Marine Biology (2+1)

Crassostrea madrasensis

Species: Crassostrea madrasensis

Family : Ostreidae

Common Name : The Indian backwater oyster / the edible oyster

Habitat : Brackish and shallow coastal waters

The shape of the shell of C. madrasensis is very irregular. Marginal denticles (teeth ) absent. The adductor muscle scar single, kidney shaped (with the ventral edge pointed and the dorsal edge truncated), dark purple and sub centrally (anteriorly) placed. The external surface of the shell valves are laminated like overlapping leaves and distinct around the posterior margin of the shell. The attachment is by the lower half of the cup shaped left valve. The right valve is flat or slightly concave. Hinge is narrow, elongated and toothless.

It has been observed that the shape of C. madrasensis varies in relation to the substrate on which it settles and grows. Those settling on rock surfaces are round, those growing on soft mud are elongated and narrow and on uneven surfaces it conforms to that of the substratum. Over crowding results in highly irregular forms.

This is a euryhaline species found in dense populations as thick beds in estuaries, backwaters, lagoons, coastal bays and rarely in the open coastal waters. They also colonize muddy bottoms and thrive successfully in all maritime states in India, Tamil Nadu has the richest population of C. madrasensis.

Sexes are separate and the gametes are discharged to the estuaries. Breeds throughout the year with intensive spawning during April, May and August – September.

Feeds largely on organic detritus and phytoplankton and the growth of this oyster varies from place to place depending upon the availability of food and the environmental conditions. C. madrasensis develops a unique oyster-reef community with the associations and interactions of animal and plant populations.

The awareness regarding this edible oyster as a rich seafood resource has resulted in the growing demand for its meat in some parts of our country. This has now led to an established culture industry in India and hopes to bring foreign exchange by exporting cultured meat of this oyster.