Marking the shells of juvenile and adult eastern oysters, Crassostrea virginica, with the fluorochrome dye calcein and measuring growth and mortality after marking

Abstract

ABSTRACT Techniques for positive re-identification of finfish are well developed and are used to estimate vital rates, migration patterns and stock structure. Fluorochrome dyes, like nontoxic calcein, have been used with success to mark hard parts of fish and the shells of some molluscs. Yet, despite the commercial and ecological importance of the eastern oyster Crassostrea virginica, a systematic evaluation of the effectiveness of calcein for marking this species does not exist. In this study, methods that have been used for marking freshwater mussels with calcein were tested on 2-week- and 2-month-old juvenile C. virginica and on 3-year-old adult C. virginica. Individuals were immersed in 250 mg l−1 of calcein for 24 h either once (single treatment) or three times (triple treatment), and then observed to determine whether marks were visible, how long they remained visible and whether calcein influenced growth and mortality of the different age classes. Results indicated that all marked individuals were recognizable under blue light, that multiple distinct marks were possible on juveniles and that marks on juveniles could remain visible for 3.75 years. Growth of juveniles and adults treated with calcein was not significantly different from controls after 11 months. Survivorship did not differ between treated and control individuals for all treatments and ages, except the 2-month-old juvenile oysters that were immersed three times. Results indicate that calcein is an effective and safe marking technique for juvenile oysters from robust cohorts, and could be used to enhance studies of growth, mortality, larval transport and settlement in situ.