Female goldfish signal spawning readiness by altering when and where they release a urinary pheromone

Although it is established that many species of fish release hormonally derived sex pheromones in their urine, whether these cues are unspecialized metabolic by-products or specialized communicatory signals is not known. Here, we addressed this question in the goldfish, Carassius auratus (a leading model of hormonal sex pheromone function) by conducting two experiments. We first monitored urine release by sexually receptive females that were placed with a sexually active male, an inactive male, another female, or no other fish. Sexual receptivity was induced using prostaglandin F2α, a hormone also known to evoke release of 15-keto prostaglandin F2α (15K-PGF2α), a potent urinary pheromone. We found that sexually receptive females increased the frequency with which they urinated when placed with males (regardless of male sexual activity) but not females. Furthermore, females showed a strong tendency to urinate when rising into spawning substrate, suggesting they might be using urine as an attractive lure. This hypothesis was confirmed by a second experiment, which found that 15K-PGF2α attracted males to specific locations. We conclude that goldfish, and likely many other fish, control the release of urinary prostaglandin pheromones to advertise their condition and location, perhaps exemplifying an early step in the evolution of a chemical communication system.