Trace nutrient deficiency in Daphnia magna cultured in standard medium for toxicity testing. Effects of the optimization of culture conditions on life history parameters of D. magna

The suitability of various synthetic media for the culture of Daphnia magna was tested. Daphnids cultured in a standard medium for toxicity testing proposed by ISO showed low reproduction, reduced growth, high numbers of undeveloped parthenogenetic eggs and high mortality of neonates and adults. As a feature, animals cultured in the ISO medium lost parts of their second antennae. It could be shown that this was caused by selenium deficiency. The addition of selenium to the ISO medium clearly improved the quality of this medium. However, results of several tests were more variable than when a medium with a complex trace element composition (medium M4) was used. Medium M4 has allowed continuous culture of daphnids for three years up to now without any signs of reduced viability or reproduction. A mean reproduction rate of about 140 progeny/parent daphnid was calculated from 19 non simultaneous experiments. Neither a fourfold increase nor a reduction to one tenth of the trace element concentration of M4 had any effect on reproduction, growth or survival of daphnids. It was shown in this study that ion-exchanger cartridges can leach detrimental substances into the matrix water. Therefore, only ultrapure matrix waters should be used for the preparation of culture media.