DAPHNIA MAGNA FOOD STUDY TEST

Abstract

The macroinvertebrate, Daphna magna, extensively in environmental toxicity testing. The Environmental Protection Agency is used Therefore, (EPA) has been commissioned to develop standard testing procedures. Most variables have been standardized, but the current trout chow and Selenastrum capricorntum (TC/S) food combination recommended by the EPA is highly variable in its capacity to sustain daphnid cultures due to the trout chow. Research was conducted to determine if a more defined food source could be developed to provide more consistent toxicity test results. A combination of Selenastrum capricorntum plus Ankistrodesmus falcatus (S/A) live and freeze-dried at 13.6, 6.8, and 3.4 mg/L was compared with the EPA's standard TC/S at 6.8 mg/L in terms of daphnid survival, growth, and reproduction in two 21 day chronic tests. The live algae-fed daphnids were as healthy as the TC/S-fed daphnids for all tested endpoints, however the freeze-dried algae-fed daphnids had poor reproduction and survival. Based on the 21 day chronic food tests, one alternative food (S/A, live at 6.8 mg/L) was selected for comparison with the TC/S in a copper toxicity test. The objective was to determine the relative sensitivity to copper of daphnids fed the alternative food. The algae-fed daphnids appeared to be sensitive to copper at a concentration as low as 25.0 mg/L. The TC/S-fed daphnids appeared sensitive to the 100 mg/L level only. Thus, the algae-fed daphnids were more sensitive than the TC/S-fed daphnids by a factor of four. This could have been due to copper chelating by the TC/S food resulting in less copper available to affect the daphnids or to adsorption of copper by the particulate matter in the TC/S. Neither the freeze-dried nor the live algae proved to be a better standard food than the current TC/S for daphnids. testing is necessary to derive a better standard food.