Elevations in gonadotrophin concentrations and milt volumes as a result of spawning behavior in the goldfish

In many male mammals and birds, exposure to sexual stimuli results in acute elevations of circulating luteinizing hormone (LH) and testosterone (T); a similar phenomemon has now been observed in the male goldfish (Carassius auratus). Mature males placed with either a receptive female or stimulus pairs of spawning goldfish had gonadotrophin (GtH) concentrations and expressible milt (sperm) volumes that were significantly greater than those of males kept in all-male groups. This stimulatory effect lasted from 20 min to at least 2 hr for GtH (20 degrees) and from less than or equal to 1 hr to greater than or equal to 24 hr for milt (14 degrees). When males were separated from the spawning pair by either a solid or perforated clear partition, no elevations of GtH or milt levels occurred. In contrast, these values increased in males placed in contact with a spawning pair, even when that pair contained no female, but a male induced to perform female sexual behavior by treatment with prostaglandin. These results suggest that, in goldfish, access to a spawning situation is necessary for rapid elevations in GtH and milt. Furthermore, it appears that the males must be sexually active in order for these physiological changes to occur, as males that failed to engage in courtship behavior with a spawning pair had GtH and milt values not different from isolated fish. This suggests that male sexual behavior and elevations in milt and GtH are concurrent events that share a common activation pathway in the brain. The increase in milt may be due to both neurally and hormonally mediated events that ensure milt availability for imminent spawning activity.