While fish oils are rich in omega-3 polyunsaturated fatty acids, vegetable oils mainly contain omega-6 polyunsaturated fatty acids and saturated fatty acids.  These differences may modify the metabolic processes involved in lipid storage.

However, INRA showed that the total replacement of fish oil by a mixture of vegetable oils had no effect on either growth or muscle lipid levels in the trout. However, feed containing the mixture of vegetable  oils caused a reduction in the levels of plasma cholesterol and circulating LDL (low density lipoprotein, transport proteins) and in the expression of the LDL receptor gene in the liver and adipose tissue.

A total replacement of fish oil by a mixture of vegetable oils is thus possible in the trout, although further studies are necessary to clarify the mechanisms responsible for the cholesterol-lowering effect of vegetable oils.