series of smaller molecules, one of which, IMP (inosine monophosphate), has a savory taste similar to that of glutamate. However, IMP is a transient substance. So the savoriness of fish increases for some time after its death as IMP levels rise, then declines again as IMP disappears.

Fish Aroma

Fresh and Plant-like Few of us get the chance to enjoy the experience, but very fresh fish smell surprisingly like crushed plant leaves! The fatty materials of both plants and fish are highly unsaturated, and both leaves and fish skin have enzymes (lipoxygenases) that break these large smellless molecules down into the same small, aromatic fragments. Nearly all fish emit fragments (8 carbon atoms long) that have a heavy green, geranium-leaf, slightly metallic smell. Freshwater fish also produce fragments that are typical of freshly cut grass (6 carbons), and earthy fragments also found in mushrooms (8 carbons). Some freshwater and migratory species, especially the smelts, produce fragments characteristic of melons and cucumbers (9 carbons).

Smell of the Seacoast Ocean fish often have an additional, characteristic aroma of the seacoast. This ocean aroma appears to be provided by compounds called bromophenols, which are synthesized by algae and some primitive animals from bromine, an abundant element in seawater. Bromophenols are propelled into the seacoast air by wave action, where we smell them directly. Fish also accumulate them, either by eating algae or by eating algae eaters, and the fish can thus remind us of the sea air. Farmed saltwater fish lack the oceanic aroma unless their artificial feed is supplemented with bromophenols.

Muddiness Freshwater fish sometimes carry an unpleasant muddy aroma. It’s most often encountered in bottom-feeding fish, especially catfish and carp that are raised in ponds dug directly in the earth. The chemical culprits are two compounds that are produced by blue-green algae, especially in warm weather (geosmin and methylisoborneol). These chemicals appear to concentrate in the skin and the dark muscle tissue, which can be cut away to make the fish more palatable. Geosmin breaks down in acid conditions, so there is a good chemical reason for traditional recipes that include vinegar and other acidic ingredients.

Fishiness The moment fish are caught and killed, other aromas begin to develop. The strong smell that we readily identify as “fishy” is largely due to the saltwater-balancing compound TMAO (p. 188), which bacteria on the fish surfaces slowly break down to smelly TMA. Freshwater fish generally don’t accumulate TMAO, and crustaceans accumulate relatively little, so they don’t get as fishy as ocean fish. In addition, the unsaturated fats and fresh-smelling fragments (aldehydes) produced from them slowly react to produce other molecules with stale, cheesy characters, some of which accentuate the fishiness of TMA. And during frozen storage, the fish’s own enzymes also convert some TMA to DMA (dimethylamine), which smells weakly of ammonia.

Fortunately, the fishiness of fish past its prime can be greatly reduced a couple of simple treatments. TMA on the surface can be rinsed off with tap water. And acidic ingredients — lemon juice, vinegar, tomatoes — help in two ways. They encourage the stale fragments to react with water and become less volatile; and they contribute a hydrogen ion to TMA and DMA, which thereby take on a positive electrical charge, bond with water and other nearby molecules, and never escape the fish surface to enter our nose.

The aromas of cooked fish are discussed on p. 208.

Fish Color

Pale Translucence Most of the muscle in most raw fish is white or off-white and delicately translucent compared to raw beef or pork, whose cells are surrounded by more light-scattering connective tissue and fat cells. Especially fatty portions of fish, such as salmon and tuna bellies, look distinctly milky compared to flesh from just a few inches away. The translucence of fish muscle is turned into opacity by cooking treatments that cause the muscle proteins to unfold and bond to each other into large, light-scattering masses. Both heat and marination in acid unfold proteins and turn fish flesh opaque.

Red Tunas The meaty color of certain tunas is caused by the oxygen-storing pigment myoglobin (p. 132), which these fish need for their nonstop, high-velocity life (p. 201). Fish myoglobin is especially prone to being oxidized to brownish metmyoglobin, especially at freezer temperatures down to –22ºF/–30ºC; tuna must be frozen well below this to keep its color. During cooking, fish myoglobins denature and turn gray-brown at around the same temperature as beef myoglobin, between 140 and 160ºF/60 and 70ºC. Because they are often present in small quantities, their color change can be masked by the general milkiness caused when all the other cell proteins unfold and bond to each other. This is why fish with distinctly pink raw flesh (albacore tuna, mahimahi) will turn as white as any white fish when cooked.

