THERMAL TOLERANCE STUDIES IN WEDGE CLAM DONAX CUNETAUS (BIVALVIA - DONACIDAE) IN RELATION TO THERMAL DISCHARGE FROM MADRAS ATOMIC POWER STATION, KALPAKKAM (EAST COAST OF INDIA)Syed Mohamed. H. E., Krishnamoorhy R., Venugopalan V.P., Sadiq Bukhari A. and Shahul Hameed P
In Atomic and thermal power plants the temperature difference (DT) between intake and outfall assumes greater importance for laying down legal limits for thermal discharges. In order to ascertain the adverse impact of elevated temperature on the life of aquatic animal such as wedge clam Donax cuneatus (L.), experiments were conducted at different (DT) temperature and their thermal tolerance was assessed from percentage of mortality. The thermal tolerance experiments were conducted in the field as well as in the laboratory. In the field, the cage experiments were carried out in the thermal discharge canal located on the coastal site where Madras Atomic Power Station (MAPS) discharge the thermal effluent. In the laboratory, the experiments were conducted in two modes: 1) Gradually increasing temperature and 2) Direct exposure. In the Upper Incipient Lethal Temperature experiment 100% mortality of Donax cuneatus was found in 75 minutes at 48oC and in the lower Incipient Lethal Temperature experiment no mortality was found at 20oC for 48 hours. Percentage of mortality due to direct exposure in different DT (DT 5oC (33oC), DT 7oC (35oC), DT 10oC (38oC) and DT 12oC (40oC)) at 48 hours was observed that there was no mortality at DT 5oC and DT 7oC. However, 50 % mortality was recorded at DT 10oC and 70% in DT 12oC. Field experiment on thermal tolerance of Donax cuneatus at the discharge canal indicated that elevated temperature (above 35oC) of the heated effluent could not affect the organisms.
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