Alternative dietary sources of nutrients

Of the world's total production of fish meal and fish oil, some 5% and 27% respectively goes into the salmon feed production market. Increased concerns about the sustainability of industrial fishing and the morality of using fish to grow more fish has intensified the search for alternative sources. Scarcity of fish in some parts of the world has led to increases in fish meal prices which are naturally passed down the line to the farmer.

Fish oil is characterised by a large proportion of long chain, polyunsaturated fatty acids (PUFAs) which are essential for growth. High levels of PUFAs in the diet of humans are encouraged from a health aspect. It is known that oils derived from plants (soya, sunflower, rapeseed) also contain some PUFAs but do not have the range found in fish oils nor do they have a high proportion of linolenic (n-3) and linoleic (n-6) fatty acids. Thus it would not be possible to use plant oils alone. However, trials in which dietary lipids are made from combined fish and plant oil sources (3:1 ratio respectively) indicate no problems with fish growth, health or body composition and carcass quality. The only area of contention is that of taste - argument continues as to whether there is an alteration of taste to a less 'fishy' one.

Replacement of the protein component of farmed fish diets is not so straightforward due to the requirement of the 10 essential amino acids. Alternative sources are usually lacking in one or more of these, meaning that they have to be either specifically isolated from fish meal or manufactured. This is an expensive process. Work continues on finding appropriate substitutes.