These fish are both long and heavy. They can reach up to 10ft in length, with some sources claiming a maximum length of 15ft (4.7m). They weigh up to 220kg (485lbs). They have copper-green heads and black bodies, with lighter scales in the center.
The fish’s large, bony scales protect them from piranhas and other natural predators of the rainforest. The scales can be up to 6cm long each. They have long, narrow bodies and tail fins that are round and small, which work well for them in the slow-moving rivers that they call home.
Their dorsal fins stretch along their backs. Their bony tongues are the defining characteristic of the bonytongue fish or Osteoglossiformes.