Urination and sound production during courtship behavior of male Japanese common rockfish Sebastes ventricosus
A research team led by Assistant Professor Takafumi Amagai, Research Fellow Yo Yamaguchi (JSPS PD Fellow), and Professor Kiyoshi Soyano at the Institute for East China Sea Research, Organization for Marine Science and Technology, Nagasaki University, has demonstrated for the first time in the world that male Japanese common rockfish (Sebastes ventricosus) court females using both urination and acoustic signals during the breeding season. The findings were published in the international journal Marine Ecology Progress Series on August 21, 2025.
This study provides the first visual and empirical confirmation that male S. ventricosus release urine toward the female’s snout during courtship.It was also confirmed that male S. ventricosus emit a distinctive vocalization during courtship. The released urine likely contains pheromones, suggesting that it signals to the female the male’s reproductive readiness. These findings overturn the long-held assumption that “marine fish produce little urine, making sexual pheromone transmission via urine impossible.”Furthermore, it was revealed that males with higher social status possess more developed bladders capable of storing larger volumes of urine. This finding also suggests a link between social status and reproductive success.
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.
Journal: Marine Ecology Progress Series
Volume & Pages: Vol. 767, pp. 121–135
Title: Urination and sound production during courtship behavior of male Japanese common rockfish Sebastes ventricosus
Authors: Takafumi Amagai, Yo Yamaguchi, Kiyoshi Soyano
Publication Date: August 21, 2025
DOI: https://doi.org/10.3354/meps14870
For more details, please see the full article published in Marine Ecology Progress Series.
