Arapaima

The Arapaima is a river fish that appears in late summer. It will only appear between the hours of 4pm and 9am. It is a very rare fish, and that is why this fish is the third most expensive river fish (10,000 bells), after the Stringfish and Dorado and tied with the Arowana (which it is related to). Its shadow size is huge, and likewise it is the largest river fish. In the 'Bugs and Fish' window in Animal Crossing: City Folk, it is the last river fish. The fish is the second largest fish in the game, after the shark at about 550 centimeters and it is tied for length with the ocean sunfish.

In Wild World
Blathers' speech is as follows, when the arapaima is donated to the Museum:

"You might think a fish this big might not be appetizing, but it's simply delicious! The arapaima used to be abundant, but overfishing has sadly made them rare. One has to wonder how many species must suffer to satiate the world..."

When donated, it'll be in the second tank in the first room.

In City Folk
"My, it is massive, isn't it? Not just large, but the largest river-dwelling fish in the world, it's said. Records indicate a specimen some 200 inches in length has been sighted before... Looking at it now, the theory that this fish hasn't changed in 100 million years seems believable!"

This fish, when donated, will appear in the middle right tank.

Encyclopedia Information
Once the player has caught a particular fish or bug, they can find information about it in the bug or fish menus. Once the arapaima has been caught, the following information can be found in the fish menu:

Further Information
The arapaima is the largest freshwater fish in the world and it can be found in the Amazon River which is in the continent of South America. It is sometimes called the pirarucu or paiche. This fish can grow to about 3.2 metres, but normally about 2 to 2.5. The supposed maximum length is 4.5 metres, although this comes from an early 19th century second-hand report, and it has not been confirmed.The arapaima male is supposed to be a mouthbrooder, meaning the young are protected in its mouth until they are older. The female arapaima helps to protect the male and the young by circling them and fending off potential predators. Arapaimas breathe air and get their red coloring from their diet of red crusteceans.