Orange-Pink Salmons and Trouts The characteristic color of the salmons is due to a chemical relative of the carotene pigment that colors carrots. This compound, astaxanthin, comes from the salmons’ small crustacean prey, which create it from the beta-carotene they obtain from algae. Many fish store astaxanthin in their skin and ovaries, but only the salmon family stores it in muscle. Because farmed salmon and trout don’t have access to the wild crustaceans, they have paler flesh unless their feed is supplemented (usually with crustacean shell by-products or an industrially produced carotenoid called canthaxanthin).

The Fish We Eat

The number of different kinds of fish in the world is staggering. Of all the animals that have backbones, fish account for more than half, something approaching 29,000 species. Our species regularly eats hundreds of these. Perhaps two dozen are at least occasionally available in U.S. supermarkets, and another several dozen in upscale and ethnic restaurants, often under a variety of names. The box beginning on p. 195 surveys the family relations of some commonly eaten fish, and the paragraphs that follow provide a few details about the more important families.

Shellfish are also a diverse group of animals. They lack backbones and differ from finfish in important ways, so they’re described separately, p. 218.

The Herring Family:
Anchovy, Sardine,
Sprat, Shad

The herring family is an ancient, successful, and highly productive one, and for centuries was the animal food on which much of northern Europe subsisted. Its various species school throughout the world’s oceans in large, easily netted numbers and are relatively small, often just a few inches long but sometimes reaching 16 in/40 cm and 1.5 lb/0.75 kg.

Members of the herring family feed by constantly swimming and straining tiny zooplankton from the seawater. They thus have very active muscle and digestive enzymes that can soften their flesh and generate strong flavors soon after they’re harvested. Their high fat content, upwards of 20% as they approach spawning, also makes them vulnerable to the off-flavors of easily oxidized polyunsaturated fats. Thanks to this fragility most of these fish are preserved by smoking, salting, or canning.

Carp and Catfish

The freshwater carp family arose in east Europe and west Asia, and is now the largest family of fish on the planet. Some of the same characteristics that have made them so successful — the ability to tolerate stagnant water, low oxygen levels, and temperatures from just above freezing to 100ºF/38°C — have also made them ideal candidates for aquaculture, which China pioneered three millennia ago. Carp themselves can reach 60 lb/30 kg or more, but are generally harvested between one and three years when they weigh a few pounds. They’re relatively bony fish, with a coarse texture and a low to moderate fat content.

The mostly freshwater catfish family is also well adapted to an omnivorous life in stagnant waters, and therefore to the fish farm. Its most familiar member is the North American channel catfish (Ictalurus), which is harvested when about 1 ft/30 cm long and 1 lb/450 gm, but can reach 4 ft/1.2 m in the wild. Catfish have the advantage over the carps of a simpler skeleton that makes it easy to produce boneless fillets; they keep well, as much as three weeks when vacuum-packed on ice. Both carp and catfish can suffer from a muddy flavor (p. 193), particularly in the heat of late summer and fall.

Salmons, Trouts, and Relatives

The salmons and trouts are among the most familiar of our food fishes — and among the most remarkable. The family is one of the oldest among the fishes, going back more than 100 million years. The salmons are carnivores that are born in freshwater, go to the sea to mature, and return to their home streams to spawn. The freshwater trouts evolved from several landlocked groups of Atlantic and Pacific salmon.

Salmons Salmon develop their muscle mass and fat stores in order to fuel their egg production and nonstop upstream migration, processes that consume nearly half of their weight and leave their flesh mushy and pale. Salmon quality is thus at its peak as the fish approach the mouth of their home river, which is where commercial fishermen take them. The stocks of Atlantic salmon have been depleted by centuries of overfishing and damage to their home rivers, so nowadays most market fish come from farms in Scandinavia and North and South America. The wild Alaska fishery is still healthy. Opinions vary on the relative qualities of wild and farmed salmon. Some professional cooks prefer the fattiness and more consistent quality of farm fish, while others prefer the stronger flavor and firmer texture of wild fish at their best.

