Our experiment was aimed at specifically testing the role of the conspecific alarm substance in eliciting a juvenile gape-limited morphology, so we used a heterospecific chemical alarm cue derived from the allopatric ostariophysan zebrafish Danio rerio as the control for a generalized response to an injured fish odorant. As such, we redicted fish exposed to zebrafish skin extract should not exhibit any morphological changes beyond those in the distilled water treatment.