RELATIONSHIPS BETWEEN SHELL MORPHOLOGICAL TRAITS AND THE BYSSUS DIMENSIONS IN THE WINGED PEARL OYSTER PTERIA PENGUIN (RODING, 1798) CULTIVATED IN SANYA, HAINAN ISLAND, CHINA

The relationships of the shell morphological traits, including the byssus dimensions, were recorded and analyzed in sample groups of 18- and 30-mo-old cultured winged pearl oysters, Pteria penguin. All relationships among shell dimensional traits with respect to shell height (SH) in the 18- and 30-mo-old oysters were observed to be positive and significant (P < 0.05). Although allometric growth was observed in both groups, the r(2) values in the relationship between SH and total wet weight (TW) were higher in old oysters than in young ones. These findings indicate that weight in young oysters is heterogeneous. Moreover, the TW-SH ratio showed a clearer tendency to increase relative to exterior dimensions in old oysters. The r(2) values in the correlation between SH and maximum dorso-ventral length were the highest in both oyster groups; hence, this dimension is a reliable predictor of SH. On the other hand, the relationships between SH and either hinge length or shell thickness were slightly weak in both age groups. Oysters with no byssus were found only in the younger group. It is possible that older oysters are less susceptible to factors that induce byssus shedding. In young oysters, the length and diameter of the byssus was closely related to the weight of the animal rather than the size of the shell. But, as individuals continued gaining weight, no augmentation in the byssus organ diameter was measured, suggesting a threshold for the byssus diameter in heavier oysters. Because it is possible that byssus size may influence the quality of pearls formed in the oyster due to the proximity of the pearl sac to the byssus root, it is important to consider the weight of the oysters selected or cultivated for pearl production, as this may indirectly affect the quality of the finished pearl product.