Calcein staining of calcified structures in pearl oyster Pinctada margaritifera and the effect of food resource level on shell growth

Marine mollusc shell growth has been widely measured using fluorochrome marking. In order to test the efficiency and reliability of calcein staining on Pinctada margaritifera shells and pearls, the present study examined two administration methods, different concentrations and several immersion times. Immersion in a 150 mg L−1 calcein solution for 12 h to 24 h appeared to be the best method for marking P. margaritifera shells. For pearl marking, injection of a 200 mg L−1 calcein solution into the pearl pouch was the optimal method. Calcein marking was then used to measure the influence of food resource levels on the shell growth. Groups of 23-month-old P. margaritifera were fed at three trophic levels for two months. The two highest food levels tested (6000 cell mL−1 and 15 000 cell mL−1) induced uniform growth between the dorsal and ventral sides of shell, whereas the lowest food level (800 cell mL−1) induced greater growth on the dorsal side. Shell deposits from the ventral side were observed using a scanning electron microscope, revealing that the difference of the trophic level over two months had modified the thickness of the aragonite tablets formed. These results showed that the trophic level is a major factor conditioning P. margaritifera development.