Age and growth of Neptunea arthritica estimated from growth marks in the operculum

Abstract

The age and growth of the whelk, Neptunea arthritica, was estimated based on growth striae on the operculum. Individual whelks were sexed and divided into normal and abnormal groups, based on the presence of imposex and parasite infection. The monthly marginal growth was used to determine the annual growth mark formation on the operculum. The whelk's sex (male and female), condition (normal and abnormal) and size (mature and immature) were evaluated as factors that can affect the marginal growth. Only in normal females did size affect the marginal growth, suggesting that parasite infection and imposex were not a biasing factor in the age estimation. Significant differences between low and high monthly marginal growth in normal males were found. Between operculum length and shell length and total body weight a positive relationship was found, while the same trend was observed in all female groups as well as abnormal males, but differences were not significant. The same relationship was observed between the number of stria with shell length and total body weight in all groups. The results suggest that opercula striae could be used to age N. arthritica. The Gompertz equation was the best curve that fitted the data for growth in normal groups, based on Akaike's information criteria, and it was used for all groups. The age at first sexual maturity was estimated for normal males and females to be 4.6 and 6.1 years, respectively.

Keywords:

• Age
• growth
• imposex
• Neptunea arthritica
• operculum
• parasite infection

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

We thank Mr Kimihiko Maekawa and the Aquaculture Cooperative of Lake Saroma for their valuable support in this work. We also would like to thank Prof. Seiji Goshima, Prof. John Bower, Dr Sachindra Nakkarike and Roberto Lombardo for their help with the improvement of this manuscript. Special thanks to reviewers for their valuable comments and suggestions.

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