Shellfish, invertebrates covered by some type of outer shell, are divided into two groups—crustaceans and mollusks. Crustaceans have crustlike shells with segmented bodies. They include crabs, lobsters, and shrimp. Mollusks have soft structures partially or totally enclosed in a hard shell.
One type of mollusk is the bivalve (an animal that lives inside a hinged shell), a group that includes clams, oysters, scallops, mussels, and abalones. To be certain that the bivalves you purchase are safe, buy from reliable dealers who know and can control their sources. If you are harvesting your own, make sure the water is safe and free of pollutants—check with the local fish and game authorities. While mollusks are often eaten raw, it can be chancy, so it is safer to cook them before serving. High temperatures destroy most of the life-threatening organisms they harbor.
Another class of mollusks are the cephalopods, which includes squid and octopus.
Crustaceans and cephalopods are found in deeper waters that are less likely to be polluted than shallow waters. Further, they do not tend to retain pollutants in the high concentrations that bivalves do.
You can buy whole hard-shell crabs either alive or fully cooked. When buying live crabs, they must be kept alive until cooked (for safety), so make sure they are kicking when you purchase them. Fortunately it’s become easier and easier to find these live crustaceans. They will keep for a day or two in the refrigerator. Do not keep them in water. Instead leave them in a paper bag in the cold fridge. Crab claws are generally not pegged (held shut with wooden pegs or rubber band) as lobster claws are, so be wary when you pick them up as they can pinch.
Soft-shell crabs should only be bought live. They too should be refrigerated (not in water). No need to put them in a paper bag, though, because they can’t escape.
Fresh, packed crabmeat is available in most areas frozen or canned, usually fully cooked. As with all seafood, it should have a fresh, sweet smell. Crabmeat comes in several styles: lump, backfin, or flaked. Lump meat, the large white chunks of body meat, is considered the finest. Backfin meat comes in smaller chunks than lump meat and may be used the same way in most recipes. Flaked meat comes from various parts of the crab. It is less expensive than lump and backfin meat and may be mixed with them in recipes. One pound of lump, backfin, or flaked meat will serve 4 to 6, depending on the recipe.
Fresh crabmeat is sometimes sold canned, having first been pasteurized. The meat will remain fresh as long as the can is not opened. Once opened, keep it refrigerated and use within a day or two. Pasteurized cooked crab may be frozen, but its taste won’t be as sweet and its texture may be spongy. When using crabmeat, be sure to pick it over to remove small bits of shell and cartilage.
Fresh lobsters are available in many markets, where they can be found swimming in tanks. In this country the most popular variety is the Maine lobster with its delicious claw meat. But there are other equally delectable varieties. The spiny lobster is found in Europe and off the coast of Florida. This is the variety sold here as rock lobster tail. The langoustine or scampo (as it is called in Italy) is also available here but is less popular than Maine and spiny lobsters. It is found exclusively in European waters.
When buying live lobsters, make sure they are fairly active. Store live lobsters in a paper bag or in the bag they came in (not in a sealed plastic bag) in the refrigerator until you are ready to cook them. If buying cooked lobster, use within a day.
Lobster meat is also available in the form of frozen, uncooked tails (rock lobster). Cooked lobster meat is available fresh, frozen, or canned.
Edible meat usually equals about one-fourth of the lobster’s weight, so a 2-pound lobster will yield about ½ pound of meat. A large or jumbo one will often supply enough meat for 1 to 2 servings, depending on how it is prepared.
Lobster is graded according to weight: 1 pounders are called chickens; 1¼ pounders are called quarters; 1½-pound lobsters are called halves; 2 pounders are selects, and 2½ pounders are jumbos. There are some that grow as big as 20 pounds (or more).
If you are looking for a good deal, ask if the market carries culls; these are lobsters that are missing one claw.
Probably the most popular shellfish around, shrimp are available in several forms: fresh either with their shells on or peeled and deveined; and frozen, shell-on or peeled and deveined. Fresh, uncooked shrimp should be firm in the shell, not soft and mushy. Frozen shrimp work very well in recipes; in fact the shrimp you buy “fresh” in a seafood market or the seafood department of a supermarket is actually thawed frozen shrimp, since shrimp are usually frozen right after they are caught.
The number of shrimp in a pound will vary with size, from tiny (up to 160 per pound) to colossal (under 8 per pound).
Hard-shell clams include butter clams, quahogs (also called cherrystones or littlenecks), Pacific butter clams (smaller than the eastern variety), razor clams, and Pismo clams. Soft-shell clams, also known as steamers or longnecks, are also available.
