Ethanol:: a better preservation technique for Daphnia

A 4% formalin-40% sucrose solution has been used by limnologists for three decades as the preferred freshwater zooplankton preservative because it kills and fixes cladocera (Branchiopoda) with relatively little distortion. Because of the increasing evidence of health hazards related to formalin, we sought an alternative, safer preservative that satisfies the need for low distortion. Our results suggest the ethanol preservative methods (70% and 95% treatments) are as good or better as using 4% sugar formalin to fix and store samples. Our results indicate the best method is to fix samples in 95% EtOH followed by storage in 70% EtOH. This technique gave us the least frequent distortion, the highest average number of eggs per female, and the fewest embryos lost from the brood chamber. None of the techniques appeared to have positive or negative effects on body length. Using hot water to fix animals before storage is not recommended.