The study showed that Arapaima populations were now extinct in eight of the 41 communities studied, and extremely low on average. The researchers trained fishermen to count the fish as part of a large-scale survey.
The researchers said that the effects of overfishing on Arapaima, which is a tropical fish, was worse than previously thought.
Study results are reported in Aquatic Conservation: Freshwater and Marine Ecosystems. Arapaima can weigh more than 28st 8lb (181kg) and are among the largest freshwater fish in the world.
These fish are air-breathing and come to the surface every five to 15 minutes, which is why they are caught easily. The fishermen use harpoons and gillnets to catch this large-sized fish.
The study done by scientists, led by Dr Leandro Castello, from Virginia Tech, US, was focused on knowing how healthy the arapaima populations in the Lower Amazon region were.
Castello and his team also wanted to find out whether these fisheries supported bio economic predictions or the alternative fishing-down theory which predicts that large and easy-to-catch fish will soon get extinct due to overfishing.
A total of 182 fishermen, who were considered to be "experts" on fisheries by their colleagues were interviewed by researchers. The fishermen were from 81 communities covering 401.5 square miles (1040 kilometres squared) of Amazonia floodplains.
The researchers also carried out the counting of fish in 41 of those communities where they interviewed the fishermen.
The survey showed that arapaima populations were depleted in 76% of the survey area, locally extinct in 19%, over-exploited in 17%, and well-managed in just 5%.
In 2% of the communities they were un-fished. The research team said the results support "fishing-down" predictions.
Dr Castello said: "Mainstream thinking has predicted that scarcity would drive up price, which would increase fishing costs and help save depleted species. But that is not what has happened."
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