Living in a medium that can limit visual information but readily exposes the olfactory organ to hormonal compounds released by conspecifics, fish throughout their long evolutionary history have had both clear cause and ample opportunity to evolve olfactory responsiveness to these potentially important chemical cues (hormonal pheromones). Indeed, steroids, prostaglandins and their metabolites are reported to be hormonal pheromones in major fish taxa including carps (goldfish), catfishes, salmon and gobies. Best understood are goldfish, where periovulatory females sequentially release a preovulatory steroid pheromone and a postovulatory prostaglandin pheromone that dramatically affect male behaviour and physiology. Three major components of the preovulatory pheromone are the oocyte maturation-inducing steroid 17β,20β-dihydroxy-progesterone, a sulphated metabolite, and androstenedione, which together induce endocrine responses that increase the quantity and quality of releasable sperm and behavioural responses that enhance male spawning success. At ovulation, femles decrease release of the steroid pheromone, and increase synthesis of prostaglandin F_2α that acts internally as a hormone to induce female sex behaviour and externally as a pheromone triggering both endocrine and courtship responses in males. Hormonal pheromones not only challenge the classical concept that sex hormone actions are limited to reproductive synchrony within the individual but also provide examples where endocrine response to a hormonal pheromone could provide the basis for a pheromonally mediated endocrine feedback system involving at least two individuals and potentially many more. Given the conserved chemistry of fish endocrine systems and the evidence for similar hormonal pheromones among related fish, it is as yet unclear if or how hormonal pheromones are species specific.