PORTO VELHO - Brazil's Chico Mendes Institute for Biodiversity Conservation (ICMBio) is investigating the cause of a fish kill involving hundreds of fish in the Lago do Cuniã Extractive Reserve, in the municipality of Porto Velho, Rondônia state, in the Brazilian Amazon. The incident drew public attention after residents shared videos showing dead fish floating on the lake's surface.

Most of the fish found belong to the species locally known as branquinha, a member of the Curimatidae family. According to ICMBio, it is the most abundant fish species in Lago do Cuniã and is also the most sensitive to sudden temperature changes and declining dissolved oxygen levels in the water.

To determine the cause of the die-off, researchers from the Biogeochemistry Laboratory at the Federal University of Rondônia (UNIR) will analyze the lake's water quality. The leading hypothesis is that a sharp drop in dissolved oxygen levels, triggered by changes in the lake's physical and chemical conditions, caused the mortality.

Researchers believe the most likely explanation is that the accumulation of organic matter, combined with high temperatures and rainwater carrying debris into the lake, accelerated the decomposition process. As oxygen levels declined, the fish may have suffered hypoxia or anoxia—conditions caused by oxygen deprivation—which impair respiration and can ultimately lead to death.

The Lago do Cuniã Extractive Reserve is home to about 115 families who rely on fishing and other subsistence activities. According to ICMBio, the investigation also aims to inform local residents about the causes of the fish kill and the potential impacts of the event.

Amazon Agency