The creature, which held up against the fisherman's arm looks to be at least two feet long, completely stumped its hunters when they pulled it out of the water. They believed that it may be a mutated version of a Chinese sleeper (Perccottus glenii) - also known as the Amur sleeper - which is a freshwater fish native to the Amur River basin in eastern Asia. According to local reports, locals kept the species as domestic animals when they were first introduced to Russia back in the 1940s. Several owners were said to have released them into rivers and local sewage systems when they got too big for their water tanks.