Urination and sound production during courtship behavior of male Japanese common rockfish Sebastes ventricosus

Courtship behavior is of significant interest in the field of reproductive biology, particularly regarding ovoviviparous rockfish and fishery resources. Urination during courtship between male and female rockfish has been suspected, but no study to date has empirically demonstrated the occurrence of actual urination. In this study, we observed the urinating behavior of male Japanese common rockfish Sebastes ventricosus by dyeing the urine, allowing us to gain insight into the details of rockfish courtship behavior. Sounds recorded during trials in captivity suggested that rockfish males use their vocalizations to facilitate or help initiate the courtship process. Seasonal changes in the weights of the gonads and urinary bladder were observed. The amount of urine in males significantly increased during the reproductive season, whereas that of females remained stable at low levels. In addition, we found that males, particularly socially dominant individuals, developed a bladder and stored urine during the reproductive season, challenging the prevailing theory of osmoregulation that marine fish do not exchange pheromones through urine; instead, our study suggests that courtship urination plays an important role in transmitting olfactory signals that convey the reproductive status and social ranking of the male to the female. The results of this study further elucidate the mechanisms governing courtship behavior with pheromonal signals and urine retention in marine teleost species.