Salmons and Their Characteristics

Fat Content, %

Atlantic

Atlantic: Salmo salar

14

Pacific

King, Chinook: Oncorhynchus tshawytscha

12

Sockeye, Red: O. nerka

10

Coho, Silver: O. kisutch

7

Chum, Dog: O. keta

4

Pink: O. gorbuscha

4

Cherry, Amago (Japan and Korea): O. masou

7

size, lb/kg

Atlantic

Atlantic: Salmo salar

100/45; 6–12/3–5 farmed

Pacific

King, Chinook: Oncorhynchus tshawytscha

30+/14

Sockeye, Red: O. nerka

8/4

Coho, Silver: O. kisutch

30/14

Chum, Dog: O. keta

10–12/4–5

Pink: O. gorbuscha

5–10/2–4

Cherry, Amago (Japan and Korea): O. masou

4–6/2–3

Major Uses

Atlantic

Atlantic: Salmo salar

Fresh, smoked

Pacific

King, Chinook: Oncorhynchus tshawytscha

Fresh, smoked

Sockeye, Red: O. nerka

Fresh, canned

Coho, Silver: O. kisutch

Fresh, canned

Chum, Dog: O. keta

Roe, pet food

Pink: O. gorbuscha

Canned

Cherry, Amago (Japan and Korea): O. masou

Fresh

The Atlantic and the Pacific king salmons are well supplied with moistening fat, and yet don’t develop the strong flavor that similarly fatty herring and mackerel do. The distinctive salmon aroma may be due in part to the stores of pink astaxanthin pigment, which the fish accumulate from ocean crustaceans (p. 194), and which when heated gives rise to volatile molecules found in and reminiscent of fruits and flowers.

Trouts and Chars These mainly freshwater offshoots of the salmons are excellent sport fish and so have been transplanted from their home waters to lakes and streams all over the world. Their flesh lacks the salmon coloration because their diet doesn’t include the pigmented ocean crustaceans. Today, the trout found in U.S. markets and restaurants are almost all farmed rainbows. On a diet of fish and animal meal and vitamins, rainbow trout take just a year from egg to mild, single-portion (0.5–1 lb/225–450 gm) fish. The Norwegians and Japanese raise exactly the same species in saltwater to produce a farmed version of the steelhead trout, which can reach 50 lb/23 kg, and has the pink-red flesh and flavor of a small Atlantic salmon. Arctic char, which can grow to 30 lb/14 kg as migratory fish, are farmed in Iceland, Canada, and elsewhere to about 4 lb/2 kg, and can be as fatty as salmon.

The Cod Family

Along with the herring and tuna families, the cod family has been one of the most important fisheries in history. Cod, haddock, hake, whiting, pollack, and pollock are medium-sized predators that stay close to the ocean bottom along the continental shelves, where they swim relatively little — and thus have relatively inactive enzyme systems and stable flavor and texture. Cod set the European standard for white fish, with its mild flavor and bright, firm, large-flaked flesh, nearly free of both red muscle and fat.

Members of the cod family mature in two to six years, and once provided about a third the tonnage of the herring-family catch. Many populations have been exhausted by intensive fishing; but the northern Pacific pollock fishery is still highly productive (it’s used mostly in such prepared foods as surimi and breaded or battered frozen fish). Some cod are farmed in Norway in offshore pens.

Nile Perch and Tilapia

The mainly freshwater family of true perches are fairly minor foodfish in both Europe and North America. More prominent today are several farmed relatives that provide alternatives to scarce cod and flatfish fillets. The Nile or Lake Victoria perch can grow to 300 lb/135 kg on a diet of other fish, and is farmed in many regions of the world. The herbivorous tilapia is also a widely farmed native of Africa; it’s hardy and grows well at 60–90ºF/20–35ºC in both fresh and brackish water. A number of different species and hybrids are sold under the name tilapia, and have different qualities. Oreochromis nilotica is said to have been cultured the longest and to have the best flesh. The Nile perch and tilapia are among the few freshwater fish to produce TMAO, which breaks down into fishy-smelling TMA (p. 193).

Basses

The freshwater basses and sunfish of North America are mostly sport fish, but one has become an important product of aquaculture: the hybrid striped bass, a cross between the freshwater white bass of the eastern United States and the seagoing striped bass. The hybrid grows faster than either parent, is more robust, and yields more meat, which can remain edible for up to two weeks. Compared to the wild striped bass, the hybrid has a more fragile texture and bland flavor. Occasionally muddy aroma can be reduced by removing the skin.

The ocean basses — the American striped bass and European sea bass (French loup de mer, Italian branzino) are prized for their firm, fine-flavored flesh and simple skeletons; the sea bass is now farmed in the Mediterranean and Scandinavia.

