Coastal Aquaculture and Mariculture (2+1)

Unit 7 - Culture of Molluscs and Seaweeds

7.3.1. Biology

• Pinctada fucata is commonly used for pearl production because it produces fine pearls. In nature it is found attached to hard substratum by means of byssus threads. It is stenohaline although it survives short term salinity fluctuations. It is a filter feeder, feeds mainly on phytoplankton, occasionally on bivalve eggs and copepods.
• Life span is 5-6 years, maximum size 10cm. Annual growth rate is about 50mm. environmental factors such as depth, transparency, temperature, salinity, currents, calcium content of water, food and foulers influence growth rates.
• Sexes are separate; however, hermaphroditism and change of sexes from one spawning season to another are not uncommon. It attains maturity at a size of 25-30mm. Has two peak spawning seasons, one during July to August, another from November to December. Individual oysters spawn more than once in spawning seasons.
• Eggs and sperms are shed in water, fertilization is external. Hatching takes place in about 4 hours. Spat settle when 0.3mm in size.
• Spat availability in the wild fluctuates, hence hatchery produced spat are used for culture.

Development of pearl
Natural pearl is formed when a foreign material enters the body of pearl oysters. Epithelial layer of mantle forms a sac around the foreign body which secretes nacre over the nucleus (foreign body) layer after layer resulting in pearl formation. Shape of the pearl depends on the shape of the nucleus/foreign body. Nucleus/nuclei can be implanted along with a piece of mantle tissue as graft into the gonads oysters which results in formation of cultured pearls.