Home Fish Facts Difference between Fish and Shellfish (Quick Read)

Difference between Fish and Shellfish (Quick Read)

by gvald

Shellfish is any food that comes from the sea (or, more rarely, from fresh water), with the exception of fish. It is a term that is only used in cooking, in food: the classification of shellfish differs from that of scientists, even if they are sometimes similar. There is a wide variety of shellfish.


What is the difference between fish and shellfish?

Shellfish is simply anything that comes from the sea, not including fish. There are three types of shellfish, mollusks, shellfish and crustaceans.


Shellfish consists mainly of shell or exoskeleton (like lobster or shrimp).


What are the different types of shellfish?

Recognizing mollusks

Mollusks are marine or terrestrial animals (like the snail). These little creatures have very specific characteristics. Indeed, they have a soft body and they have no vertebrae. There are several categories of mollusks: gastropods, bivalves, cephalopods and chitons.


Gastropods are land animals including snails and slugs. Bivalves are mollusks that have a shell. We can cite clams, oysters or mussels … Cephalopods are mollusks without a shell, such as octopus, squid and cuttlefish. The chitons are mollusks grazers whose shell is composed of plates.


As you will have understood, shellfish are above all mollusks! Mollusks without shells are few. This group is composed of marine animals such as squid, octopus or cuttlefish. These aquatic animals have tentacles.


In terms of cooking, it is important to know that these shell-less mollusks all have an ink sac that must be emptied. It is therefore preferable to ask your fishmonger to prepare them. These mollusks are often found on the shelves of fishmongers and have a firm and very appreciated flesh.


Grilled octopus, squid fritters, cuttlefish a la plancha… Fried, baked or grilled, these mollusks are delicious and can be prepared in different ways. Be careful though, cooking is very important. Indeed, when they are overcooked, these mollusks taste like rubber!


Recognizing shellfish

As we have already discussed, shellfish are primarily mollusks that have a shell. There are many of them and they can be divided into two main categories: bivalves and gastropods. Indeed, gastropods are not only land snails! Gastropods include whelks, periwinkles, abalones, etc. Bivalves include clams, oysters, mussels, cockles, razor clams, sea almonds, black scallops etc.


In the kitchen, shellfish are very popular, they are always present in shellfish platters. But be careful, shellfish are very fragile foods. It is very important to ensure their freshness to avoid indigestion. Gastropods and bivalves are sold live at the fishmonger’s. They must therefore be eaten very quickly. They must therefore be eaten very quickly, even the day of purchase.


If you buy them in a shop, check that the shells are well closed. You can also check the date of placing in the basket, if you buy oysters or mussels. When opening, the mollusc must retract, otherwise, the freshness is not assured. Moreover, if the shells do not open, you must throw them away!


Recognizing crustaceans

Finally, let’s talk about crustaceans. These aquatic animals are part of the arthropod group. They are quite different from mollusks without shells and shellfish. Indeed, the latter have articulated legs and a rigid carapace. The majority of crustaceans live in the sea, such as crabs, shrimps or spider crabs… But some crustaceans also live in fresh water, such as the crayfish!


On the cooking side, some crustaceans must be prepared alive. This is the case of crabs, crab cakes or lobsters. Indeed, to prepare them, it is necessary to plunge them alive in boiling water. Moreover, these shellfish often change color during cooking. Indeed, they become red or pink. This is due to a molecule that is destroyed during cooking, which causes the change in color of these aquatic animals.


Some crustaceans can be purchased already prepared, such as shrimp or langoustine. However, it is important to check the freshness. The eyes should always be bright and lively!


You are now better informed about the differences between mollusks, shellfish and crustaceans. All are shellfish, but not all have the same characteristics! Fish, on the other hand, are not shellfish. Remember to always check the freshness of these marine animals. Indeed, these products are very fragile and must be consumed very quickly.


Don’t hesitate to ask your fishmonger to make sure. Finally, be careful if you are eating shellfish for the very first time. Shellfish is highly allergenic and unfortunately not for everyone!


What is the difference between shellfish and fish?

Shellfish are invertebrate aquatic animals whose soft bodies are usually enclosed in a protective outer shell. Crustaceans, such as lobsters and crabs, are covered with a flexible, jointed shell.


Others, such as oysters and scallops, belong to the order of mollusks. Some mollusks, such as squid, have no external shell but have kept a small internal carapace.


How to differentiate certain shellfish?

You will admit that it can be complicated to find your way among all these names. Knowing that it is not always easy to differentiate these succulent shellfishs between them!


The most frequent confusion is between the lobster and the spiny lobster. The lobster has two long antennas and feeds only on plankton while the lobster has two large claws and is carnivorous.


Have you ever had doubts in front of a squid or a cuttlefish? The cuttlefish is small and round while the squid is elongated. The cuttlefish has one calcified bone and two arms while the squid has ten and is made of a feather.

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