Marine Biology 111,461-465 (1991) Marine Biology © Springer-Verlag 1991 A study of the variations in lipid levels, lipid class composition and fatty acid composition in the first stages of Artemia sp. J.C. Navarro 1, E Amat 2 and J.R. Sargent 1 1 N.E.R.C. Unit of Aquatic Biochemistry, School of Natural Sciences, Stirling University, Stifling FK9 4LA, Scotland Instituto de Acuicultura de Torre de la Sal (C.S.I.C.), E-12595 Ribera de Cabanes, (Castell6n), Spain Date of final manuscript acceptance: August 9, 1991. Communicated by J. Mauchline, Oban Abstract. The lipid class composition and the fatty acid composition of total lipids of the cysts, newly hatched nauplii and 24-h-old metanauplii of a Spanish partheno- genetic diploid strain of Artemia sp. were studied. Sub- stantial differences in the total lipid level occurred among these stages, with a marked increase from the cyst to the nauplii being followed by a decrease in the metanaupliar stages. This variation affected the absolute levels (mg/g dry wt) of the total lipid classes and individual fatty acids, although the percent composition of the fatty acids in total lipid was essentially unchanged. An exception oc- curred during hatching in that the percentages of 16:0 and 16:1n-7 in total lipid decreased whereas that of 20: 5n-3 increased. The lipid classes showed higher varia- tion than the fatty acids both in absolute and in relative terms, and in particular, the ratio of phosphatidyl- choline: phosphatidylethanolamine decreased progres- sively from cysts to nauplii and metanauplii. The implica- tions of these findings for the use of Artemia sp. as a larval feed in aquaculture are considered. Introduction The brine shrimp, Artemia sp. is used in aquaculture as a live prey in any of its life history stages, but the nauplii directly hatched from the cysts are the most utilised food for crustacean and fish larvae (Kinne 1977). Given their higher energy content in comparison with the nauplii (Leger et al. 1986), attempts have also been made to use the decapsulated cysts (Sorgeloos et al. 1977) as food for fish (Leger et al. 1986, Dendrinos and Thorpe 1987) and crustaceans (Landau and Eifert 1985, Leger et al. 1986). The fatty acid profile of Artemia is one of the factors limiting its use as larval food, since nauplii from different stocks possess different amounts of highly unsaturated fatty acids (HUFA) essential for marine animals. This led Watanabe et al. (1978) to classify Artemia into two broad groups: fresh-water Artemia, lacking HUFA and only suitable for feeding freshwater animals, and marine type Artemia, in which some HUFA are present and are suit- able as food for certain stages of marine animals. It is then important to know the variations in the lipid compo- sition during these stages so as to assess their nutritional value. Variations in the lipid content and the fatty acid composition of total lipid during the first 24 h of life of Artemia nauplii were studied by Claus et al. (1979) using fresh-water-type samples (Watanabe et al. 1978) from Great Salt Lake and San Francisco Bay popula- tions. Watanabe et al. and Schauer et al. (1980) reported some data on variations in the lipid content and fatty acid composition of lipids from the cyst to the newly hatched nauplii from several strains. To the best of our knowl- edge, however, no studies have been carried out on the lipid classes and their variations during the first stages of the life history of Artemia, or on the variations of the fatty acid composition of total lipid during the first stages of a marine-type strain. The aim of this work was to analyze all of these changes, using as a model cysts and nauplii from the parthenogenetic diploid strain of Artemia from the "La Mata" lagoon (Torrevieja, Ali- cante, Spain). Materials and methods Artemia sp. cysts were harvested by the authors from the shores of the lagoon (July 1987), cleaned (Sorgeloos et al. 1977, Amat 1985, Navarro 1985), and stored in tightly sealed containers under anoxic conditions. Nauplii were hatched from the cysts in 34%0 S marine water, at 28°C and for the 38 to 40 h period that was the estimated t9o (Vanhaecke and Sorgeloos 1982) for this stock. Part of the nauplii was then harvested, and the remainder maintained for an additional 24 h under the same conditions before being finally harvested. By this time, the majority of the nauplii had already developed to the Instar II stage (Hentsehel 1968). Once harvested, the nauplii were thoroughly washed and blotted dry on filter paper. Prior to lipid extraction, the cysts were hydrated in distilled water until they were observed to be spherical. Preweighed aliquots of nauplii and cysts were dried at 105 °C for 24 h for moisture determinations. The lipids from triplicate samples of the remaining material were extracted