Polyunsaturated fatty acids (PUFA) are essential components in aquaculture diets, where an artificial food chain must be established (Bottino 1974; Rimmer et al. 1994). For many larval, or fingerling aquaculture species, the provision of PUFA (especially the omega-3 fatty acids EPA, DHA, and the omega-6 fatty acid AA is critical, and must be provided from either a "live" diet, usually via rotifers (eg. Brachionus plicatilis) or brine shrimp (Artemia sp.) as intermediates (Ostrowski & Divakaran 1990, Mourene and Tocher 1993a,b; Bell et al 1995; Southgate & Lou 1995) or an artificial diet. As adults, many species of finfish are reared on artificial (pelletised) foods that must also contain PUFA.

Commercial sources of PUFA for use within the mariculture industry are currently restricted to certain fish oils and microalgal species which are, respectively, under threat of over-exploitation and expensive to produce (New and Csavas 1995, Tacon 1995). The recent discoveries of bacteria and fungi that synthesise PUFA provide a novel and timely opportunity to develop biotechnological processes for sustainable and relatively cheap PUFA production.

Particular opportunities arise from the recent isolation of the following organisms:

1) Antarctic bacteria that produce the n-3 fatty acids EPA and DHA, and the n-6 fatty acid AA. (Antarctic CRC and University of Tasmania)

2) Marine fungi that produce high levels of both DHA and EPA. (CSIRO Division of Marine Research)

Research combining skills and expertise in microbiology, cell culturing and manipulation, marine oils and lipid chemistry, biotechnology and aquaculture nutrition are required to take advantage of the industrial opportunity presented. Scientific advances can be made in each of these areas.

In microbiology there is a need to develop targeted, intelligent screening protocols to optimise recovery of bacteria with biotechnologically useful traits such as PUFA production. There is also a need to integrate current knowledge of factors which affect microheterotroph growth and metabolic processes into the development of techniques to optimise production of desired compounds. Research integration is expected to lead to the development of technology with which high productivity can be achieved while using cheap culture media.

The application of state-of-the-art techniques in lipid chemistry will be applied to qualitatively and quantitatively evaluate PUFA production by microheterotrophs. The biotechnological challenge will involve devising stable formulations of whole cells and/or their extracts, and to transfer this technology from laboratory-scale trials through pilot-scale to commercial production systems.

As discussed above, the potential Australian Bacterial Single Cell (BSC) product(s) in this application should be able to meet some or all of the requirement for n-3 and n-6 fatty acids of larval and adult aquaculture species. In addition, the BSC products should be also able to provide a good protein source, and may have the potential to improve the fatty acid profile of product flesh. Thus, the proposed Australian product may have the potential to replace a significant proportion of the fish meal and fish oil currently used.

Industrial advantage will be gained from the application of the scientific knowledge developed during this project, in the incorporation of PUFA-producing bacteria or products derived therefrom into aquaculture food-chains.