Katsuaki Fujinaga, Anthony S. Ilano, Hirotaka Nomura, Richard T. Miranda, Shigeru Nakao
The state of imposex in Neptunea arthritica from seven sites along the coast of Hokkaido, Japan was examined in 2002 based on the criteria: (i) relative penis size index (RPSI); (ii) imposex frequency; (iii) stage frequency distribution of imposex in adult and immature whelks; and (iv) sex ratio. RPSI differed from site to site, although values from all sites were low (0.186-5.294). In particular, the RPSI values for four sites were very low (<1.0). In sites where immature whelks were also collected, the frequency of imposex was considerably lower in immature (7.7%-55.6%) than in adult whelks (50%-95.2%) except at one site. The imposex stage frequency distribution also differed among sites, and the trend in the adult whelks corresponded with their RPSI value. Female whelks showing severe imposex (Stage 3 and 3+) were restricted to large individuals. © 2006 Blackwell Science Asia Pty Ltd.
Faculty of Social Welfare, Dohto University, Kitahiroshima, Hokkaido 061-1196, 149 Nakanosawa, Japan; Biology Department, University of San Carlos, Technological Center, 6000 Cebu City, Philippines; Central Laboratory, Marine Ecology Research Institute, Chiba 299-5105, 300 Iwawada, Onjyuku-machi, Japan; Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 3-1-1, Minato-cho, Japan
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