ASPECTS OF REPRODUCTION AND TRIPLOIDY MANIPULATION IN THE PEARL OYSTER, PINCTADA RADIATA (LEACH)

Abstract

Abstract : Pinctada radiata spawns in summer/autumn, but minor out-of-season spawning may take place. Young oysters mature at 0.6–1.25 mm heel depth (HD) or 15–20 mm dorsoventral measurement (DVM), which corresponds to an age of 3.5–7 months. A standard pearl oyster of 50 mm hinge length (HL) showed more convincing results of seasonal changes in weight than other standardized shell dimensions. Seasonal changes in weight are clearly related to the spawning cycle and recovery exhibited by the oysters. Most relationships between dimensions and weight studied here showed negative allometry in adults, but isometry was more common in young oysters. The structure of the biofouling community was basically simple in nature and consisted of nine associated species, of which the bryozoan, Bugula sp., and the alga, Hormophysa triquetra, were dominant. Bucephalus sp was found parasitizing and destroying the adult gonad of 4% of the pearl oysters sampled. There was no indication of seasonality in the appearance of the parasite nor any trend in the size of infected pearl oysters. No relationship was found between the occurrence of pearls and the infection with Polydora, the tube-boring polychaete worm. Natural pearls were very rare (1.93%) in the samples analyzed and were of small ( However, in Experiment 2, meiosis II culture showed a significant increase in anteroposterior measurement (APM) and dorsoventral measurement (DVM) over both meiosis I and the controls from week 1 to week 4. In week 5, there was no significant difference in the size of larvae among the three cultures. It is proposed that the overall percentage of triploids produced in meiosis II culture accounted for the significant difference in weeks 1 to 4