In the Muttukadu Baclcwater Meretrix casta (Chemnitz) is a continuous breeder with two peak periods of spawning - March-April and in August-September. The length composition of commercially exploited dams ranged between 22 mm and 42 mm and the 28.0 - 33.9 mm group was [wedominant. Large scale mortality of clams in the fish culture pond and backwater was observed in May 1985 and March 1987 respectively. An attempt was made to correlate spawning and mortality of clams in the backwater with salinity, temperature and dissolved oxygen