Fish kairomones alter life cycle and growth of a calanoid copepod

In this study, we evaluate the effects of chemical information present in exudates of the zooplanktivorous fish Cnesterodon decemmaculatus (Poeciliidae) on the life cycle and growth of the planktonic copepod Notodiaptomus conifer. Semi-static assays were carried out using five concentrations of fish water (FW; 0.41–3.3 fish L−1), and a control (without fish). Copepods responded to FW by faster development and earlier maturation at smaller body size which resulted in a decline in the number of eggs in the first clutch. The proportional duration of each larval stage was not modified in the presence of fish chemical information, indicating that N. conifer maintained an equiproportional development according to the growth model proposed for copepods. Some parameters of the copepod life history changed depending on FW concentration, while other responses were induced merely by the presence of fish exudates, regardless of concentration. This study shows that calanoid copepods display as clear individual life history responses to kairomones as those that have been known for cladocerans, since 1980s. The observed responses are consistent with physiological mechanisms acting directly on development and constitute an example of the importance of predator–prey interactions as a selective force in aquatic environments.