Biology: Arapaima

One of the world's largest freshwater fish, these giants can reach 9 feet (2.75 meters) long and weigh up to 440 pounds (200 kilograms). They have a wide, scaly, gray body and a tapered head.

It seems normal but the arapaima can only stay under water for about 10 - 20 minute before it has to come up for air. Arapaimas are air-breathing, so they stay close to the surface which makes them vulnerable to human predators, who can easily target them with harpoons.

While this giant fish's habitat is relatively unmolested, overfishing has become a serious problem, and some South American authorities have attempted to enact protections.

Sources:
National Geographic
Image: petfishtalk.com