THE LIPID-COMPOSITION OF EUPHAUSIA-SUPERBA DANA IN RELATION TO THE NUTRITIONAL-VALUE OF PHAEOCYSTIS-POUCHETII (HARIOT) LAGERHEIM

The fatty acid profiles of Euphausia superba, the Antarctic prymnesiop hyte, Phaeocystis pouchetii, and a temperate diatom, Phaeodactylum tri cornutum were analysed and compared. The lipid content, lipid class, f atty acid and sterol composition of E. superba fed on each cultured ph ytoplankton and a mixed diet of both species, were determined. No sign ificant difference was found between total lipid levels of E. superba reared on each of these different diets. Phaeocystis pouchetii, althou gh deficient in a number of the essential fatty acids, is apparently a n adequate food source for E. superba. The proportion of polyenoic fat ty acids varied within lipid classes although there was no significant difference between levels of the long chain polyunsaturate 20:5(n-3) in the total lipid of E. superba fed on these diets. The acid was foun d to be less than 1% of the total lipid in Phaeocystis pouchetii compa red to 37% in Phaeodactylum tricornutum. This suggests that krill may possess the ability to convert exogenous shorter chain fatty acids to 20:5(n-3) and 22:6(n-3). Significant differences were detected in the isomeric ratio of 16:1(n-7c)/16:0 between krill fed the diatom compare d to the prymnesiophyte diet. Significant differences were also detect ed in several shorter chain fatty acids and between fatty acids within their lipid classes. Such differences may have the potential to be us ed as biochemical signatures to provide information on food sources an d possible feeding grounds of E. superba. Phaeocystis pouchetii in a v ery late stationary phase, although not used in this feeding study, wa s found to contain 11% of 22:6(n-3) for which there are few substantiv e sources in natural algal populations.