Oily fish are fish species with oil (fats) in soft tissues and in the coelomic cavity around the gut. Their fillets may contain up to 30% oil, although this figure varies both within and between species. Examples of oily fish include small forage fish such as sardines, herring and anchovies, and other larger pelagic fish such as salmon, trout, tuna, swordfish and mackerel.
The large open-water Atlantic bluefin tuna is an oily fish.
Most small forage fish, like these schooling anchovies, are also oily fish.
Oily fish fillet (salmon – bottom) contrasted with a white fish fillet (halibut – top)
Grilled salmon, an oily fish
Forage fish, also called prey fish or bait fish, are small pelagic fish that feed on plankton and other tiny organisms. They are preyed on by larger predators, including larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding. They include particularly fishes of the order Clupeiformes, but also other small fish, including halfbeaks, silversides, smelt such as capelin and goldband fusiliers.
These small goldband fusiliers are typical forage fish. They swim in large schools for protection from larger predators.
Copepod
Herring ram feeding on a school of copepods
Image: Anchovy closeup
