Crucian carp

The crucian carp (フナ, Funa), tied with the frog and the bluegill as the second-lowest selling fish in the game, can be found in the river. It sells for 120 Bells. Along with the Carp, and most fish of the Carp family, it appears in the first tank in and the middle-left tank in. The Crucian Carp is a greyish white color. These fish are extremely common, found at any time of year and any time of day.

In City Folk
When donating the fish to Blathers in the Museum, he will say:

"The largest difference between a Crucian Carp and a Carp is the former's lack of whiskers, wot? Compared to the regally whiskered Carp, there's something almost common about the Crucian variety!"

In New Leaf
Upon donation to the museum, the information board in front of the tank that houses the crucian carp says:

"Crucian carp are fairly easy fish for beginners to catch, but they're also popular with veteran anglers. They are related to koi and can live up to 15 years, making them a great fish to keep in a pond. Male offspring are seldom born, so females significantly outnumber males, making populations suffer. Luckily, females can reproduce with males of some other species, so the problem is relatively temporary."

Further Information
The Carassius carassius is a fish of the Carp family. People commonly have these in aquariums, but there are also people that eat them. They are related to the Goldfish.