A Rapid Response Toxicity Test Based on the Feeding Rate of the Tropical Cladoceran Moinodaphnia macleayi

Recent research has reported that the feeding rate of the cladoceran Daphnia magna (measured over 24 h) is a sensitive indicator of toxicity. Using a methodology similar to that used for D. magna, a feeding test for the Australian tropical cladoceran Moinodaphnia macleayi was developed and the sensitivity of the test was compared with the currently used reproduction test. The results of the study revealed that the feeding rate of M. macleayi was a more sensitive indicator of toxicity than reproduction for cadmium; a mean concentration of 1.4 μg/L caused significant inhibition of feeding (P≤0.05), while reproduction was signficantly reduced at 3.1 μg/L (P≤0.05). No feeding inhibition was detected when M. macleayi were exposed to copper, despite significant mortality. The difference in feeding and reproductive responses of M. macleayi to cadmium and copper suggest differing modes of action for the two metals. The feeding test was validated on two samples of mine release water containing various metals. Results demonstrated that a cladoceran feeding test, performed over a 20-h period, was comparable in sensitivity to a reproduction test performed over a 5- to 6-day period.