Aquatic toxicology of salinity and silver in Daphnia magna : a comparative study of standardized chronic endpoints and progeny Phototaxis.

Behavioral bioassays with the model freshwater cladoceran Daphnia magna have the potential to serve as nontraditional but sensitive endpoints of sublethal stress in the field of ecotoxicology. However, few studies have examined the comparative sensitivity of phototaxis perturbations to standardized endpoints in chronic toxicity testing protocols. D. magna 21 d chronic toxicity studies were conducted with model stressors of salinity (NaCl) and dissolved silver (Ag+). Phototaxis assays of progeny response to relative light changes in small water columns were conducted of each brood. Results indicated predominantly decreased phototactic behavior in comparison to control brood performance at common ecotoxicological thresholds. Phototaxis assays showed effects at treatment levels below the 21-d adult reproduction LOEC value in broods 2, 3, 5 and 6 in the salinity study and broods 2, 5, and 6 in the silver study. Future refinement of robust and potentially highly ecologically relevant behavioral assays such as phototaxis in combination with traditional and nontraditional endpoints may prove useful in characterization of assessment factors.