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

Daphnia swimming behavior during vertical migration

We observed the individual swimming behavior of a clone of Daphnia hyalina swimming freely inside a mesocosm-scale plankton tower. Changes in light intensity and the presence or absence of fish smell induced vertical migration through similar to 4 m. The results of analysis of video records of individual swimming behavior include the following: when lights were turned on, Daphnia moved down by fast downward swimming, not by sinking or moderate swimming; when lights were turned off, the Daphnia rose by fast upward swimming, not by upward moderate swimming (with hops). Moderate swimming was nearly horizontal and fast swimming was nearly vertical. Fish smell increased the proportion of the population swimming fast in response to a light stimulus, but inhibited the expression of sinking behavior. These results, interpreted in the light of the predator-avoidance hypothesis of diel vertical migration, suggest that vertical migration through fast swimming is less dangerous than vertical migration via either sinking or vertical moderate swimmin

Appendix A. A table showing the data set of 41 well-studied lakes.

A table showing the data set of 41 well-studied lakes