Bass Family Relations

Sea Bass

European sea bass

Dicentrarchus labrax

Black sea bass

Centropristis striatus

Striped bass

Morone saxtalis

North American Freshwater Bass

White bass

Morone chrysops

Yellow bass

Morone mississippiensis

White perch

Morone americana

Hybrid striped bass

Morone saxtalis x Morone chrysops

Icefish

The “cod icefish” family is a group of large, sedentary plankton-eaters that live in the cold deep waters off Antarctica. The best known of them is the fatty “Chilean sea bass,” an inaccurate but more palatable commercial name for the Patagonian toothfish (Dissostichus eleginoides), which can reach 150 lb/70 kg. Its fat is located in a layer under the skin, in the chambered bones, and dispersed among the muscle fibers: toothfish flesh can be nearly 15% fat. It wasn’t until the mid-1980s that cooks came to know and appreciate this lusciously rich, large-flaked fish, which is unusually tolerant of overcooking. Like the orange roughy and other deepwater creatures, the toothfish is slow to reproduce, and there are already signs that its numbers have been dangerously depleted by overfishing.

Tunas and Mackerel

Who would know from looking at a cheap can of tuna that it was made from one of the most remarkable fish on earth? The tunas are large predators of the open ocean, reaching 1,500 lb/680 kg and swimming constantly at speeds up to 40 miles/70 km per hour. Even their fast-twitch muscle fibers, which are normally white and bland, contribute to the nonstop cruising, and have a high capacity for using oxygen, a high content of oxygen-storing myoglobin pigment, and active enzymes for generating energy from both fat and protein. This is why tuna flesh can look as dark red as beef, and has a similarly rich, savory flavor. The meaty aroma of cooked and canned tuna comes in part from a reaction between the sugar ribose and the sulfur-containing amino acid cysteine, probably from the myoglobin pigment, which produces an aroma compound that’s also typical of cooked beef.

Tuna has been the subject of connoisseurship at least since classical times. Pliny tells us that the Romans prized the fatty belly (the modern Italian ventresca) and neck the most, as do the Japanese today. Tuna belly, or toro, can have ten times the fat content of the back muscle on the same fish, and commands a large premium for its velvety texture. Because the bluefin and bigeye tunas live longest, grow largest, and prefer deep, cold waters, they accumulate more fat for fuel and insulation than other species, and their meat can fetch hundreds of dollars per pound.

These days, most tuna are harvested in the Pacific and Indian oceans. By far the largest catches are of skipjack and yellowfin tuna, small and medium-sized lean fish that reproduce rapidly and can be netted in schools near the surface. They also provide most of the world’s canned tuna, with the solitary light-fleshed albacore (Hawaiian tombo) giving “white” tuna. (Italian canned tuna is often made from the darker, stronger bluefin and from the dark portions of skipjack.)

Mackerels The mackerels are small relatives of the tunas. The mackerel proper is a native of the North Atlantic and Mediterranean, typically 18 inches/45cm long and 1–2 lb/0.5–1 kg. Like the tuna, it’s an energetic predator, with a large complement of red fibers, active enzymes, and an assertive flavor. It is usually netted in large numbers and sold whole, and deteriorates rapidly unless immediately and thoroughly iced.

Swordfish

The billfish are a family of large (to 13 ft/ 4 m and 2,000 lb/900 kg), active predators of the open oceans, with a spear-like projection from their upper jaw and dense, meaty, nearly boneless flesh that has been sought after for thousands of years. The preeminent billfish is the swordfish, whose Atlantic stock is thought to be down to less than a tenth of its original size and in need of protection. Swordfish have a dense, meaty texture and keep unusually well on ice, as long as three weeks.

Flatfish: Soles, Turbot,
Halibuts, Flounders

Flatfish are bottom-dwelling fish whose bodies have been compressed from the sides into a bottom-hugging shape. Most flatfish are relatively sedentary, and therefore are only modestly endowed with the enzyme systems that generate energy for the fish and flavor for us. Their mild flesh generally keeps well for several days after harvest.

The most prized flatfish is Dover or English sole, the principal member of a family found mainly in European waters (lesser U.S. flatfish are often misleadingly called sole). It has a fine-textured, succulent flesh said to be best two or three days after harvest, a trait that makes it an ideal fish for air-shipping to distant markets. The other eminent flatfish, the turbot, is a more active hunter. It can be double the size of the sole, with a firmer flesh that is said to be sweetest in a freshly killed fish. Thanks to their ability to absorb some oxygen through the skin, small turbot are farmed in Europe and shipped live in cold, moist containers to restaurants worldwide.

