From the collected informations and data above information and the data, it appears that the cause offish mortality observed between 13th and 15th May, 1987 at the Palk Bay side of Mandapam was mainly due to the natural phenomenon resulted by the ecological changes restricted to an area of about 3-4 km* between the shore and the coral reef. It was possible that the phytoplankton blooms reported just before the phenomenon and its isolated occurrence immediately after the incidence, and the associated changes in the water quality, the mixing up of the polluted water drained from the Mandapam fish landing centre and its subsequent spread within the reef area due to the prevailing water current would have triggered off an anoxic condition in the water column causing stress in the environment and consequent mortality of the fishes. Further, the absence of any physical and biological symptoms as revealed by the examination of the dead fishes, their gills and the gut contents, and the absence of any report of untoward incidents on the consumption of the dead fishes excluded the possibility of the cause of the reported mortality due to poisoning, pollution or the use of explosives
