Journal of Ethology

, Volume 37, Issue 2, pp 175–186 | Cite as

Dual social structures in harem-like colony groups of the coral-dwelling damselfish Dascyllus reticulatus depending on body size and sheltering coral structures

  • Rei SakanoueEmail author
  • Yoichi Sakai


The coral-dwelling damselfish Dascyllus reticulatus shows heterosexual cohabitation on branching corals and has been considered to maintain a haremic mating system, where a few males monopolize mating within the group. However, details of the group structure have not been investigated. To clarify the individual-level group structure of D. reticulatus, we conducted field observational surveys on a damselfish population on reefs of Kuchierabu-jima Island, southern Japan. Relatively large D. reticulatus inhabited corals with long branches and wide gaps with a female-biased sex ratio, and they maintained haremic groups where the largest male monopolized mating. In contrast, small adults and juveniles cohabited in higher individual densities on short-branch corals, with no bias in individual sex ratio. Only nine of 26 adult males in the short-branch coral groups showed mating activities. Nineteen of 37 adult females in the short-branch coral groups spawned, and their spawning frequency was lower than that of the females on the long-branch coral. Thus, we observed two contrasting social compositions and mating activities within harem-like cohabitation groups that depended on body size and sheltering coral structures. We observed inter-harem moves by large non-breeding individuals from the short-branch corals to the long-branch corals, implying a conditional use of the two types of groups related to body size. Our observations present a new example of multiple forms of groups in haremic reef fishes.


Harem polygyny Body size Spawning frequency Branching corals Dascyllus reticulatus Field observation 



We thank the people of Kuchierabu-jima Island for allowing the field survey. Dr. H. Hashimoto, Dr. T. Tomiyama, Dr. Y. Kimura, and colleagues at the laboratory of Biology of Aquatic Resources, Hiroshima University, are thanked for their helpful support of this study. We are grateful to Dr. T. Fujii (Kagoshima University) and Mr. T. Shimada (Japanese Society for Coral Taxonomy) for kind support in taxonomic identification of coral species. We would like to thank Editage ( for English language editing. This study was supported by grants from JSPS KAKENHI (Grant Numbers 24570027, 15K07222 and 18K06419) and the Sasakawa Scientific Research Grant from The Japan Science Society.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

Ethical approval

All procedures performed in the present study were in accordance with the guidelines for proper conduct of animal experiments and related activities by Hiroshima University (ID: A170410) and the guidelines for ethological studies by the Japan Ethological Society.


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Copyright information

© Japan Ethological Society 2019

Authors and Affiliations

  1. 1.Graduate School of Biosphere ScienceHiroshima UniversityHigashi-HiroshimaJapan

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