Hypoxia likely killed thousands of fish on Anakapalli coast, CMFRI study says

Large-scale fish mortality reported along the coast of Boyapadu, primarily affecting Leiognathus species, coincided with the presence of near-shore algal blooms and signs of oxygen stress in the affected fish.

While local fishermen suspect the influence of industrial wastewater, observations and laboratory findings are insufficient to establish a definitive cause. However, water samples showed high densities of Trichodesmium cells.

A comprehensive survey of water quality, toxicology and phytoplankton is needed to determine the exact mechanism responsible for mortality over a continuous period.

The investigation, led by the Visakhapatnam regional center of ICAR-Central Marine Fisheries Research Institute (CMFRI), focused on the Boyapadu Fish Landing Center in Nakkapalli mandal of Anakapalli district.

Following reports of mortality on 20 June 2026, experts visited the site the following day and observed a massive accumulation of dead fish along the shoreline that stretched approximately 1,500 meters in length and 5 meters in width. About 94% of the dead were identified as pony fish (Leiognathus), commonly found in shallow coastal waters

The estimated biomass of dead fish, based on the findings, is valued at around ₹4,96,889. This figure is calculated based on an approximate total weight of 11.04 tonnes of fish at a cost of 45 per kg.

Preliminary Investigation Report

“Preliminary Investigation Report on Fish Mortality Incident, Nakkapalli” submitted by Dr. Joe K. Kizhakudan, Principal Scientist and Head of ICAR-CMFRI Visakhapatnam Regional Center to Chairman Andhra Pradesh Pollution Control Board (APPCB) in Vijayawada.

The report was prepared based on an inquiry initiated by Shankar, Joint Chief Environmental Engineer (JCEE) at the APPCB Zonal Office and subsequent discussions held during a video conference between the CMFRI team and the APPCB Chairman.

Observation

Laboratory examination of the collected samples did not reveal any external lesions or signs of disease or pathogenicity. However, a notable observation was the “open mouth” condition exhibited by most fish, a physiological symptom often associated with respiratory stress and oxygen-deficient conditions. In addition, the researchers noted a complete absence of seabirds and birds of prey in the affected section, despite the abundance of biomass.

Structured interviews were conducted with 10 local fishermen who witnessed the incident on June 20 at approximately 2:30 p.m. during high tide.

Eyewitnesses reported that schools of fish were washed ashore alive before dying on the beach. Most of the local community pointed to potential contamination from the large-scale drug industry nearby. Fishermen suggested that an industrial waste water discharge pipe, which stretches about 2 km offshore, may have created zones that affected the fish before they were pushed ashore.

Algae flower

Environmental studies have pointed to extensive algal blooms in coastal waters characterized by dense coloration. The analysis revealed the dominance of Trichodesmium – a type of cyanobacteria – at a concentration of 380 nos/ml.

Experts noted that Trichodesmium blooms have been linked to “fish kill” events through mechanisms such as hypoxia. The team also analyzed temperature and nutrient levels, noting that occasional rains may have created stratified zones where a sudden rise in temperature triggered a bloom, which in turn led to oxygen depletion at the bottom as the biomass decayed.

Preliminary assessment

A preliminary assessment by the ICAR-CMFRI team suggests that the mortality was probably due to hypoxic conditions, as evidenced by the open-mouthed condition of the fish and the presence of a Trichodesmium bloom.

The report states that when anoxic water is flushed toward the shore during high tide, it traps benthic fish in a traumatized state, rendering them unable to swim. While the findings point to eutrophication and oxygen dead zones, the institute stressed that further investigation of discharge sites by local industries and ETPs is necessary to fully understand the impact.

An investigation has been launched

Reports from Anakapalli Fisheries District officials say that the fishermen have specifically alleged pollution caused by the Hetero Complex in Nakkapalli. As a result, an inquiry was ordered in which government officials and experts worked together to assess the full extent of the environmental impact on the region’s marine wealth.

Published – 28 Jun 2026 11:54 IST