Fish & Shellfish Identification

Fish Composition

Fish is composed of 70-80% water, 15-20% proteins, 1-13% fat, and 1% minerals. Fat, also known as lipids, contains important omega-3 fatty acids that provide health benefits by helping to lower cholesterol and blood pressure. Generally speaking, fish have an easier life in the water than land animals so their muscles don’t work as hard. This results in a naturally tender product that requires minimal cooking.

The proteins in fish are different from meats because rather than bundles of muscle wrapped in connective tissue they are instead layered with collagen creating a “W” or wave-like appearance that creates a flaking effect when cooked. Fish collagen is layered between the folds of the muscle tissues and is weaker than animal connective tissue. This means that fish do not have to cook for long periods of time to make them palatable.  Fish collagen melts into gelatin at about 120˚F/60˚C. The fat content can vary greatly in during growth, spawning, or migration periods. Fish that are in colder waters tend to be fattier than warm water fish. Whether a fish is lean or fatty determines the perceived moistness on the palate. Fat content also dictates cooking methods.

Some fish contain a dark blood-rich muscle running down the center of the fillet called the “bloodline” (which actually contains no blood). The bloodline is a good indicator of freshness, which is bright pink or red when fresh but turns brown as the fish ages. The dark region contains high levels of myoglobin, the same chemical responsible for the red color of meats, and has a strong, fishy taste which is why it is usually removed.

Skeletal Structure

Round Fish Skeleton

For most fish the skeleton is made of bone, but some varieties, including shark, skate, and ray, are made of cartilage. The skeletal structure, along with the size of the fish, determines how fish are filleted.

Flat Fish Skeleton

Flat Fish Skeleton

Shark Skeleton

Fish Identification

The sheer variety of fish makes purchasing, fabricating, and cooking fish more of a challenge than working with meats and poultry. Adding to the challenge is a common problem of mislabeled fish that creates opportunities of economic fraud on uninformed buyers (only 2% of all imported fish is inspected by the FDA). Purchasing fish from a reputable supplier will help to prevent this type of fraud.

Fish are generally divided into different categories depending on their family and species, whether they are fresh or saltwater fish, by their body shape (if they are round, flat, or cartilaginous fish), by fat content, whether they are fatty or lean fish, and if they are cold- or warm-water fish.

Families are large groups of fish, for example salmon, and the species include the Atlantic, King, or Coho varieties. The salmon family also includes trout and char.
There are differences in flavor between salt water and freshwater fish. Saltwater fish, because of the salinity of their environment, produce sweet-tasting glycine and savory glutamate amino acids that milder-tasting freshwater fish lack.

Round fish are symmetrical with identical coloring on both sides, while flat fish swim sideways, have asymmetrical eyes (eyes on one side of the head), and are darkly pigmented on their top side while white on the bottom. Cartilaginous fish includes shark, skate, and ray, containing no ossified bones.

Fat content determines the best method for cooking fish. Lean fish that have almost no fat content become dry when overcooked, while fattier fish are able to tolerate more heat without drying too quickly.

Warm-water fish are found along the Gulf Stream, reefs, and warm seas like the Mediterranean. Cold-water fish are from the deep waters or colder areas of the oceans and have characteristics that include firm flesh and higher levels of fat.

Fish categories in this section are grouped according to their families, and in some cases paired with varieties from other families that possess a similar structure, texture, and fat content, or if they are fabricated and cooked in like ways.

Anchovy and Herring

Anchovy and herring are oily fish high in omega-3 of the Engraulidae family, and although found fresh in European countries, they are often salted, smoked, or pickled.



Salmon, Trout, Char, and Whitefish

Salmon, are found wild in northern oceans, while trout and char are found in freshwater lakes and streams. These varieties of the Salmonidae family are also extensively farmed. They are relatively fatty making them versatile for a variety of cooking methods including grilling, broiling, sautéing, and roasting, and are also served raw, cured, or smoked. Freshwater Lake Whitefish, also a member of the salmon family found throughout Canada and the Great Lakes region of the United States, is a delicate lean fish with a mild flavor that can be cooked similar to trout and char.


