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Abstract
The present study compares the ability of conventional condition indices (based on weight of the whole organism, weight of its flesh, and/or its shell weight) and visual quantitative indices (based on measures of the digestive gland, gonad, and capsule gland on digitized images of sections of these organs) for the assessment of reproductive activity in Hexaplex trunculus. To estimate conventional indices, a total of 120 standard-sized specimens (50 males and 70 females) in the 60–70 mm shell length interval were analysed. To estimate visual quantitative indices, a total of 903 specimens (501 males and 402 females) were analysed for the gonadosomatic index (GSI); females were also analysed for the capsule gland index (CGI). Compared to conventional indices, the visual quantitative indices (GSI and CGI) followed seasonal variations of the species reproductive cycle and identified broad changes in reproductive development (being highly accurate in detecting the main period of gonad maturation and spawning that occurred between May and June). Results indicate that both GSI and CGI constitute simple, practical and efficient indices for the routine assessment of reproductive activity in H. trunculus, providing a useful and reliable alternative to conventional condition indices and to histological analyses. Results of this study encourage the use of similar sampling procedures and analytical techniques, and analogous visual quantitative indices, to assess reproductive activity in other gastropod species.
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
The authors would like to thank the technical staff of IPIMAR for their help with laboratory sampling procedures. Thanks are also due to the editors and two anonymous referees for valuable comments and suggestions, and to Margaret McBride for the thorough revision of the English language, which altogether greatly improved the final version of the manuscript. This study was partially funded by a PhD grant from the Fundação para a Ciência e Tecnologia (FCT: SFRH/BD/5139/2001) and by the research project PROMAR (Interreg III-A).
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