The halibut is the largest of the flatfish and a voracious hunter. The Atlantic and Pacific halibuts (both species of Hippoglossus) can reach 10 ft/3 m and 650 lb/300 kg, and their firm, lean flesh is said to retain good quality for a week or more. The distantly related “Greenland halibut” is softer and fattier, and the small “California halibut” is actually a flounder.

From the Waters
to the Kitchen

The quality of the fish we cook is largely determined by how it is harvested and handled by fishermen, wholesalers, and retail markets.

The Harvest

As we’ve seen, fish and shellfish are a more delicate and sensitive material than meat. They’re the animal equivalent of ripe fruit, and ideally they would be handled with corresponding care. The reality is otherwise. In a slaughterhouse it’s possible to kill each animal in a controlled way, minimize the physical stress and fear that adversely affect meat quality, and process the carcass immediately, before it begins to deteriorate. The fisherman has no such mastery over the circumstances of the catch, though the fish farmer has some.

Harvest from the Ocean There are several common ways of harvesting fish from the wild, none of them ideal. In the most controlled and least efficient method, a few fisherman catch a few fish, ice them immediately, and deliver them to shore within hours. This method can produce very fresh and high-quality fish — if they are caught quickly with minimal struggle, expertly killed and cleaned, quickly and thoroughly iced, and promptly delivered to market. But if the fish are exhausted, processing is less than ideal, or cold storage is interrupted, quality will suffer. Far more common are fish caught and processed by the thousands and delivered to port every few days or weeks. Their quality often suffers from physical damage caused by the sheer mass of the catch, delays in processing, and storage in less than ideal conditions. Factory-scale trawlers and longliners also harvest huge numbers of fish, but they do their own processing on board, and often clean, vacuum-pack, and freeze their catch within hours. Such fish can be superior in quality to unfrozen fish caught locally and recently but handled carelessly.

Harvest in Aquaculture By contrast to the logistical challenge posed by fishing, consider the care with which salmon are harvested in the best aquaculture operations. First, the fish are starved for seven to ten days to reduce the levels of bacteria and digestive enzymes in the gut that may otherwise accelerate spoilage. The fish are anesthetized in chilled water saturated with carbon dioxide, then killed either with a blow to the head or by bleeding with a cut through the blood vessels of the gill and tail. Because the blood contains both enzymes and reactive hemoglobin iron, bleeding improves the fish’s flavor, texture, color, and market life. Workers then clean the fish while it’s still cold, and may wrap it in plastic to protect it from direct contact with ice or air.

The Effects of Rigor Mortis and Time

We sometimes eat fish and shellfish very fresh indeed, just minutes or hours after their death, and before they pass through the chemical and physical changes of rigor mortis (p. 143). This stiffening of the muscles may begin immediately after death in a fish already depleted by struggling, or many hours later in a fat-farmed salmon. It “resolves” after a few hours or days when the muscle fibers begin to separate from each other and from the connective-tissue sheets. Fish and shellfish cooked and eaten before rigor has set in are therefore somewhat chewier than those that have passed through rigor. Some Japanese enjoy slices of raw fish that are so fresh that they’re still twitching (ikizukuri); Norwegians prize cod held in tanks at the market and killed to order just before cooking (blodfersk, or “blood-fresh”); Chinese restaurants often have tanks of live fish at the ready; the French prepare freshly killed “blue” trout; and many shellfish are cooked alive.

In general, delaying and extending the period of rigor will slow the eventual deterioration of texture and flavor. This can be done by icing most fish immediately after harvest, before rigor sets in. However, early icing can actually toughen some fish — sardine, mackerel, and warm-water fish such as tilapia — by disrupting their contraction control system. Fish are generally at their prime just when rigor has passed, perhaps 8 to 24 hours after death, and begin to deteriorate soon after that.

Recognizing Fresh Fish

Nowadays, consumers often have no idea where a given piece of fish in the market has come from, when and how it was harvested, how long it has been in transit, or how it has been handled. So it’s important to be able to recognize good-quality fish when we see it. But looks and smell can be deceiving. Even perfectly fresh fish may not be of the best quality if it has been caught in a depleted state after spawning. So the ideal solution is to find a knowledgeable and reliable fish merchant who knows the seasonality of fish quality, and buys accordingly. Such a merchant is also more likely to be selective about his suppliers, and less likely to sell seafood that’s past its prime.

It’s preferable to have fillets and steaks cut to order from a whole fish, because cutting immediately exposes new surfaces to microbes and the air. Old cut surfaces will be stale and smelly.

