Development of farmed fish: a nutritionally necessary alternative to meat

The projected stagnation in the catch from global fisheries and the continu ing expansion of aquaculture is considered against the background that fish meal and fish oil are major feed stocks for farmed salmon and trout, and al so for marine fish. The dietary requirement of these farmed fish for high-q uality protein, rich in essential amino acids, can be met by sources other than fishmeal. However, the highly-polyunsaturated fatty acids eicosapentae noic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) present in high conc entrations in fish oil are essential dietary constituents for marine fish a nd highly-desirable dietary constituents for salmonids. Currently, there is no feasible alternative source to fish oil for these nutrients in fish fee ds. Vegetable oils rich in linoleic acid (18:2n-6) can partially substitute for 20:5n-3 and 22:6n-3 in salmonid and marine-fish feeds. However, this i s nutritionally undesirable for human nutrition because the health-promotin g effects of fish-derived 20:5n-3 and 22:6n-3 reflect a very high intake of 18:2n-6 relative to linolenic acid (18:3n-3) in Western diets. If partial replacement of fish oils in fish feeds with vegetable oils becomes necessar y in future, it is argued that 18:3n-3-rich oils, such as linseed oil, are the oils of choice because they are much more acceptable from a human nutri tional perspective, especially given the innate ability of freshwater fish, including salmonids, to convert dietary 18:3n-3 to 20:5n-3 and 22:6n-3. In the meantime, a more judicious use of increasingly-expensive fish oil in a quaculture is recommended. High priorities in the future development of aqu aculture are considered to be genetic improvement of farmed fish stocks wit h enhanced abilities to convert C-18 to C-20 and C-22 n-3 polyunsaturated f atty acids, enhanced development of primary production of 20:5n-3 and 22:6n -3 by single-cell marine organisms, and continuing development of new speci es.