The presence of chemicals exuded by fish affects the life-history responseof Ceriodaphnia cf dubia to chemicals with different mechanisms of action

The toxicity of chemicals with different mechanisms of action (3,4-dichloro aniline, fenoxycarb, and chlorpyrifos) to the cladoceran Ceriodaphnia cf. d ubia was examined in the presence and absence of chemicals exuded by fish, termed fish kairomones. A range of life-history traits were examined. inclu ding mean brood sizes, survival, net reproductive rate (R-o) and population growth rate (r). Cladocerans exposed to 3,4-dichloroaniline showed similar sensitivities in the presence and absence of fish kairomones with respect to all of the life-history traits examined. The presence of fish kairomones reduced the sensitivity of cladocerans to fenoxycarb with respect to mean brood sizes and r but increased their sensitivity in terms of R-o. The pres ence of fish kairomones increased the sensitivity of cladocerans to chlorpy rifos with respect to survival, r, R-o, and mean brood sizes. The general t rends observed were similar to those shown when C. cf. dubia was exposed to these chemicals under low food conditions, and it is suggested that the ef fects of fish kairomones on toxicity may be attributed to the reduction in feeding rates observed when C. cf. dubia is exposed to fish kairomones.