Oily fish, oil-rich fish or pelagic fish are those fish which have oils throughout the fillet and in the belly cavity around the gut, rather than only in the liver like white fish. Oily fish fillets may contain up to 30 percent oil, although this figure varies both within and between species. Oily fish generally swim in the pelagic zones of the oceans.

Oily fish are a good source of Vitamins A and D as well as being rich in omega 3 fatty acids. For this reason the consumption of oily fish has been identified as more beneficial to humans than white fish. Amongst other benefits, studies suggest that the omega 3 fatty acids in oily fish may help sufferers of depression, reduce the likelihood of heart disease and improve inflammatory conditions such as arthritis.