Behavioural and electrophysiological responses by reproductive female Neogobius melanostomus to odours released by conspecific males

Behavioural and electrophysiological responses of reproductive and non-reproductive female round gobies Neogobius melanostomus to water previously occupied by male round gobies (reproductive male water) were compared. Reproductive females spent more time than non-reproductive females in a tank near the input of water conditioned from reproductive males. Also, reproductive females swam significantly faster than non-reproductive females, suggesting that reproductive male odour may have activated spawning behaviour. Olfactory epithelial field potential measurement (electro-olfactogram, EOG) showed that reproductive male water was a potent olfactory stimulus to reproductive females, but not to non-reproductive females. Reproductive females responded significantly more than non-reproductive females to solid-phase (octadecylsilane) extracts of reproductive male water. Also, when these extracts were separated on reverse phase high performance liquid chromatography (HPLC), reproductive females showed noticeably greater responses than non-reproductive females to the fractions that eluted between 30 and 40 min. The behavioural data support the hypothesis that reproductive male round gobies release compounds into the water that attract potential mates. The EOG data indicate that these compounds can be quantitatively extracted from the water and be partially purified by HPLC. The evidence is not sufficient to indicate whether or not the compounds are steroids. The relatively early elulion time on HPLC, however, suggests that if these compounds are steroids, then it is more likely that they will be conjugated rather than free steroids.