AbstractThe free-living nematode Panagrellus redivivus can be mass produced in monoxenic solid culture on Saccharomyces cerevisiae and therefore could be useful as a live food for marine fish or crustacean larvae in the rapidly expanding aquaculture industry. However, this will depend on their lipid and fatty acid composition and so this was investigated in mass produced P. redivivus grown on S. cerevisiae in three different media. Live nematodes were also incubated with [1-14C]-labelled fatty acids and the desaturation and elongation of the fatty acids were determined. The combined results from the growth trials on different media and the metabolic studies with labelled fatty acids indicated the presence of Δ9, Δ12, Δ6 and Δ5 fatty acid desaturase activities, and elongase activities active towards C18, C16 and shorter chain fatty acids. The presence of Δ15, and therefore the ability to produce n-3 polyunsaturated fatty acids, was suggested by the compositional data, but could not be conclusively established from metabolic studies.