Kanika Kanjanachatree, Kanoktorn Piyathamrongrut, and Nikorn Inthonjaroen

pp. 659 - 671

Abstract

Environmental aspects and biology of pearl oysters are the important conditions affecting pearl
production. In order to obtain commercially valuable pearl from winged pearl oysters, Pteria penguin, three
sizes (shell-length) of the oysters: small (130-135 mm), medium (160-165 mm) and large (185-200 mm) were
suspended at 2 m (surface), 5 m (mid-depth) and 8 m (bottom) below the sea surface from February to
November, 2001. Using a factorial design, the data were randomly recorded by month. All sizes of the pearl
oysters at the surface produced pearl of significantly greater thickness than those at the greater depths. The
small-sized pearl oysters at the surface depth produced the thickest pearl (0.612 mm.) which took only 7
months for harvesting, and the pearl thickness was correlated with growth response in shell length. In contrast to the growth rate in tissue weight and mortality rates which were 36.00, 26.00, 24.00% at the surface depth; 30.60, 24.60, 16.00% at mid-depth and 25.30, 19.30, 12.00% at the bottom for the small, medium and
large-sized oysters, respectively. The results depended on infestation of fouling organisms on oyster shells
which were much more intense at the surface than at a greater depths and slowed the growth rate in tissue
weight, especially in the small-sized oysters. However, there was a greater amount of many kinds of plankton,
the food resource of marine animals, at surface than at greater depths, so it retained shell-length growth and
pearl production of the small-sized oysters: The other environmental factors, such as salinity, dissolved
oxygen, pH and sea water temperature, at all depths did not have an impact on the pearl oyster rearing.