Evidence for the release of sex pheromones by male round gobies (Neogobius melanstomus)

Abstract

We report supporting evidence for the hypothesis that nesting round goby parental males release sex pheromones to attract females, and the results of preliminary experiments into pheromone isolation. We assessed pheromonal communication through physiological (electro-olfactogram, EOG) and behavioral responses of females to water conditioned by males. Reproductive (R) females responded with larger amplitude EOGs to water conditioned by (R) males compared with non-reproductive (NR) males. The R females reacted by directed movement to water conditioned by R males compared to untreated water, but not to water from NR males or females. We are isolating odorous compounds from this conditioned water by fractionating non-aqueous components, and testing for olfactory (EOG) potency. The R females showed strong EOG responses to a subset of HPLC fractions collected from water conditioned by R males, but not to NR male fractions; and the R male fractions were not stimulatory to N females. We have initiated identification of the pheromonal source through in-vitro incubation of testicular cells with tritiated substrates. Seven metabolites were formed from androstenedione in the testis. One of these (albeit in a low proportion) was recognized as etiocholanolone. However, the HPLC elution position with maximal EOG activity did not with the elution position of this steroid (and all but one of the unidentified metabolites). This preliminary study suggests that the round goby may use a steroidal compound(s), or metabolite(s) for reproductive pheromonal communication.