An oil derived from fish tissue is called fish oil. In general, it is obtained from oily fish like herring, tuna, anchovies, and mackerel. However, cod liver oil is sometimes made from the livers of other fish as well.
Fish oil is a common dietary supplement. It is high in omega-3 fatty acids, which are essential for your health. The omega-3 fatty acids you need could be obtained by taking a fish oil supplement if you don’t consume a lot of oily fish.