Invasive male round gobies (Neogobius melanostomus) release pheromones in their urine to attract females

The round goby (Neogobius melanostomus) is an invasive fish in the Laurentian Great Lakes and beyond. Pheromones appear to be important for their reproductive success, as females are attracted to water in which reproductive males have resided ("conditioned water"). Previous investigation has shown conjugated and unconjugated forms of 3 alpha-hydroxy-5 beta-androstane-11,17-dione (11-oxo-etiocholanolone; 11-O-ETIO) are released in the urine of these males. The goal of this study was to determine if the urine of reproductive males and fractionated extracts attract females. We found that reproductively active females were attracted to male urine and to isolates of male-conditioned water that contained conjugated 11-O-ETIO. The fractionated preparation that corresponded to unconjugated 11-O-ETIO (i.e., "free" steroid released via the gills of males) was not attractive to reproductive females, but curiously, it was attractive to nonreproductive females. Olfactory sensory deprivation confirmed that the behavioural responses were mediated by olfaction. These findings take us closer towards identifying the pheromone(s) that attract female gobies and, therefore, closer to having a method to limit this species' damaging invasion.