Rainbow Trout

Lake Whitefish

Tuna, Swordfish, Mackerel

Tuna, swordfish, and mackerel are members of the Scombridae family, and while marlin is a relative of this family, swordfish is the sole member of the Xiphiidae family. These large predatory fish are found throughout the globe in temperate to tropical waters of the Atlantic, Pacific, and Indian oceans. Tuna, the most significant of this species includes Atlantic, Pacific, and southern Bluefin varieties prized for sushi and sashimi, while Albacore is the most common canned variety.  These fish are rich, oily, and have a meaty flavor suitable for grilling and broiling.





The Cod family, including Haddock and Pollack, are found in northern ocean waters including New England, Alaska, Canada, Asia, and Europe. For centuries dating back to the era of the Vikings, cod has been one of the most commercially important fish that was processed by salting and drying and later became part of the tringle trade to the Caribbean. Cod is also used extensively in processed frozen foods too. Today because of pressure on cod populations from overfishing in New England and North Sea fisheries, the amount of catch is severely limited. Haddock, Pollack, and Hake are similar in texture and have been used as substitutes for cod. These fish are delicate white-fleshed fish that versatile for cooking by a variety of methods and are particularly suitable for deep-frying, broiling, poaching, baking, and roasting.

Atlantic Cod


Perch Family

The Perciform fish family includes freshwater varieties found in Europe, Asia, and North America. The yellow perch is native to the Great Lakes Region. Zander is native to Eurasia and also known as pikeperch. Tilapia, also known as St. Peter’s Fish, is a freshwater species related to perch found in the Middle East and Africa. Today, tilapia is the third most important farmed fish, after carp and salmon, in countries including China, the Philippines, Taiwan, Indonesia and Thailand. Perch varieties including tilapia are known for their firm yet tender meat and delicate flavor suitable for frying, sautéing, broiling, baking, and poaching.

Yellow Perch

Zander (Pikeperch)





A name shared with over 475 species, the Bass family, actually a Perch species, includes varieties located around the world. Atlantic Striped Bass are found along the coasts from Canada to Florida. White Sea Bass is found along the California coast.  Grouper varieties including red, black, and gag are found from the mid-Atlantic States down through the Gulf of Mexico and along both coasts of South America. European Seabass are found extensively throughout Europe especially around the Mediterranean Sea. Barrimundi is found from the Persian Gulf, through Southeast Asian, and down to Australia. Many varieties of bass are farm raised today. Chilean Sea Bass, also known as Patagonian Toothfish is found in water near Antarctica and is unrelated to the bass family. Bass are versatile fish, firm yet delicate flesh, medium-flavored, and are suitable for almost any cooking method from grilling, to sautéing, and poaching.

Atlantic Striped Bass


White Bass

White Bass


Patagonian Toothfish (Chilean Sea Bass)

Black Bass


From the family of Perciforms, there are over 100 varieties of snapper found in abundance throughout the tropics. These fish share similar characteristics with bass and other perch varieties.  Their meat is light colored, firm yet tender flesh, mild flavor, make them suitable for most cooking methods including grilling, sautéing, grilling, poaching, and roasting.

Red Snapper

Rockfish (Pacific Ocean Perch)

Rockfish (Pacific Ocean Perch)


Flatfish including halibut, sole, and turbot are Pleuronectiformes that swim sideways and possess asymmetrical eyes on one side of their head. The skin, dark on the upper side and white on the underside, is thought to act as camouflage. Flatfish are found in oceans around the world from the artic, to the tropics, and down to Antarctica. Some varieties, including halibut and turbot, are also farmed today.
Halibut are the largest of the flatfish weighing as much as 150 lb./70 kg and are found in the Pacific, North Atlantic, and the North Sea. Turbot average about 10-20 lb./4-9 kg and are found in the Mediterranean, the Baltic Sea, the Black Sea, and the North Atlantic. Flounder are found in the Atlantic off the coast of Canada, the United States, and the Gulf of Mexico with a weight range of 4-8 lb./1.8-3.6 kg, while European varieties are harvested from the Mediterranean Sea averaging about 1.5 lb./680g to. Dover sole, considered a highly prized fish, are found off the eastern Atlantic Ocean, the Baltic and Mediterranean Seas and average 24-28 oz./700-800 g.
Flatfish are white fleshed and lean, with a mild, sweet taste and a large flake. Poaching, steaming, sautéing, and pan-frying are the best methods. The fillets can easily overcook and become dry so special attention to cooking is required.





