Ecological studies on the seasonal production of the edible oyster, Crassostrea madrasensis (Preston) in Cochin backwater, Kerala

K.S. Purushan, U.K. Gopalan, T.S.S. Rao


Seasonal variation in the standing crop of intertidal oyster Crassostrea madrasensis at Ramanthuruth and Vallarpadom in the Cochin backwater for the period July 1974 to December 1975 showed that the maximum yield (whole weight) was about 20 kg/m2 in July during 1974 and 10-18 kg/m2 in March-April during 1975 at both stations. The average biomass at Ramanthuruth was significantly higher than that at Vallarpadom. In general, oysters in closeby deeper waters were significantly larger in size than the intertidal ones, but as regards percentage meat weight the latter out-weighed the former. Among environmental variables, salinity seemed to be the foremost factor in influencing the production of oysters. A large majority (90-98%) of the intertidal oysters perished during the monsoon and early postmonsoon while the subtidal population was seen to be relatively more stable. The increased rates of siltation, turbidity and pollution arising out of man made changes in the backwater seem to exert a negative influence on the existence of edible oysters and at the same time pose a threat to their consumers


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