A Near-Round Natural Pearl Discovered in the Edible Oyster Magallana bilineata
Pakistan, which has a coastline stretching 1,046 km (650 miles) along the Arabian Sea, the Indian Ocean, and the Gulf of Oman, is blessed with numerous marine resources, including oysters that mainly inhabit estuaries and mangrove habitats. In Sindh Province, some oyster reefs at Hab River Delta have high ecological and economic value. Nine edible oyster species belonging to the genera Crassostrea, Saccostrea, and Ostrea have been recognized from different localities there. Pearl-forming mollusks belonging to the genera Pinctada have been reported from Daran Beach.
The Ostreidae family includes edible oysters and is most commonly known as a source of seafood (K. Scarratt et al., “A note on a pearl attached to the interior of Crassostrea virginica [Gmelin, 1791] (an edible oyster, common names, American or Eastern oyster),” Journal of Gemmology, Vol. 30, No. 1-2, 2006, pp. 43–50). Of these, Magallana bilineata has the widest distribution in the Indo-Pacific region, encompassing the coasts of northern Arabia, the Bay of Bengal, the Andaman Sea, the Java Sea, South China and Vietnam, the Philippines, and Okinawa.
Magallana bilineata is a euryhaline species that inhabits backwaters, creeks, estuary banks, coastal bays, and lagoons, forming oyster beds on a large scale. A large number of specimens of this species from Hab River Delta were examined to study the taxonomic characteristics of the genus Magallana as part of a joint project between Japan and Pakistan. Ten shells of each species were opened. Only one shell of M. bilineata (150 mm shell height) contained a pearl, attached to tissues near the adductor muscle. It was near-round, with a smooth surface and a purplish and off-white color very similar to the inner shell layer of M. bilineata (see above, left). The crystal structure of calcium carbonate was observed under high magnification. The non-nacreous, shiny pearl (see above, right) was 4.15 mm in diameter and weighed 0.02 g. The specimen is housed at the Centre of Excellence in Marine Biology, University of Karachi (part of the study collection of author SA).
Oysters living in tropical and warm regions have darker, more vivid, and more extensive coloration than those in cooler climates. Our finding is very similar to that of Scarratt et al. (2006), which found a pearl inside Crassostrea virginica that was attached to an adductor scar. In our case, the pearl was attached to the tissues near an adductor scar. This finding demonstrates the very rare phenomenon of edible oysters producing natural pearls. However, further work will be needed to determine its chemical composition using highly accurate analytical methods.
