Probe Links Fish Deaths To Trichodesmium Bloom
Investigators detected a dense bloom of Trichodesmium, a cyanobacterium known to trigger hypoxia and fish kills, in the nearshore waters. Laboratory analysis showed concentrations of up to 380 cells per millilitre.
Visakhapatnam: A preliminary investigation into the mass fish mortality at the Boyapadu Fish Landing Centre in Nakkapalli of Anakapalli district, has identified a combination of oxygen depletion and a Trichodesmium algal bloom as the likely cause.
According to a report by the Visakhapatnam Regional Centre of the Central Marine Fisheries Research Institute (CMFRI), nearly 94 per cent of the dead fish belonged to the Leiognathus genus (pony fish), a species highly sensitive to low dissolved oxygen. Fish carcasses were found strewn along a 1.5-km stretch of the shoreline, with the estimated biomass loss exceeding 11 metric tonnes.
Investigators detected a dense bloom of Trichodesmium, a cyanobacterium known to trigger hypoxia and fish kills, in the nearshore waters. Laboratory analysis showed concentrations of up to 380 cells per millilitre. The fish were found with open mouths, a typical sign of respiratory distress, while examinations revealed no evidence of disease or lesions.
Dissolved oxygen levels ranged between 3.28 and 4.38 mg/L, below the level required to sustain healthy marine life. Nutrient concentrations were also found to be favourable for algal growth. The report said intermittent rainfall and sudden temperature changes may have triggered the bloom, while its subsequent decay likely worsened oxygen depletion, creating lethal conditions for bottom-dwelling and nearshore fish.
Local fishermen, however, alleged that industrial effluents, particularly from nearby bulk drug manufacturing units, could have contributed to the incident. They claimed offshore wastewater pipelines might have intersected fish schools and driven them into polluted waters.
The CMFRI team said the available evidence did not conclusively establish industrial discharges as the cause. However, it noted that the possibility could not be ruled out without long-term monitoring. The report recommended detailed studies on water quality, toxicology and phytoplankton to determine the exact cause of the fish mortality.