FEATURE Porphyridium (Flynn and Flynn 1992), the dinoflagellate Oxyrrhis (Flynn and Fielder 1989), and the diatom Nitzschia (Jackson et al. 1992).
Macroalgae (seaweeds) of many kinds can form extensive stands with high biomass density
Pigments A few algae are used as sources of pigments in fish feeds. Haematococcus is used to produce astaxanthin, which is responsible for the pink colour of the flesh of salmon. Spirulina is used as a source of other carotenoids that fishes such as ornamental koi can convert to astaxanthin and other brightly coloured pigments. Dunaliella produces large amounts of beta-carotene.
Lipids In addition to its high content of highquality protein, fishmeal provides lipids rich in ‘PUFAs’, or polyunsaturated omega-3 and omega-6 fatty acids. These are the ‘fish oil’ lipids that have become highly prized for their contribution to good cardiovascular health in humans. But it is not always appreciated that algae at the base of the aquatic food chain in fact originate these ‘fish oil’ fatty acids. These desirable algal fatty acids are passed up the food chain to fish, and they are indeed essential nutrients for many fish. Algae have been recognised as an obvious alternative source of these ‘fish oil’ fatty acids for use in fish feeds (Miller et al. 2008), especially eicosapentaenoic
acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (ARA). There is a substantial literature devoted to analysis of the PUFA content of microalgae, particularly those used in aquaculture, because they have long been recognised as the best source of these essential nutrients
for production of zooplankton necessary for the first feeding of larval fish, as well as filter-feeding shellfish. Many shellfish producers are aware the sterol profile of feed lipids is of critical importance, but much less attention has been paid to the importance of the
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September-October 2012 | International AquaFeed | 11