Clams can be found year-round and are generally sold by the dozen. When shucked, they are sold by the pint or the quart. Clams sold in the shell should be alive when bought. Hard-shell clams will be tightly closed. If slightly open, they should close tightly when tapped. Soft-shell clams may be partially open because of the long siphon or neck extending from inside their shells.
When buying shucked clams, look for plump ones with a fresh, clear surface, packed in their liquor. Store all fresh clams, shucked or unshucked, in the refrigerator until you are ready to prepare them. Shucked clams should be used within a day, while clams in the shell can keep for a few days. You can freeze shucked clams, in well-sealed containers, cooked or uncooked, for up to 3 months. If uncooked, cover them in their liquor first. If cooked, add some stock or other liquid before freezing.
The varieties of these flavorful mollusks are innumerable. Almost 90 percent of the American oyster catch comes from the Atlantic. The rest comes from the Pacific or the Gulf of Mexico off the Louisiana coast. Pacific oysters are creamy with a slight mineral taste, while Atlantic oysters tend to be brinier.
Oysters are best in flavor from September through April, when they are not spawning. They may be marketed alive in the shell, sold by the dozen, or shucked and sold by the pint or quart. Shucked oysters may also be found packed in jars, frozen, or canned.
When buying oysters in the shell, make sure they are alive—the shells will be tightly closed. Shucked oysters should be plump and sold in clear, clean, fresh-smelling liquor that is free of sand. This tasty liquor adds flavor to soups and sauces.
Shellfish have gotten a bad rap over the years for their cholesterol content. While it’s true that some shellfish have a higher cholesterol content than low-fat finfish, they are very low in saturated fat. And it is saturated fats (and trans fats) that are the real culprits in high levels of blood cholesterol. If the food you are eating is high in cholesterol but low in saturated fats, its impact on your cholesterol levels is insignificant.
The chart below lists the cholesterol counts in shellfish as well as saturated fats and omega-3 fatty acids (since shellfish do actually provide some of these heart-healthy fats). The chart is organized by omega-3s, from high to low. To put the numbers in the chart into perspective, a 3-ounce piece of broiled sirloin has 65 milligrams of cholesterol and 2.5 grams of saturated fat; a 3-ounce portion of cooked chicken breast has 72 milligrams of cholesterol and 0.9 gram of saturated fat.
| SHELLFISH (3 OUNCES COOKED) | OMEGA-3S (G) | SATURATED FAT (G) | CHOLESTEROL (MG) |
| SCALLOPS | 0.8 | 0.6 | 34 |
| MUSSELS | 0.7 | 0.7 | 48 |
| SQUID | 0.5 | 0.9 | 239 |
| CRAB | 0.4 | 0.2 | 85 |
| OYSTERS | 0.4 | 0.6 | 32 |
| SHRIMP | 0.3 | 0.3 | 166 |
| OCTOPUS | 0.3 | 0.4 | 82 |
| CLAMS | 0.3 | 0.2 | 57 |
| CRAYFISH | 0.2 | 0.2 | 117 |
| LOBSTER | 0.1 | 0.1 | 61 |
Shucked oysters should be eaten within a day as they spoil quickly. Oysters in the shell can be stored in the refrigerator for a day or two. Oysters may be stored in the freezer in the same way as shucked clams.
Scallops, with their buttery texture and delicately sweet flavor, need little embellishment. There are two kinds of scallops sold in this country, both available fresh or frozen. The tiny cream-colored bay scallops come from shallow waters. The larger white sea scallops are dredged from deep waters. Diver scallops are sea scallops that are collected by divers, who pick only the largest.
Scallops should be fresh, sweet smelling, and plump. They should have a moist appearance but should be sold without any liquid. To appreciate their delicate flavor, you should eat them soon after they are caught. Purchase fresh, and keep for no longer than 24 hours after purchasing. Scallops may be stored in the freezer in the same manner as shucked clams.
The most popular mussels are blue mussels and green-lipped mussels. The blue mussels are found all over the world, but mostly along the Pacific and Atlantic coasts. Green-lipped mussels come from New Zealand. Mussels can be found both wild and farmed, but chances are the mussels you are getting at your local seafood market are farmed. Mussels should be tightly closed and their shells should not be cracked. Once purchased, they should be stored in the refrigerator and used within a day.
You can find both squid and octopus in fish markets, either frozen or thawed. While you can get fresh squid and octopus from farmer’s markets, what you find in the seafood store has usually been frozen and thawed. Once purchased, they should be refrigerated and used within a day; or you can freeze them for use later.