Tropical monsoon environments and the reproductive cycle of the orange-spotted spinefoot Siganus guttatus

Abstract

Negligible fluctuation in water temperature and photoperiod may cause fish species in tropical environments to utilize additional environmental factors to initiate reproductive activities during suitable periods of the year. We examined periodic changes in ovarian development of orange-spotted spinefoot (Siganus guttatus) in coral reefs off Karimunjawa Archipelago, Indonesia, and compared them with changes in regional environmental factors. The gonadosomatic index of this species increased initially during March–May and again during September–November. Concomitant with the increase, yolk-laden oocytes were observed (histologically) in ovaries, suggesting that the ovary develops twice a year. Initiation of reproductive activities was consistent with transition periods between rainy and dry seasons, suggesting that environmental cues linked to tropical monsoons influence reproductive activity. This suggestion is inconsistent with previous findings for the same species, but in higher latitudes, that the initiation of reproductive activity was influenced by increases in photoperiod and water temperature. It was observed that spinefoot exhibit plasticity in the use of environmental factors within habitats. Synchronized spawning occurred twice during the reproductive season, and was repeated between the new and first quarter of the lunar cycle. This periodicity was consistent with the spawning rhythm in other regions, suggesting that this species may perceive cues from the moon to synchronize spawning.

Keywords:

• Indonesia
• lunar cycle
• reproductive cycle
• spinefoot
• tropical monsoon

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

This study was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science, and in part by the 21st Century Center of Excellence Program of the University of the Ryukyus from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This contribution is from the Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Okinawa, Japan.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark