From Nookipedia, the Animal Crossing wiki
The Guppy (グッピー, Guppī) is a rare fish found in the river during the months of April through November between 9am to 4pm. It is rarer during the month of April, but will become easier to find as the months go on. It sells for 1,300 Bells in Tom Nook's Store. Its shadow size is tiny.
Donating to the Museum
In Animal Crossing
"Hoo hoo! Hullo, little fishy! Aren't we a tiny little fellow! Adorable! Why, I believe it stuck it's tongue out at me! Hoo-rumph! Nevertheless, we'll take care of the little blighter! I'll keep an eye on this mischief-maker myself!"
In Wild World
"Many don't know that the guppies with ornate tails are actually the males! Indeed, the females are quite dull...much like Celeste, always stargazing. I really wish she would pay attention to something else on occasion... Ah! I'm terribly sorry! That wasn't what we were talking about, was it?"
In City Folk
"Male guppies are known for their colorful, bright scale patterns... But look closer, and you'll see males share a design with their female peers... Indeed, a matching couple! It seems like the pairs are a little shy about their romance and tend to hide it. Simply adorable!
The Guppy can be found in the small tank in the bottom-left of the aquarium, with other tiny fish in City Folk.
In New Leaf
"Guppies are tropical fish that are related to killifish and live in warm rivers. They are popular fish that have been bred to have beautiful flowing tail fins. Mother guppies give birth to their babies after the eggs hatch in their bellies. They give birth at a rate that's nearly constant, so their population tends to grow rather quickly."
Once the players have caught a particular fish or bug, they can find information about it in the bug or fish menus. Once the Guppy has been caught, the following information can be found in the fish menu:
The guppy is one of the most popular freshwater aquarium fish species in the world. It is native to Barbados, Brazil, Guyana, Netherlands Antilles, Trinidad and Tobago, the US Virgin Islands and Venezuela.
Names in other languages