In the case of a whole fish:

• The skin should be glossy and taut. On less fresh fish it will be dull and wrinkled. Color is not a helpful guide because many skin colors fade quickly after the fish dies.
• If present, the natural proteinaceous mucus covering the skin should be transparent and glossy. With time it dries out and dulls, the proteins coagulate to give a milky appearance, and the color goes from off-white to yellow to brown. The mucus is often washed off when the fish is cleaned.
• The eyes should be bright, black, and convex. With time the transparent surface becomes opaque and gray and the orb flattens out.
• The belly of an intact fish should not be swollen or soft or broken, all signs that digestive enzymes and bacteria have eaten through the gut into the abdominal cavity and muscle. In a dressed fish, all traces of the viscera should have been removed, including the long red kidney that runs along the backbone.

If the fish has already been cut up, then:

• The steaks and fillets should have a full, glossy appearance. With time, the surfaces dry out and the proteins coagulate into a dull film. There should be no brown edges, which are a sign of drying, oxidation of oils, and off-flavors.
• Whether the fish is precut or whole, its odor should resemble fresh sea air or crushed green leaves, and be only slightly fishy. Strong fishiness comes from prolonged bacterial activity. More advanced age and spoilage are indicated by musty, stale, fruity, sulfurous, or rotten odors.

Storing Fresh Fish and Shellfish: Refrigeration and Freezing

Once we’ve obtained good fish, the challenge is to keep it in good condition until we use it. The initial stages of inevitable deterioration are caused by fish enzymes and oxygen, which conspire to dull colors, turn flavor stale and flat, and soften the texture. They don’t really make the fish inedible. That change is caused by microbes, especially bacteria, with which fish slime and gills come well stocked — particularly Pseudomonas and its cold-tolerant ilk. They make fish inedible in a fraction of the time they take to spoil beef or pork, by consuming the savory free amino acids and then proteins and turning them into obnoxious nitrogen-containing substances (ammonia, trimethylamine, indole, skatole, putrescine, cadaverine) and sulfur compounds (hydrogen sulfide, skunky methanethiol).

The first defense against incipient spoilage is rinsing. Bacteria live and do their damage on the fish surface, and thorough washing can remove most of them and their smelly by-products. Once the fish is washed and blotted dry, a close wrapping in wax paper or plastic film will limit exposure to oxygen.

But by far the most important defense against spoilage is temperature control. The colder the fish, the slower enzymes and bacteria do their damage.

Refrigeration: The Importance of Ice For most of the foods that we want to store fresh for a few days, the ordinary refrigerator is quite adequate. The exception to the rule is fresh fish, whose enzymes and microbes are accustomed to cold waters (p. 189). The key to maintaining the quality of fresh fish is ice. Fish lasts nearly twice as long in a 32ºF/0ºC slush as it does at typical refrigerator temperatures of 40–45ºF/5–7ºC. It’s desirable to keep fish on ice as continuously as possible: in the market display case, the shopping cart, the car, and in the refrigerator. Fine flake or chopped ice will make more even contact than larger cubes or slabs. Wrapping will prevent direct contact with water that leaches away flavor.

In general, well iced fatty saltwater fish — salmon, herring, mackerel, sardine — will remain edible for about a week, lean cold-water fish — cod, sole, tuna, trout — about two weeks, and lean warm-water fish — snappers, catfish, carp, tilapia, mullets — about three weeks. A large portion of these ice-lives may already have elapsed before the fish appear in the market.

Freezing To keep fish in edible condition for more than a few days, it’s necessary to lower its temperature below the freezing point. This effectively stops spoilage by bacteria, but it doesn’t stop chemical changes in the fish tissues that produce stale flavors. And the proteins in fish muscle (especially cod and its relatives) turn out to be unusually susceptible to “freeze denaturation,” in which the loss of their normal environment of liquid water breaks some of the bonds holding the proteins in their intricately folded structure. The unfolded proteins are then free to bond to each other. The result is tough, spongy network that can’t hold onto its moisture when it’s cooked, and in the mouth becomes a dry, fibrous wad of protein.

So once you’ve brought frozen fish home, it’s best to use it as soon as possible. In general, the storage life of fish in ordinary freezers, wrapped tightly and/or glazed with water to prevent freezer burn (freeze the fish, then dip in water, refreeze, and repeat to build up a protective ice layer) is about four months for fatty fish such as salmon, six months for most lean white fish and shrimp. Like frozen meats, frozen fish should be thawed in the refrigerator or in a bath of ice water (p. 147).

