The maturity and breeding season of the bellybarred pipefish, Hippichthys spicifer, in Okinawa-jima Island rivers
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We investigated the breeding season and size at maturation and described the morphology of newly released Hippichthys spicifer larvae collected from the estuaries of four rivers on northern Okinawa-jima Island, southern Japan. The minimum size of brooding males was 108 mm standard length (SL). The smallest mature female, as estimated from gonadosomatic index (GSI) analysis and histological observations of gonads, was about 100 mm SL. Histological observations showed the gonad of H. spicifer to be a cylindrical tube with a sequential pattern of follicle development and a single germinal ridge. We surmised that the breeding season is year-round, as shown by monthly changes in female GSI, gonad histology, and monthly changes in the occurrence of brooding males. The monthly changes in female GSI and proportions of brooding males were small in winter. The number of eggs in the male brood pouch ranged from 114 to 1,764 (604.4 ± 322.8, mean ± standard deviation; n = 25). The SL of the released larvae was 9.9 mm. All fins except the pectoral fins were formed, the body was elongated, and the developmental stage was similar to that of other Urophori species. The smallest individual present in the mangrove areas of estuaries was 78.0 mm SL.
KeywordsBreeding season Estuary Hippichthys spicifer Larva
The authors are grateful to Emeritus Professors S. Shokita and K. Takano, Associate Professor T. Yoshino, and Assistant Professor H. Shikatani, Faculty of Sciences, University of the Ryukyus, for their kind support, and K. Maeda, Y. Mizuno, and W. Noda for valuable information. We thank the members of the Laboratory of Fisheries Biology & Coral Reef Studies, Faculty of Sciences, University of the Ryukyus, and those of the University of the Ryukyus Diving Club for help with fish collection and information. The authors also thank Associate Professor J.D. Reimer (Rising Star Tenure Track Program, University of the Ryukyus) for critical comments on the manuscript and great help with the English. This study was partially supported by the 21st Century COE program of the University of the Ryukyus.
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