The principal fish oils of commercial importance include menhaden, herring, Pacific sardine, groundfish, tuna, and mackerel. Cod and shark are the chief sources of the fish liver oils. In general, the process of rendering is similar to that of whale oil, but it is usually carried out in on-shore establishments. The liver oils are also rendered by steam digestion of the whole or ground livers.
Commercial fish oils are used in paints and in the manufacture of lubricating greases. In the latter use, the oils are hardened by hydrogenation and converted to lime and/or aluminum soap bases. Other major end uses include insecticide emulsions, foundry core oils, and the fat-liquoring of leather. The liver oils are chiefly employed in the production of Vitamin A and D concentrates.