Irradiation

Irradiation preserves food by way of high-energy particles that damage the DNA and proteins of spoilage microbes (p. 782). Pilot studies have found that irradiation can extend the refrigerated shelf life of fresh fish by as much as two weeks. However, the initial deterioration of fish quality is caused by the action of fish enzymes and oxygen, and this action proceeds despite irradiation. Also, irradiation can produce off-flavors of its own. It’s unclear whether irradiation will become an important means of preservation for fish.

Unheated Preparations
of Fish and Shellfish

People in many parts of the world enjoy eating ocean fish and shellfish raw. Unlike meats, fish have the advantage of relatively tender muscle and a naturally savory taste, and are easier and more interesting to eat raw. They offer the experience of a kind of primal freshness. The cook may simply provide a few accompanying ingredients with complementary flavors and textures, or firm the fish’s texture by means of light acidification (ceviche), salting (poke), or both (anchovies briefly cured in salt and lemon juice). And raw preparations don’t require the use of fuel, which is often scarce on islands and coastlines.

All uncooked fresh fish pose the risk of carrying a number of microbes and parasites that can cause food poisoning or infection (p. 185). Only very fresh fish of the highest quality should be prepared for consumption raw, and they should be handled very carefully in the kitchen to avoid contamination by other foods. Because parasitic worms are often found in otherwise high-quality fish, the U.S. Food Code specifies that fish sold for raw consumption should be frozen throughout for a minimum of 15 hours at –31ºF/–35ºC, or for seven days at –4ºF/–20ºC. The exceptions to this rule are the tuna species commonly served in Japanese sushi and sashimi (bluefin, yellowfin, bigeye, albacore), which are rarely infected with parasites. Despite this exception, most tuna are blast-frozen at sea so that the boats can stay out for several days at a time. Sushi connoisseurs say that the texture of properly frozen tuna is acceptable, but that the flavor suffers.

Sushi and Sashimi

Probably the commonest form of raw fish is sushi, whose popularity spread remarkably in the late 20th century from its home in Japan. The original sushi seems to have been the fermented preparation narezushi (p. 235); sushi means “salted” and now applies more to the flavored rice, not the fish. The familiar bite-sized morsels of raw fish and lightly salted and acidified rice are nigiri sushi, meaning “grasped” or “squeezed,” since the rice portion is usually molded by hand. The mass-produced version of sushi found in supermarkets is formed by industrial robots.

Sushi chefs take great care to avoid contamination of the fish. They use a solution of cold water and chlorine bleach to clean surfaces between preparations, and they change cleaning solutions and cloths frequently during service.

Tart Ceviche and Kinilaw

Ceviche is an ancient dish from the northern coast of South America, in which small cubes or thin slices of raw fish are “cooked” by immersing them in citrus juice or another acidic liquid, usually with onion, chilli peppers, and other seasonings. This period of marination changes both the appearance and texture of the fish: in a thin surface layer if it lasts 15–45 minutes, throughout if it lasts a few hours. The high acidity denatures and coagulates the proteins in the muscle tissue, so that the gel-like translucent tissue becomes opaque and firm: but more delicately than it does when heated, and with none of the flavor changes caused by high temperatures.

Kinilaw is the indigenous Philippine version of acid marination. Morsels of fish or shellfish are dipped for only a few seconds into an acidic liquid, often vinegar made from the coconut, nipa palm, or sugarcane, to which condiments have been added. In the case of “jumping salad,” tiny shrimp or crabs are sprinkled with salt, doused with lime juice, and eaten alive and moving.

Salty Poke and Lomi

To the world’s repertoire of raw fish dishes, the Hawaiian islands have contributed poke (“slice,” “cut”) and lomi (“rub,” “press,” “squeeze”). These are small pieces of tuna, marlin, and other fish, coated with salt for varying periods (until the fish stiffens, if it’s to be kept for some time), and mixed with other flavorful ingredients, traditionally seaweed and roasted candlenuts. Lomi is unusual in that the piece of fish is first worked between the thumb and fingers before salting, to break some of the muscle sheets and fibers apart from each other and soften the texture.

Cooking Fish and Shellfish

The muscle tissues of fish and shellfish react to heat much as beef and pork do, becoming opaque, firm, and more flavorful. However, fish and shellfish are distinctive in a few important ways, above all in the delicacy and activity of their proteins. They therefore pose some special challenges to the cook who wants to obtain a tender, succulent texture. Shellfish in turn have some special qualities of their own; they’re described beginning on p. 218.

