Piranha

The Piranha (ピラニア, Pirania) is a rare fish that appears in the river during the day time in the summer. It is quite expensive for such a small fish, in fact, it sells for 2,500 Bells in City Folk, making it the most expensive 'small' fish.

Donating to the Museum
In the museum, the piranha appears in the bottom right tank, middle tank (Wild World), or the right tank (City Folk), where it will bash against the walls of the tank in an attempt to reach the player.

In Animal Crossing
As a piranha is donated, Blathers will say this:

"Dear me! My mind boggles! I had no inkling that we had such frightfully dangerous fish in these waters! I suppose that would indicate they're not as lethal as they are made out to be... Or are they trying to lull us? Have no fear! We'll look after your sharp-toothed friend. For everyone's sake!"

In Wild World
Blathers will say this while a piranha is being donated:

"Piranha are rather bony. I can't say I've heard good things about their flavor. Some restaurants do serve them, of course, but as a tourist attraction, eh wot? These things probably sit about discussing OUR flavor, you know."

In City Folk
When a piranha is donated, Blathers will say this:

"Most people see piranhas as savage fish that enjoy tearing prey apart with their teeth... However, they're actually quite timid, wot wot? They're often treated like bad guys due to their scary faces. I hope we haven't hurt their feelings..."

In New Leaf
An information board in the aquarium will display this description of the piranha upon donation:

"They're known for their protruding eyes, as the name indicates, but this feature is actually a detriment. Their vision is quite poor, to the point that they will swim past food and frequently bump into things. They are a type of goldfish and get their distinguishing eye pop about two months after birth."

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 piranha has been caught, the following information can be found in the fish menu:

Giving to Wendell
When this fish is given to Wendell in, the player is rewarded with a Cracked Ground design.

Further information
The red-bellied piranha is one of the most ferocious fish. It can be found in the Amazon River. They grow to about 33 cm and weigh 3 1/2 kilograms.