Shellfish Breeding and Hatchery Management (2+1)

21.2.1 Development of Pearl oyster (Pinctada fucata)

The Indian pearl oyster. Pinctada fucata inhabits in the sea bottom. The male and female oysters spawn and discharge the gametes. The eggs are fertilized and assume spherical shape . The fertilized egg measures few microns and the first & second polar bodies will be released.

The first cell division lakes place 45 min after fertilization. Repeated cell divisions result in the morular stage in 3-4 hrs. The morula looks like a ball with cells.

The morula, after development will attain the plastula and gatrula stages. The trochophore stage is reached in 10 hrs. The trochophore larva has preoral and postoral cilia with a single filagellum. In 20-22 hrs after fertilization, the trochophore develops into veriger larva with the formation of shell, stright hinge, mantle and velum. It is also called strigh hinge larva or 'D' shape larva and measures 67.5 um in anteroposterior axis and 52.2 um in dorsoventral axis. From D - shape stage onwards algal food is given.

On 10^th to 12^th day the veliger reaches the umbo stage with the formation of Umbo. It measures 135x130um. The umbo larva transforms into eyed larva with the development of eye spot at the base. At this stage, the larva measures 180x170um.

On 18^th day, pediveliger stage is reached with the development of functional foot. The foot helps in movement and also in temporary adherence to objects. At this stage, the velum disappears. The plantigrade stage is reached on 20^th day and it measures 220x200 um. Byssus threads are produced for attachment. The plantigrade metamorphoses by the formation of stright hinge line and anterior and posterior ears. Byssus notch is well developed. It measures 300um and resembles the adult pearl oyster in appearance.