If it’s more important to produce the safest possible dish than the most delicious one, then the task is simpler: cook all fish and shellfish to an internal temperature between 185ºF/83ºC and the boil. This will kill both bacteria and viruses.

How Heat Transforms
Raw Fish

Heat and Fish Flavor The mild flavor of raw fish gets stronger and more complex as its temperature rises during cooking. At first, moderate heat speeds the activity of muscle enzymes, which generate more amino acids and reinforce the sweet-savory taste, and the volatile aroma compounds already present become more volatile and more noticeable. As the fish cooks through, its taste becomes somewhat muted as amino acids and IMP combine with other molecules, while the aroma grows yet stronger and more complex as fatty-acid fragments, oxygen, amino acids, and other substances react with each other to produce a host of new volatile molecules. If the surface temperature exceeds the boiling point, as it does during grilling and frying, the Maillard reactions produce typical roasted, browned aromas (p. 778).

Shellfish have their own distinctive cooked flavors (pp. 221, 225). Cooked fish fall into four broad flavor families.

• Saltwater white fish are the mildest.
• Freshwater white fish have a stronger aroma thanks to their larger repertoire of fatty-acid fragments and traces of earthiness from ponds and tanks. Freshwater trout have characteristic sweet and mushroomy aromas.
• Salmon and sea-run trout, thanks to the carotenoid pigments that they accumulate from ocean crustaceans, develop fruity, flowery aromas and a distinctive family note (from an oxygen-containing carbon ring).
• Tuna, mackerel, and their relatives have a meaty, beefy aroma.

Fishiness and How to Fight It The house-permeating “fishy” aroma of cooked fish appears to involve a group of volatile molecules formed by fatty-acid fragments reacting with TMAO (p. 193). Japanese scientists have found that certain ingredients help reduce the odor, apparently by limiting fatty-acid oxidation or preemptively reacting with TMAO: these include green tea and such aromatics as onion, bay, sage, clove, ginger, and cinnamon, which may also mask the fishy smell with their own. Acidity — whether in a poaching liquid, or in a buttermilk dip before frying — also mutes the volatility of fishy amines and aldehydes, and helps break down muddy-smelling geosmin that farmed freshwater fish (catfish, carp) sometimes accumulate from blue-green algae.

Simple physical treatments can also minimize fishy odors. Start with very fresh fish and wash it well to remove oxidized fats and bacteria-generated amines from the surface. Enclose the fish in a covered pan, or pastry crust, or parchment or foil envelope, or poaching liquid, to reduce the exposure of its surface to the air; frying, broiling, and baking all propel fishy vapors into the kitchen. And let the fish cool down to some extent before removing it from its enclosure; this will reduce the volatility of the vapors that do escape.

Heat and Fish Texture The real challenge in cooking both fish and meat is to get the texture right. And the key to fish and meat texture is the transformation of muscle proteins (p. 149). The cook’s challenge is to control the process of coagulation so that it doesn’t proceed too far, to the point that the muscle fibers become hard and the juice flow dries up completely.

Target Temperatures In meat cooking, the critical temperature is 140ºF/60ºC, when the connective-tissue collagen sheath around each muscle cell collapses, shrinks, and puts the squeeze on the fluid-filled insides, forcing juice out of the meat. But fish collagen doesn’t play the same critical role, because its squeezing power is relatively weak and it collapses before coagulation and fluid flow are well underway. Instead, it’s mainly the fiber protein myosin and its coagulation that determine fish texture. Fish myosin and its fellow fiber proteins are more sensitive to heat than their land-animal counterparts. Where meats begin to shrink from coagulation and major fluid loss at 140ºF/60ºC and are dry by 160ºF/70ºC, most fish shrink at 120ºF/50ºC and begin to become dry around 140ºF/60ºC. (Compare the behaviors of meat and fish proteins in the boxes on pp. 152 and 210).

In general, fish and shellfish are firm but still moist when cooked to 130–140ºF/55–60ºC. Some dense-fleshed fish, including tuna and salmon, are especially succulent at 120ºF, when still slightly translucent and jelly-like. Creatures with a large proportion of connective-tissue collagen — notably the cartilagenous sharks and skates — benefit from higher temperatures and longer cooking to turn it into gelatin, and can be chewy unless cooked to 140ºF/60ºC or higher. Some molluscs are also rich in collagen and benefit from long cooking (p. 225).