EFFECTS OF DIET ON 7-DAY CERIODAPHNIA-DUBIA TOXICITY TESTS

The purpose of this study was to evaluate the effects of four diets on the results of seven-day Ceriodaphnia dubia toxicity tests. Survival and reproduction were used as indices to detect the sensitivity of thi s species to acute and chronic copper stress. All toxicity tests were conducted using the moderately hard reconstituted water recommended in 1989 by the U.S. Environmental Protection Agency. Diet differentially affected the acute and chronic toxicity of copper. Daphnids fed Selen astrum capricornutum (alga) showed the greatest sensitivity, followed by those fed the alga Chlamydomonas reinbardti, then by animals fed a Yeast-Cerophyll(TM)-Trout Food (YCTF) mixture plus Selenasrum, and fin ally by animals fed YCTF alone. These differences may result from the poor nutritional adequacy of Selenastrum when fed alone, the different caloric contents of the diets, the increased toxicant uptake by the o rganisms through ingestion of copper-laden algal cells, and/or copper ions sequestered by fats and insoluble substances in YCTF. We recogniz e that diet is an important variable in seven-day toxicity tests, and that the selection of a diet should not be based only on its effects o n long-term culturing of C. dubia, but also on its possible effects on test results.