The fishery and biological aspects of Meretrix casta of Pulicat Lake have been studied. The clam production of the lake was estimated to be 309.7 and 168.2 tonnes in 1980 and 1981 respectively. During 1980, the clam fishery was supported by clams ranging between 34 and 49 mm and the dominant size groups were 37-39.9 and 4042.9 mm. The percentage edibility was found to be high twice in a year during February-March and July -August. Females were dominant sex and indeterminate were found to be high during the periods of March-May and October. Sexually mature clams were found almost throughout the year in the lake and three peaks of spawning activity were noticed in March-April, July-August and October-November. The larvae of the trematode parasite Bucephalopsis haemeanas was noticed in the species during the period September-November and It caused considerable damage to the gonad.