Hypoxia from Algal Bloom Suspected in Mass Fish Death on Andhra Coast, CMFRI Reports

A preliminary investigation by the ICAR-Central Marine Fisheries Research Institute (CMFRI) suggests that hypoxia, or oxygen depletion, likely caused the mass mortality of fish along the Boyapadu coastline in Anakapalli district, Andhra Pradesh. The event, reported on June 20, 2026, resulted in an estimated loss of over 11 tonnes of fish, valued at approximately ₹4.96 lakh.

The CMFRI team visited the site on June 21 and observed a massive aggregation of dead fish stretching 1,500 metres along the shoreline. Nearly 94% of the dead were pony fishes (Leiognathus), a species common in shallow coastal waters. Laboratory examinations found no external lesions or signs of disease, but most fish exhibited an 'open-mouth' condition—a symptom often associated with respiratory stress and oxygen deficiency.

Environmental studies revealed an extensive bloom of Trichodesmium, a type of cyanobacteria, in near-shore waters at a concentration of 380 cells per millilitre. Such blooms are known to cause hypoxic conditions when the biomass decays, leading to oxygen depletion. The team noted that intermittent rains may have created stratified water layers, and a sudden temperature rise likely triggered the bloom, followed by oxygen depletion at the bottom. When oxygen-depleted water was flushed ashore during high tide, it may have trapped and killed the fish.

Local fishermen attributed the mortality to industrial effluents from nearby bulk drug industries, pointing to discharge pipelines extending about 2 km offshore. However, the CMFRI report states that observations and laboratory findings are insufficient to definitively establish industrial pollution as the cause. Structured interviews with 10 fishermen confirmed that schools of fish were washed ashore alive before dying on the beach.

Notably, researchers observed a complete absence of seabirds and scavenging birds along the affected stretch, despite the abundant biomass, suggesting possible contamination or unusual conditions that deterred scavengers.

The CMFRI has recommended comprehensive water quality, toxicological, and phytoplankton investigations to determine the exact mechanism behind the mortality. The report was submitted to the Andhra Pradesh Pollution Control Board (APPCB), which had initiated the inquiry.