Researchers at the University of Minnesota have demonstrated that goldfish can advertise their reproductive condition through pheromones released in their urine.
Christopher Applet and Peter Sorensen found that female goldfish would increase the rate and quantity of urinary pheromone release as they came into breeding condition.
Goldfish eggs are viable for only a few hours following ovulation, and so it is important that the female is able to attract a male within this time period, and the authors believe that the fish use urinary pheromones to advertise their readiness to mate.
The research further demonstrated that the frequency of the hormone release would increase when the females were positioned by a suitable spawning site, in order to attract males over to their selected site.
Goldfish ranging in size from 13 to 39 grams were used in the experiments, fed on flaked foods. The tests included placing the sexually receptive females in with sexually responsive males, unresponsive males, females or no fish, to see the effect on urine release rates.
The urine, and consequently pheromone, release was greatest when the sexually responsive males were introduced. It was lowest when other females, or no fish at all, were added in with the sexually receptive females.
Further experiments tested the response of the male goldfish to the introduction of the pheromone hormone. The males were placed in a large maze containing patches of vegetation. Swimming speed and inspections of vegetation both greatly increased upon the addition of the pheromone, with their particular focus on the vegetation into which the pheromones were introduced.
For more information, see the paper: Applet, CW and PW Sorensen (2007) - Female goldfish signal spawning readiness by altering when and where they release a urinary pheromone. Animal Behaviour, vol. 74, issue 5. pp. 1329-1338.