Dover Sole

Catfish, Orange Roughy, Mahi Mahi, Monkfish


Although catfish are caught wild, they are widely farmed in Africa, Asia, Europe, and in North America, especially throughout the Mississippi River Delta. Catfish are bottom feeders traditionally known for their muddy taste, however today’s farming techniques have developed lighter tasting flavors that are mild and sweet with a frim texture suitable for frying, sautéing, grilling, broiling, and baking.

Orange Roughy are members of the slimehead family found in deep waters mainly around New Zealand, but also near southern Africa, the northeast Atlantic, the South Indian Ocean, and off the coast of Chile. The fish’s skin is a bright red color that fades to red-orange after harvesting. The skin and bloodline is removed from the fillets because the fish oils produce off-tasting flavors. The milky white fish is delicate and mild tasting, with a large flake. Because the fish are slow maturing, taking 25-50 years to mature to market size of 3-4 lb./1.4-1.8 kg, they have experienced over fishing and a collapse in population. Tilapia is recommended as a substitute for this fish.

Orange Roughy

Orange Roughy are members of the slimehead family found in deep waters mainly around New Zealand, but also near southern Africa, the northeast Atlantic, the South Indian Ocean, and off the coast of Chile. The fish’s skin is a bright red color that fades to red-orange after harvesting. The skin and bloodline is removed from the fillets because the fish oils produce off-tasting flavors. The milky white fish is delicate and mild tasting, with a large flake. Because the fish are slow maturing, taking 25-50 years to mature to market size of 3-4 lb./1.4-1.8 kg, they have experienced over fishing and a collapse in population. Tilapia is recommended as a substitute for this fish.

Mahi Mahi

Mahi Mahi, also known as Dorado in the Caribbean and South America, and Dolphinfish (however it is not related to dolphins which are mammals), is a lean firm fish with a sweet and mild to moderate flavor similar to swordfish. The fish is found in tropical waters around the world, and is the only known member of the Coryphaena family. It can be handled in in similar methods as snapper and bass. The flesh gray and pink when raw but white when cooked is firm and sweet prepared by sautéing, frying, broiling and grilling, and baking or roasting


Monkfish inhabit the northern Atlantic coasts of North America and Europe, the Mediterranean Sea, and the coasts of China and Japan. They live as long as 24 years, and mature between 9-11 years with females weighing as much as 88 lb./40 kg while males are about half that size.  Monkfish possess a large, broad, flat head that is about 75% of the weight of the fish. They are also known as poor man’s lobster, due to the texture and taste of the meat. The fish should be trimmed of the bloodline and connective tissue surrounding the fillets before cooking. Monkfish are prepared by pan-frying, sautéing, roasting, broiling, poaching, and stewing.

Shark, Skate, Ray

Shark, skate, and ray are chondrichthyans with cartilaginous skeletons that have no ribs or bone marrow.  The skin of these fish are tough with tooth-like scales. Sharks are found around the globe with many species facing over fishing because they are slow growing, some living for as long as 200 years. The demand for shark fin soup, a Chinese delicacy, has created controversy because only the fins are harvested from the fish and the rest is thrown back into the water to die. Many have called for a boycott of this practice and a moratorium on shark fishing. Skate and ray are kite-shaped fish related to sharks that are native to the Atlantic, Pacific, and Indian Oceans and can be found in tropical to cold climates. Market sizes for these fish are about 10 lb./4.5 kg. The wings are the edible portion with cartilage found between the top and bottom fillets. The mild, sweet fish is sautéed, poached, or roasted.






Shellfish Composition

Shellfish is generally composed of 75-80% water, 15-20% protein, 2-5% fat, 1-2% minerals. The meat of crustaceans including lobster, shrimp, and crab is white fleshed, with connective tissue that has more collagen and is therefore not as tender as fish.  Mollusks, including abalone have a muscular foot that helps them move around, while clams and oysters have an adductor muscle to open and close their shells. Squid and octopus are mollusks turned inside out that have tough-collagen rich muscles.

