Reproductive seasonality of Monetaria annulus (Linnaeus, 1758) (Mollusca: Gastropoda: Cypraeidae) in a temperate area

Abstract

The objectives of this study are: (1) to detect the developmental stages in the gonads of Monetaria annulus through histological analysis; (2) to determine the spawning season of this species in a temperate area through seasonal changes in the proportion of each gonadal stage; and (3) to analyse the sex ratio and sexual dimorphism through gonad histology. Samples were obtained randomly from an intertidal rocky shore in Hanazesaki, Ibusuki, Kagoshima Prefecture, Japan (31 11′30.10^″N, 130 30′29.70^″E) every 2 months from February 2011 to June 2012. Reproductive stages were identified and classified as Stage 1 (initial maturity), Stage 2 (peak maturity) and Stage 3 (spawned). Stage 2 males and females were found during more than half of the year, but their proportion varied seasonally. Although the reproductive peak was slightly different year by year in the temperate area, M. annulus seemed to have two reproductive seasons, in spring and from late summer to winter. The sex ratio was biased towards females, but it was not statistically significant. The mean shell length of females was significantly larger than that of males, though they overlapped widely.

Keywords:

• histological analysis
• reproductive stages
• sex ratio
• sexual dimorphism

Acknowledgements

The authors thank the undergraduate and post-graduate students of the Faculty of Fisheries, Kagoshima University, for their assistance in collecting the samples. We thank Professor Yasuji Masuda, Professor Tadahide Noro, Professor Hiroshi Suzuki (Faculty of Fisheries, Kagoshima University) and Professor Kei Kawai (Research Center for the Pacific Islands, Kagoshima University) for their valuable advice and support with laboratory facilities. Special thanks are due to Kagoshima Prefectural Fisheries Technology and Development Center for permission to use their sea temperature data. We appreciate the reviewers and editor of Molluscan Research for their useful comments, which helped us improve our paper. This study was made possible through the support of a Japan MEXT Scholarship.