Enhanced sensitivity to an insecticide carbaryl in Daphnia magna mediated by fish kairomone

Fish kairomone-exposed Daphnia produce smaller offspring than unexposed mothers. These smaller offspring are expected to be more vulnerable to pesticides because Daphnia show size-dependent chemical sensitivity. To evaluate the potential effects of fish kairomone on the acute toxicity of an insecticide, carbaryl, in D. magna, we compared the offspring produced by adults reared in the absence and presence of fish in terms of body length and 48-h EC₅₀. We also tested the sensitivities of juveniles of different ages but similar body sizes. The results indicated that sensitivity to carbaryl was not simply determined by the body size of D. magna. The tolerance of D. magna to pesticide may be strongly associated with individual energy storage conditions or metabolic costs generated by exposure to fish kairomone.