Seafood: not all the same
Types of Seafood
The foods we derive from the aquatic environment fall broadly into two major categories,
fish and
shellfish. The marine mammals, such as whales, dolphins, seals and porpoises, do not constitute a major food source, at least for Western Europe, so will not be considered further.
Fish
Though fish can come from freshwater and/or saltwater environments, from a nutritional point of view there is not a big difference, so this distinction will not be explored further. The major division within the fishes is between those with bones, and those without, the so-called
cartilaginous fish. The latter include sharks, skate, rays and dogfish. Dogfish (also known as huss, or rock salmon) and skate are moderately popular in the UK, accounting for around 2% of fresh fish landings. The remaining 98% (excluding shellfish) is made up of the bony fish, and this group is split into two, on the basis of feeding habits.
Demersal fish
This group represents just over half of all UK fresh fish landings, and consists of the so-called white fish, the low-fat fish.
Demersal fish feed deep in the water, or even on the sea-bed, and catching technology is adapted to this. Cod, haddock, plaice and whiting make up 65% of this group, with sole, saithe/coley, ling and monkfish important members of the rest.
Pelagic fish
These are fish which feed more in the surface layers (though at different stages of the breeding cycle, some pelagic fish can temporarily become demersal). The
pelagic fish are primarily those with higher levels of lipid in the flesh, which gives them non-white flesh. The major members of this group are herring and mackerel, which make up over 90% of fresh pelagic landings in the UK. Spratts, pilchards (mature sardines) and tuna are also sometimes landed in the UK, though tonnages are not large at present. Nutritionally, salmon and trout are probably closer to this group than any other. Being mainly farmed fish, there are few reliable published figures to indicate production or consumption levels, but both are significant contributors to fish intake.
Shellfish
This group includes not only the creatures we normally think of as shellfish, but other marine life-forms without apparent shells, such as squid and octopus. There are two groups of shellfish of importance in human food, the
mollusca and the
arthropoda.The mollusca consists of bivalves (with a two-piece shell) such as oysters, mussels and scallops, and univalves with a one-piece shell such as whelks, limpets and cockles. The cephalpods, such as squid, cuttlefish and octopus also fall into the univalve category. The arthropods of relevance to human nutrition comprise the crustacea, a group which includes lobster, prawns, shrimps, crayfish and crabs.
