Effect of Body Size on Toxicity of Zinc in Neonates of Four Differently Sized Daphnia Species

The sensitivity of neonates of four Daphnia species to zinc was tested in relation to their mean body size. These mean sizes of these four Daphnia spp were: D. magna , 0.813 ± 0.055 mm, D.␣pulicaria , 0.745 ± 0.063 mm, D. pulex , 0.645 ± 0.044 mm and D. galeata , 0.611 ± 0.058 mm. A positive relationship between EC 50 (24, 48) values and neonates size was found. The smaller the size of the daphnid the higher was the sensitivity to heavy metal toxicity. For all tested species did the EC 50 values decrease with time; the decrease was most marked for D. magna and the least for D. galeata . The EC 50 values of D. magna were higher than would be expected on basis of its body size.