That monster of a catch is an arapaima (Arapaima gigas - or, "this fish is BIG"). It is also called a pirarucu or paiche in the Amazon region. One can only assume that there is still another word for "freakin' huge fish."
Keen observers will notice that this fish resembles an arowana in some ways. Yes, they are related. The arapaima, however, is limited to the Amazon River basin and not found in Asia or Africa like other arowanas. The arowana types are so widespread because they first evolved on Gondwana- y'know, before the continents split up.
Which arapaima is the largest ever is up for debate; supposedly, there was an arapaima specimen over 14 feet long. The recorded average is a little over 2 meters (6.6 ft), although specimens up to 8.5 feet have been well-documented. A single one of these fish can produce over 70 kilograms of meat; as you can probably imagine, this has led to the giant fish going commercially extinct...except in Thailand, where they just LOVE breeding giant fish for fun. (No, it is not native there.)
|Tongue, scale...and trading card?|
The arapaima is not just big, it is weird as well. All osteoglossiformes (including this thing and arowanas) sport bony tongues. These are rough enough to scrape bark, and, presumably, the flesh of smaller river-dwelling munchies. Arapaimas also breathe air (as do bettas - a tidbit I was unaware of when I did that betta entry) via a labyrinth organ.
Arapaimas are well-known in popular culture. If you play any video game that involves fishing, you will probably see this big fellow as a rare catch. Hell, even Street Fighter has a reference to this giant fish. (That's Animal Crossing up there.)