Mass mortality of fish and shellfish species was recorded from Ormara (East Bay) in October 2016. Initially a few dead fishes were observed to be floating in the open sea in the East Bay area. With the passage of time, mass mortality was observed on the south-western part of the East Bay and heaps of fish were found floating in the area. This event of mass mortality was only confined to the Oramara (East Bay) and not spread to other parts of Oramara coast. In order to determine the dynamic of the fish mortality and its spread in the area, sampling of the water of the area was collected on regular intervals. It was observed that Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921 was present in extremely large numbers (highest recorded concentration 13 cells/ml) which led to depletion of oxygen in the area resulting in mortality of large number of fishes. In this fish kill demersal (bottom dwelling) as well as pelagic species (surface dwelling) were found dead in the area in large numbers. Groupers (Epinephelus spp.), Chinese pomfrets (Pampus chinensis), mullets, shrimp (Penaeus spp.) and crabs (Portunus spp.) were dominated in the dead fishes and shellfishes. Oxygen depletion was observed to confine to south-western part of the Ormara Bay where highest number of dead fishes were observed. The phenomenon of mortality of fishes continued for 8 days whereas normal condition started prevailing in 15 days and no mortality was observed after 20 days since the start of the mortality phenomenon.
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