Recent weeks have seen the mysterious deaths of more than 70 giant freshwater stingrays in Thailand's Mae Klong River.
Officials are not yet certain what killed the enormous fish. Among the possibilities raised thus far include excessive water acidity or poisoning from a recent ethanol plant spill, National Geographic reported.
The species (Himantura polylepis) is among the largest fish living in fresh water and can exceed 6 feet wide and 8 feet long and can weigh more than 1,000 pounds.
Found in larger rivers in Southeast Asia and Borneo, they eat small fish as well as various crustaceans and molluscs. They're sometimes caught accidentally in fishing lines and are under threat because of issues such as habitat loss due to dam construction and pollution from manufacturing and new construction occurring alongside their rivers.
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The cartilaginous fish are considered endangered, according to the International Union for Conservation of Nature (IUCN) "red list" of threatened species.
"Pollution impacts the species in the Thai parts of its range especially...in the Bang Pakong River, 30 specimens were found dead in one day in 2008-9 as a result of a pollution incident," the organization notes.
Local wildlife officials have established a "war room" to study whether or not toxic wastewater killed the fish, and Thailand's prime minister has ordered an investigation into the deaths, asiaone reported.
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