Analysis of the seasonal variation in biochemical composition of Daphnia magna Straus (Crustacea : Branchiopoda : Anomopoda) from an aerated wastewater stabilisation pond

The biochemical composition of Daphnia magna Straus, the dominant planktoni c crustacean of the waste stabilisation pond of Differdange (Grand-Duchy of Luxembourg), was quantitatively determined from October 1993 to July 1994. Over the sampling period, the average composition (mean +/- S.D.) was 271 +/- 64 mg proteins.g(-1) dry weight (DW), 100 +/- 28 mg lipids.g(-1) (DW), 96 +/- 58 mu g carotenoids.g(-1) (Dw), 49 +/- 14 mg chitin.g(-1) (DW) and 1 25 +/- 78 mg ash.g(-1) (DW). The seasonal variations of the biochemical com position were related to several ecological variables (water temperature, d issolved oxygen concentration, pH, water transparency, chlorophyll a concen tration and D. magna biomass). The chitin content was positively correlated to the water temperature as a result of the strong influence of this later variable on the moulting rate of the daphnids and, subsequently, on the ch itin synthesis by these organisms. The carotenoid content was positively co rrelated to the water transparency as a result of their photoprotective rol e in daphnids. The fluctuations of the lipid, protein and ash levels in D. magna depended to the food availability. Despite a seasonal variation in th e biochemical composition, D. magna appeared to have adequate lipid and pro tein levels to be used in aquaculture. Its carotenoid content is similar to fish meals used to color salmonid flesh and these organisms could be used for this purpose. The prospect of using D. magna for chitin extraction is w orth considering with respect to its significant chitin content, especially if highly valuable applications are aimed.