Common carp and goldfish discern conspecific identity using chemical cues

Behavioural responses of sexually-immature goldfish and common carp, two very closely related species of fish, were tested in a two-choice maze to determine if they use species-specific pheromonal attractants. Responses of these species to each other's washings and five other fish species were tested in a maze. We hypothesized that goldfish and common carp, which are known to hybridize, might be using relatively simple mixtures of common bodily metabolites to discern species identity and would, therefore, be attracted to each other but not distantly related species. However, we discovered that both of these species were only attracted to conspecific odours. Conspecific attraction was not influenced by immediate previous experience or accompanied by changes in feeding activity, suggesting it is pheromonally mediated. We hypothesize that carp and their relatives recognize each other using relatively complex mixtures of multiple classes of body metabolites. The pheromonal attractant used by common carp is of special interest because it could be used to attract and remove this species from North American waters where it is an invasive nuisance.