The arapaima is the largest fresh water fish in the world, reaching up to 9 feet and weighing up to 440 pounds. This fish is mainly found in rain forest rivers in South America. While it does stay under water for 20 minutes at a time, the arapaima can often be seen swimming along the surface. This also makes it a prime target for hunters with harpoons.Bonus Fact: The arapaima has a “bony” tongue.