“…Calcein used as a CaCO 3 -stainer was successful by immersion as a method for age validation producing a concise bright lime-green (Riascos et al, 2007), Donax hanleyanus (Herrmann et al, 2009), Cerastoderma edule (Mahé, Bellamy, Lartaud, & de Rafelis, 2010), Pinctada margaritifera (Linard et al, 2011), Loripes lacteus (van der Geest, van Gils, van der Meer, Olff, & Piersma, 2011) and other bivalves (Rowley & Mackinnon, 1995 Regarding the calcein concentration impact on marking, our individuals produced better marking (100%) at the lower (0.4g/L) than higher concentration (73% for 0.7g/L), as well as, a better quality mark at the lesser concentration (more perfect and good marks). The 27% of oysters at the greater concentration that showed no marking, actually showed green fluorescence over the whole shell thickness, as if the greater concentration affected the complete aragonite layer.…”