From Nookipedia, the Animal Crossing wiki
The Frog (カエル, Kaeru) is the most common of the pond fish, although as a frog, it is not a fish, but an amphibian. It sells for a low amount of 120 Bells. It has a distinctive croak heard when the player is approaching it. It appears from May to August all day long.
Donating to the Museum
In Animal Crossing
"Greeeeeee! Gree! Gree! That's my best Sonoran green toad impression, wot! We do keep frogs and toads here. Well, then, let's get our amphibious friend settled. All the damp comforts of a home. Guaranteed."
The Frog sits on a lilypad on the top right tank in the aquarium upon donation.
In Wild World
"'This forgotten pond,
"That was a haiku, eh wot? Rather an incomprehensable one, but one nonetheless. Many find frogs repulsive, but they're so prevalent, even poets sing of them!"
The Frog sits on a lilypad on the back tank of the first room in the aquarium upon donation.
In City Folk
"Fascinating... Were you aware that frogs make slight adjustments to their croaks to communicate? Hoo, they say many things to each other! For example, "ouch," "flee," "I like you ♥," and so forth. With enough practice, maybe I can learn to speak with our amphibian friends! ...Hoo-ribbit! Hoo-ribbit!"
The Frog appears in the middle-left tank on a lilypad floating on the surface. It makes no movements, other than croak and move with the lilypad.
In New Leaf
"These former tadpoles prefer to live near ponds and other damp and swampy places. They dwell on land, so they have lungs and skin as opposed to a set of gills. They like to stick close to water because they require a nice, moist lifestyle. Frogs are moist because they emit a liquid to protect their skin from dryness. If too much moisture evaporates from their thin skins, they could have trouble breathing. It's better not to handle frogs, as some species are poisonous, even to the touch!"
The Japanese tree frog is very common and is of least concern on the IUCN Red List.
Names in other languages