Seafood includes any form of food taken from the sea. Seafood is any form of sea life regarded as food by humans. Seafood prominently includes fish and shellfish. Most of the seafood harvest is consumed by humans, but a significant proportion is used as fish food to farm other fish or rear farm animals. Some seafoods (kelp) are used as food for other plants (fertilizer). In these ways, seafoods are indirectly used to produce further food for human consumption. Products, such as fish oil and spirulina tablets are also extracted from seafoods. Some seafood is feed to aquarium fish, or used to feed domestic pets, such as cats, and a small proportion is used in medicine, or is used industrially for non-food purposes (leather).
The harvesting of wild seafood is usually known as fishing or hunting, and the cultivation and farming of seafood is known as aquaculture, or fish farming in the case of fish. Seafood is often distinguished from meat, although it is still animal and is excluded in a strict vegetarian diet. Seafood is an important source of protein in many diets around the world, especially in coastal areas. Fish are aquatic vertebrates which lack limbs with digits, use gills to breathe, and have heads protected by hard bone or cartilage skulls.
There are several varieties of fish, like larger predatory type, which includes sharks, tuna, marlin, swordfish, mackerel, salmon and smaller forage fish, like, herring, sardines, sprats, anchovies, menhaden. The smaller forage fish feed on plankton, and can accumulate toxins to a degree. The larger predator fish feed on the forage fish, and accumulate toxins to a much higher degree than the forage fish. Freshwater fish live in rivers, lakes and ponds. Some seafood groups are carp, tilapia, catfish and trout. Generally, freshwater fish lend themselves to fish farming more readily than the ocean fish, and the larger part of the tonnage reported here refers to farmed fish.
Fish is a highly perishable product. The fishy smell of dead fish is due to the breakdown of amino acids into biogenic amines and ammonia. Fresh fish is a highly perishable food product, so it must be eaten promptly or discarded; it can be kept for only a short time. In many countries, fresh fish are filleted and displayed for sale on a bed of crushed ice or refrigerated. Fresh fish is most commonly found near bodies of water, but the advent of refrigerated train and truck transportation has made fresh fish more widely available inland. Long term preservation of fish is accomplished in a variety of ways. The oldest and still most widely used techniques are drying and salting. Desiccation (complete drying) is commonly used to preserve fish such as cod. Partial drying and salting is popular for the preservation of fish like herring and mackerel. Fish such as salmon, tuna, and herring are cooked and canned. Most fish are filleted prior to canning, but some small fish (e.g. sardines) are only decapitated and gutted prior to canning. Fish is among the most common food allergens. Iceland, Japan, and Portugal are the greatest consumers of seafood per capita in the world.