Different oils differ markedly in their fatty acid composition: fish oils are unique in being rich in long-chain w3 polyunsaturated fatty acids, specifically EPA and DHA, which are recognised as having beneficial effects in humans (see Aquamax Newsletter 2).

Earlier studies in RAFOA established that blends of vegetable oils can replace fish oil for the major part of the growth period in several farmed fish: Atlantic salmon, rainbow trout, European seabass and gilthead seabream. The vegetable oil blends were designed to mimic the levels of total saturated, total monounsaturated and total polyunsaturated fatty acids in fish oils, and their high levels of omega-3 polyunsaturates, except of course that the omega 3 polyunsaturate was the C18 linolenic acid (18:3w3).

Terrestrial plants do not contain the EPA and DHA so important for human nutrition so that it is necessary to introduce fish oil containing diets as a finishing protocol to restore the required long chain omega-3 fatty acid profile of the flesh of the farmed fish.

Fatty acid compositions of oil

The figure shows the fatty acid compositions of oils used to generate suitable blends to replace fish oil in Aquamax. Noteworthy is the use of very high quality rapeseed oil produced by an award winning advanced technology; also the investigation of a novel oil, Camelina oil (usually known in English as gold-of-pleasure or false flax), up to now unexploited in fish diets and a possible alternative to linseed oil. 

Table: Values of the fatty acid compositions of different oils.