Skeletal Structure

Divers Scallops.jpg

Crustaceans including lobster, shrimp, and crab have exoskeletons with hard outer shells protecting their bodies. They have segmented bodies that protect their muscles and organs giving them structural support, and periodically shed their shells through molting as they grow larger. Mollusks have hard shells that protect them from predators composed of a chalky material called calcium carbonate.

Shellfish Identification

Shellfish are divided into two general categories that include crustaceans and mollusks Crustaceans are arthropods, related to the insect family, and easily identified by their hard, segmented bodies. Mollusks are divided into gastropods with a single shell like snails; bivalves with hinged shells like clams; and cephalopods like octopus are without shells. Echinoderms represent a small class of shellfish that includes the spiny sea urchin with hard shells and long spines that are very sharp and protect them from predators.


Crustaceans include lobster, shrimp, crab, and fresh-water varieties including crawfish. Shrimp and lobster meat is most abundant in the tail with the exception of the American lobster which has large claws and a fair amount of meat. Crabs have a shorter body and because they don’t move around much the muscles in their tentacles and claws make up most of the edible meat. Soft shell crabs are molting crabs and are prepared and consumed whole. Unless held live, crustaceans will deteriorate quickly because the mid-gut glands, liver and intestines, will break down and turn the muscles into mush. Most crabs are pre-cooked because of this rapid deterioration, while lobster and shrimp tails are commonly separated and frozen in their raw state. Crustaceans are a dark green-to-blue color that blends in with their environment, but when cooked turn a bright orange or red color from carotenoid pigments caused by the plankton in their diet.


Shrimp are swimming crustaceans that can range in size from less than 1 in./3 cm to about 10 in./25 cm in length. There are about 300 edible varieties of saltwater and freshwater shrimp. The term prawn is the term commonly used in Great Britain for shrimp but in the United States a prawn can refer to a large shrimp. Dublin Bay Prawns are actually langoustine, related to lobsters.


Lobsters are crawling crustaceans that live on the ocean floor. They are divided into several species for commercial purposes. The American lobster, found along the eastern seaboard of the United States and Canada, is notable for its claws. It takes 6-7 years for a lobster to reach edible size of 1-2 Lb. /450-900 g. Spiny or Rock Lobsters are found in warmer waters including the Caribbean, Mediterranean, Australia, Asia, and South Africa. They have large tails and long spiny antenna but lack the large claws of the American Lobster. In Australia, New Zealand, and South Africa they are known as crayfish. Langoustine, sometimes called Dublin Bay Prawns, Norway Lobster, or Scampi, are found in the north-eastern Atlantic Ocean and North Sea as far north as Iceland and northern Norway, and south to Portugal and also in parts of the Mediterranean Sea. They can grow to 7–8 in. /18–20 cm.

Lobster tails are sold as either warm-water lobster varieties originating from California, Florida, the Mediterranean, South Pacific, Caribbean, New Guinea, New Zealand, Australia and South Africa, or cold-water lobsters mainly from from the north Atlantic and off the coast of New Zealand, Australia and South Africa. Cold water varieties tend to be firmer, more tender meat, and sweeter tasting than warm-water tails which can be softer in texture. Caribbean warm-water tails have distinct yellow spots and a yellow band across the tail. Maine Lobster Tails, of the American Lobster variety have whiter meat and are considered more tender because they grown more slowly in colder winters.


Unlike shrimp and lobster which are prized for their tails, crabs have small bodies but long legs and claws where most of the edible meat is concentrated. Crabs vary from very small to quite large in size and weight.  Although live crabs are purchased and consumed fresh near the coasts, most crab meat is cooked, processed, and sold as fresh pasteurized or frozen.

King Crab, prized for their leg meat, are the largest species of edible crab weighing in at 10-15 lbs. /4.5-6.8 K with a leg span of 5 ft. /1.5m. They are found in the northern oceans off the coasts of Alaska, Canada, Russia and Japan, and in the southern hemisphere near Australia, Chile and Argentina.  There are three commercially marketed species, golden, blue and red that are found in the waters of Alaska with red king crab considered the best quality.

