Catalogus

Intra- and inter-laboratory variability in the determination of fatty acid composition was on average twice as high for quantitative data as it was for qualitative data. The intra-laboratory variation, averaged for all the laboratories for the feed and Artemia respectively, was as low as 3.3% and 2.7% for qualitative data, and 6.9% and 6.3% for quantitative data. In comparison, the average inter-laboratory variation for the major fatty acids in the feed and Artemia respectively, was 13.7% and 7.3% for qualitative data, and 24.5% and 11.5% for quantitative data. The higher variability in the quantitative, as well as qualitative data, for the dry feed may have been due to a higher variability in the extraction and/or methylation of the fatty acids from the extruded matrix of the diet compared to brine shrimp tissue. The laboratories using the Standard Method exhibited a somewhat lower intra-laboratory and inter-laboratory variation for the qualitative values than the laboratories applying their own in-house method. In contrast, the quantitative analyses revealed, particularly for the dry feed, a slightly higher variability for the laboratories following Standard Method. The overall variability in the present exercise, both on the intra-laboratory as well as inter-laboratory level, was significantly lower than that reported by Léger et al. (1989). The better accuracy obtained in the present exercise for the determination of fatty acid composition in Artemia nauplii is at least partially due to the stipulation of a standard procedure for hatching and analysis of the cyst sample in the instruction to the participants. Although it is more elaborate and solvent consuming than many current methods for fatty acid analysis in routine use, the ICES Standard Method may be used to intercalibrate the analytical procedures adopted by different laboratories to analyse fatty acids in Artemia and marine samples.