Research News

Continuous 24-hour observations clarify time these fish engage in courtship, spawning

Late-night activity

Infrared camera footage shows medaka fish spawning at midnight.

Credit: Osaka Metropolitan University

Osaka Metropolitan University researchers have gained clearer insights into the natural behavior of medaka, small fish that are useful as model organisms in the lab.

Specially Appointed Dr. Yuki Kondo and Professor Satoshi Awata of the Graduate School of Science conducted continuous 24-hour observations of medaka raised in an environment close to their natural habitat and verified when the fish begin their reproductive behavior.

Medaka spawning behavior in a natural environment begins around 1 a.m. and peaks between 2 a.m. and 4 a.m. In addition, courtship behavior was frequently observed between 2 a.m. and 5 a.m. Many other behaviors also started during the late-night hours.

“These discoveries will lead to a review of the experimental conditions for medaka as a model organism and demonstrate the importance of information on the natural ecology of such organisms,” stated Dr. Kondo.

Funding

This study was funded by the Japan Society for the Promotion of Science (JSPS) KAKENHI (22K20666 to Y.K. and 23H03868 to S.A.), the Sasakawa Scientific Research Grant from the Japan Science Society (2023–5013 and 2024–5010 to Y.K.), and the Tokyo Zoological Park Society Wildlife Conservation Fund (to Y.K.).

Paper information

Journal: Scientific Reports
Title: Courtship and spawning behaviour of medaka in a semi-outdoor environment initiating at midnight
DOI: 10.1038/s41598-025-01037-8
Authors:  Yuki Kondo, Satoshi Awata
Published: 16 May 2025
URL: https://doi.org/10.1038/s41598-025-01037-8

Reference

Nighthawks: Wild medaka actively court female fish in wee hours

Contact

Graduate School of Science
Yuki Kondo
Email: youkikondou[at]omu.ac.jp

Satoshi Awata
Email: sa-awata[at]omu.ac.jp

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