Snow Crabs are found in the northern Pacific and Atlantic Oceans including the Bering Strait in Alaska, Sea of Japan, Newfoundland, and Norway. They measure 6-6 in./9.5-15 cm and weigh up to 3 lbs. /1.3 kg. They are usually sold cooked and frozen as legs and claws.

Dungeness Crabs are harvested from the west coast of North America from Washington to California. They grow to about 8 inches / 20 cm, weigh from 1.5 to 3 Lb. /0.7-1.3 K and typically have a yield of 25% useable meat.The Jonah Crab, found on the Atlantic coast of North America is related to the west coast Dungeness crab. They are harvested at about 7 inches /18 cm in length. Jonah crab meat is more uniformly white and the large claws have more meat than the legs.

Blue Crabs are found along the east coast of North America from Nova Scotia to the Gulf of Mexico, through the Caribbean Sea, and down the east coast of South America. An average size fresh blue crab weighs about a third of a pound. The yield from a pound of fresh blue crab is about 14% which equates to about 2.25 oz./68 g per pound /450 g of whole shell-on crab. Blue crab is commonly cooked, cleaned, and pasteurized for purchase as lump, flake or claw meat. Lump crab meat is considered the most desirable because it is large whiter chunks from the body of the crab. Soft-Shell Crabs are molting blue crabs available in the spring months and are meant to be eaten whole.

Stone Crabs are found off the east coast of North America from Connecticut down to Belize, South America, and in the Gulf of Mexico. Commonly marketed as Florida Stone Crabs, they are about 5 to 6.5 inches /13-17 cm across. Because their bodies are small, yielding little meat, they are mostly prized for their claws. Harvesting is done by removing one or both of the claws from the live animal and returning them to the ocean where they can regrow their lost limbs.


Mollusks are divided into separate categories including gastropods (also known as univalves), bivalves, and cephalopods. Gastropods have a single shell and include snails (escargot), conch, and abalone. These mollusks, because of their connective tissue, can be very tough when cooked. They are often mechanically tenderized, sliced thin, and either cooked minimally, or stewed for several hours. Bivalves including oysters, mussels, clams, and scallops, have hinged shells that open and close helping them maneuver in the water. Clams and oysters are often served raw, while mussels are often gently steamed for a few minutes. Scallops are prized for their white adductor muscles that are quite tender when minimally cooked.


Clams are a bivalve mollusk found in various sizes around the world. There are over 2000 species of clams and about 150 edible clam varieties. Unlike mussels and oysters that attach themselves to rocks and reefs, clams bury themselves in sand or sediment.
Clam species are divided into hard-shell and soft-shell varieties. Soft shell clams live off the coasts in shallow waters and hard shell varieties live in deep waters and tend to be larger. Clams can vary in size from as small as 1.5 in. /4 cm for a soft shell steamer clam to as large as 8 in./ 20 cm for a hard shell Geoduck clam. Varieties that are farmed in North America included Soft-Shell Steamers, Littleneck, Cherrystone, Manila Razor, Quahog, and Geoduck.


Mussels are bivalve mollusks found around the world. The two most common species cultivated are the New Zealand Green-Lipped Mussel, and in Canada the Prince Edward Island Blue Mussel. Like most bivalves, mussels have a large organ called a foot connected to the byssus thread also known as the "beard" which is removed before the mussels are cooked. Modern farm raised mussel processing now removes the beard.


Oysters are a bivalve mollusk found globally usually in the beds and reefs of shallow waters and estuaries. Salinity, mineral, and nutrient variations in the water influences their flavor profile. They are able to reproduce on their own and will change their sex from male to female. The most common oysters include the Eastern American Oyster, on the eastern Atlantic coast from Canada to Argentina, and the Pacific Oyster, found off the shores of Japan to Washington State and as far south as Australia. The Pacific oyster is the most widely cultured in the world and includes the Kumamoto and the Olympia. North American varieties on the Atlantic coast include Malpeque, Cotuit, and the Blue Point. The Belon oyster, from the Brittany region of France, is a European Flat variety.


