Hormonal pheromones in fish

Fish commonly exhibit reproductive responses to waterborne steroids, prostaglandins (PGs), and their metabolites (hormonal pheromones) - a logical result of a long evolutionary history spent in a medium that often reduces visual information but readily exposes the olfactory organ to information-rich chemicals released by conspecifics. Although fish from major taxa, including carps, catfishes, salmon, and gobies, respond with great sensitivity and specificity to a variety of hormonal pheromones, in no species are hormonal pheromones well understood. The phenomenon appears best characterized in goldfish, where steroid and PG pheromones released sequentially by periovulatory females dramatically affect male behavior, physiology, and reproductive fitness. Goldfish steroidal pheromones appear to involve only specializations of the receiving individual, a situation which these authors have termed chemical spying, whereas in other fish, where the sending individual is also specialized, hormonal pheromones evidently function in true communication. By demonstrating that sex steroids and PGs synchronize reproductive functions not only by endogenous hormonal actions but also by exogenous pheromonal actions, the relatively recent discovery of hormonal pheromones has considerably expanded our concepts of fish reproductive function while providing valuable model systems for future study of olfactory function and pheromone evolution. © 2009 Elsevier Inc. All rights reserved.