4 - Production of Marine Oils

Abstract

This chapter is divided into two parts: production of crude fish oil and the further processing of the crude oil through the various refining and concentration steps. Fish harvesting methods depend upon the targeted species. Pelagic fish, which school in large numbers and feed near the surface, are caught by purse seine. Some fish are located midway in the water column or near the bottom and these are generally caught by a trawler. A large net is dispatched from the rear of the vessel and towed through the water. Other harvesting methods involve long lines of baited hooks, sometimes several miles long. Trap nets are stationary nets on poles in rivers and bays. They are constructed in such a way that the fish swimming in the river or bay are directed along the net into a holding area or trap. The raw material for fishmeal and oil production contains about 80% liquid (water and lipid) and 20% solids (protein and minerals). In order to produce fishmeal and oil, the liquid must be removed from the solids. For the production of fish oil and fishmeal, the fish are first cooked in long cylindrical cookers, which have either hollow flights or a hollow outer shell through which steam is introduced. Fish oil can also be produced by solvent extraction, which is the old fish protein concentrate process.