Video shows hundreds of dead fish in Lake Cuniã; ICMBio investigates causes The Chico Mendes Institute for Biodiversity Conservation (ICMBio) investigates the causes of the deaths of hundreds of fish recorded in the Lago do Cuniã Extractive Reserve (Resex), in Porto Velho. The case gained repercussion after residents released videos showing the dead animals floating in the water (see above). According to the agency, the phenomenon is usually recorded between the months of June and July. Most of the fish found dead belong to the species known as branquinha, from the Curimatidae family. READ ALSO: Police are looking for suspect of killing ex-partner with a shot to the head while she was sleeping VIDEO shows moment of accident that killed 18-year-old motorcyclist According to ICMBio, the branquinha is one of the most abundant species in Lake Cuniã, which explains the large number of fish affected. Furthermore, it is more sensitive to sudden changes in temperature and reduced oxygen levels in the water. To identify what caused the mortality, researchers from the Biogeochemistry Laboratory at the Federal University of Rondônia (Unir) will analyze the conditions of the lake's water. The hypotheses raised by ICMBio are based on studies on floodplain lakes in the Amazon. The main suspicion is that there has been a sharp drop in the amount of oxygen dissolved in the water, caused by changes in the physical and chemical conditions of the lake. The agency explains that, although the cold can mix the layers of water and alter oxygenation, this is not considered the main factor responsible for the episode. The most likely hypothesis is that the accumulation of organic matter, combined with high temperatures and the entry of rainwater laden with debris, intensified the decomposition process in the lake. This process increases oxygen consumption, especially in deeper areas. With less oxygen available, fish can suffer hypoxia or anoxia — conditions caused by a lack of oxygen — which makes breathing difficult and can lead to death. The Lago do Cuniã Resex is home to around 115 families who depend on fishing and other subsistence activities. According to ICMBio, the investigation also seeks to guide residents about the causes of the mortality and the possible impacts of the phenomenon. Hundreds of dead fish in the Cuniã lake in Porto Velho Reproduction