Scallops are marine bivalves found around the globe with most harvested off of the east coast of the United States and Canada as well as in the Asia off the coasts of Japan and China. Scallops are commonly processed for their abductor meat although in some markets they are sold with the roe intact. Two common market varieties are the larger variety of Sea Scallops and the smaller variety of Bay Scallops.  Sea scallops are sorted and sold according to size using a count per pound. Sea scallops can range from 10 to 40 per lb./450 g, common sizes that you may find in markets are 10 to 20, 20 to 30 or 30 to 40. Extra large scallops are labeled with a U/10 or U/12 designation signifying a yield of under 8 or 10 scallops per 1 lb./450 g.


Cephalopods have an internal shell called a pen or cuttlebone and include squid (calamari), octopus, and cuttlefish. These creatures have very tough connective tissue created by a crisscross of collagen that makes cooking them a challenge. They are best when mechanically tenderized, and either cooked minimally, or cooked for several hours.


Octopuses are a class of shell-less mollusks called cephalopods and there are about 300 varieties found in most of the world’s oceans. Octopuses are popular in the Mediterranean region especially in Greece, Italy and Spain, in Asia including Japan and Korea, and in Australia. They are related to the squid and cuttlefish and all three have a gland that emits a black ink when threaten by physical harm. The ink is sometimes used in culinary preparations to add color to pasta or risotto.


Squid, also known by its Italian name calamari, is a cephalopod mollusk with a soft body that is supported by an internal shell. Many of the 350 species of squid inhabit shallow coastal waters or live near the surface on the open sea, while others thrive in the depths of the ocean. They are popular in Europe, Japan, Australia, and the United States.


Related to squid and popular in the Mediterranean and Asia, the cuttlefish is a cephalopod mollusk with a flatter body than that of the squid, a closely related species. The cuttlefish adopts the color of its environment as camouflage. The white flesh of the cuttlefish is very firm and is similar to squid in texture.


Gastropods, also known as univalves, are known for their single shell, are saltwater, freshwater, and terrestrial mollusks which include abalone, conch, and snails.


Abalone have flattened, slightly spiraled shells, soft white body, and a muscular foot, and clings to rocks in cold water. It is found along the coasts of New Zealand, South Africa, Australia, Western North America, and Japan. There are over 100 varieties found around the world, but many are in danger from overfishing. Commercial abalone fishing in the United States is band, but some farming is being done in California, Hawaii, and Japan.  The white meat is tough and is often tenderized by pounding with a mallet, and is sliced thin for eating raw, sautéing, or grilling. The texture and flavor is similar to calamari.


Conch is a large snail found in warm waters of the Atlantic and the Caribbean from Florida to Brazil. It is popular in the Florida Keys, Puerto Rico, and other Caribbean islands. Conch in the United States is listed on the endangered species list so it must be imported from other areas of the Caribbean. Conch meat has a mild, sweet clam-like flavor, but like abalone it is extremely tough and must be tenderized before cooking.


Varieties of land and water snails are consumed in various cultures, better known by the French term escargot. The French “petit gris” (for little gray) and the larger “très gro” or Roman Snails, are the most popular. Snails are rarely sold fresh, but more likely canned requiring little preparation. Indonesia, is a large producer of snails along with Greece, Turkey, and Nigeria.


Sea Urchin

From the Greek word for “Spiny Skin”, the most notable edible entry in this category are Sea Urchins. The edible park of the sea urchin is the row and it is usually eaten raw or ceviche style.

Sea Urchin

A small hard-shelled invertebrate marine animal that lives in coastal waters, the sea urchin has a spherical shell and is covered with spines. The edible portion of this unisexual animal is the ovaries, and also known as the "coral," and the liquid that surrounds them. The coral is an orange color similar to that of a scallop. The sea urchin is found in most seas, but many of the almost 500 species are inedible and some emit poisonous venom. Sea urchins are sold live whole or corals only and are extremely perishable. Thick sturdy gloves are needed when handling or opening the sea urchins.