Though stingrays do not readily attack humans, they are one of the few 'monster fish' that can pose a real danger to those who handle them. Large stingrays have been known to pull boats upstream and even underwater, Hogan said. Stingray numbers appear to have dropped dramatically in recent years as their riverine habitats have degraded. Stingrays locate prey, usually clams and crabs, with a sensor that can detect an animal's electrical field. They often bury themselves in sandy or silted river bottoms and breathe through holes, or spiracles, located on top of their bodies. Giant stingrays occur in river systems in Thailand, Borneo, New Guinea and northern Australia, Hogan said. They are brown to gray in color, wide and flat in form, and they sport a long, whip-like tail.

These ancient fish, little changed over many millions of years, can reach 16.5 feet (5 meters) long and weigh up to 1,320 pounds (600 kilograms). No one is sure how many giant stingrays are left, which habitats they prefer, or even if they ever venture into the ocean, where their more commonly known relatives dwell.

The giant freshwater stingray ( Himantura polylepis) is one of the largest freshwater fish in the world, Hogan said.

Biggest fish on planet