How Do Shellfish Differ From Other Fish And Fish? How Do Shellfish Differ From Other Fish

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.

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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


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

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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.

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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.

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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.

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