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The use of live prey is still necessary for a large number of raised ¢sh species. Small sized rotifers are usually used as live preys during the ¢rst days of feeding in small mouth ¢sh. An alternative to this is the use of copepods as prey for ¢rst feeding. In this study, the sizes, weight and biochemical contents of two copepods and one rotifer species raised on similar algal food conditions were compared. Rotifers contained a higher proportion of essential amino acids in the free amino acid (FAA) fraction (43%) than copepods (30^32%). However, rotifers had lower levels of important fatty acids like DHA (7% compared with 23^32% in copepods) and their DHA/EPA ratio was lower than that in copepods (0.54 compared with 1.35^1.63 in copepods). The FAA pattern of the preys tended to be species-speci¢c and its implications from an aquaculture point of view is discussed. In contrast, the-protein bound amino acids tended to be very conservative among the studied organisms. The second part of the work is focused on 'the price' of hatching in Acartia tonsa eggs before or after cold storage at 3 1C. The fatty acid contents in A. tonsa tended to decrease with the storage time. It also decreased with hatching of the nauplii, but its proportion compared with the dry weight remained constant.The table also presents the DHA/EPA ratio and the (EPA1DHA)/total FA ratio and, ¢nally, the proportion of essential amino acids in the free amino acid pool for the di¡erent live feed organisms. DW, dry weight; DHA, docosahexaenoic acid; EPA, eicosabentaenoic acid.Aquaculture Research, 2006, 37, 756^772 Biochemical and technical observations larviculture G Drillet et al.

Copepods have proven to be an ideal source of live food for the production of marine fish larvae in aquaculture. Therefore, there is a need to develop new methods for production and storage of copepod eggs that can be hatched and used at fish farms. In the present study quiescent eggs of Acartia tonsa were stored for periods up to 35 weeks at different temperatures, salinities and oxygen conditions in a full factorial experiment. None of these storage conditions seemed to induce diapause in eggs even though this has been reported by other authors. The most promising storage conditions were those involving low temperature (<5°C), medium salinity (10–20 ppt) and anoxia. The practical aspects of these results for aquaculture are discussed.