Male zebrafish (Danio rerio) odorants attract females and induce spawning

In zebrafish, the chemical identity and biological roles of reproductive pheromones have yet to be clarified. The current study assessed the role(s) of male-released odorants in a reproductive context, and evaluated the possible involvement of steroids and their metabolites. Females were placed in chemical and/or visual contact with males. In chemical contact, females ovulated as frequently whether they could see the males or not. Conversely, females with visual contact alone with males ovulated as frequently as isolated females. Male-released odorants attracted females; visual contact with males attracted females, but to a lesser extent; the two effects were additive. The olfactory potency of solid-phase extraction of male- and female-conditioned water was assessed by the electro-olfactogram; males released more potent odorants than females, but the most potent extract came from water in which males and females interacted freely. HPLC fractionation of these extracts revealed that, while in all samples some fractions contained odorants, male-specific activity was contained in the first four fractions, suggesting that the compounds involved are relatively hydrophilic. Finally, the olfactory potency of some steroids, previously suggested to have a pheromonal role, was assessed. However, it is unlikely that these steroids contribute significantly to the odor of fish-conditioned water.