[Topics] A research team led by Professor Norio Onikura has successfully documented the spawning behavior of the Hakata-sujishima loach (Cobitis sp.) under captive conditions

Previously undocumented sex-specific behaviors have been elucidated

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A research team comprising Ms. Kanna Nagae, a third-year doctoral student at the Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, and Professor Norio Onikura of the Faculty of Agriculture, has successfully induced spawning and recorded the reproductive behavior of the Hakata-sujishima loach (Cobitis sp.) under captive conditions. This subspecies is endemic to Kyushu and is found exclusively in rivers flowing into Hakata Bay.The Hakata-sujishima loach was designated as a Nationally Rare Wild Species under the Act on Conservation of Endangered Species of Wild Fauna and Flora by the Ministry of the Environment in February 2019, and as a Fukuoka Prefecture Designated Rare Species in April 2021. Currently, it is being preserved through captive breeding at Marine World Uminonakamichi.Although hormone-induced spawning under captive conditions has previously been conducted at Marine World, this study marks the first successful video documentation of the entire spawning behavior sequence.

By utilizing red LED lighting, which is less likely to disturb fish, the research team was able to record nocturnal spawning behavior. While the spawning behavior itself was largely consistent with that observed in closely related Cobitis species, the study documented an unusually high frequency of spawning events--17 occurrences over a three-hour period involving one to two pairs, with egg and sperm release confirmed in 13 of those events.Notably, the duration from the male wrapping around the female to the completion of gamete release and separation was less than two seconds. Approximately 1,000 fertilized eggs were ultimately obtained. These findings, derived from detailed video analysis, provide ecologically intriguing and conservation-relevant insights.The full report is published in the Japanese open-access journal Ichthy, Volume 57, pages 8-14.

This spawning experiment was conducted as part of a research project funded by the Environmental Research and Technology Development Fund (JPMEERF20254003) of the Ministry of the Environment and the Environmental Restoration and Conservation Agency of Japan. The offspring obtained from this study will be provided to Professor Kohei Ohta, Professor Tomoyuki Kokita, and Assistant Professor Chakraborty Tapas of the Faculty of Agriculture, Kyushu University, who are collaborating on this research. These individuals will be utilized for further research and development, including germline stem cell-based lineage preservation and assessments of genetic integrity in rare fish species.Currently, only two rivers are known to host populations of this subspecies. However, the individuals bred at Kyushu University in this study originate from a river distinct from that of the lineage preserved at Marine World Uminonakamichi. This achievement contributes to ex situ conservation efforts by maintaining multiple genetic lineages of this rare species.

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Researcher's Comment

Our research team is also engaged in lineage preservation of Acheilognathus tabira tabira, another species designated under the Act on Conservation of Endangered Species of Wild Fauna and Flora. However, lineage preservation requires substantial time and effort, and repeated captive breeding may pose risks of genetic degradation.We hope that the individuals obtained through this recent spawning experiment will grow successfully and serve as valuable research material for advancing technological innovations aimed at more efficient lineage preservation.

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For Research-related inquiries

Norio Onikura, Professor
TEL: 0940-52-0163
FAX: 0940-52-0190
Mail: onikura★agr.kyushu-u.ac.jp
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