From Nookipedia, the Animal Crossing wiki
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 Animal Crossing: Wild World and the middle-left tank in Animal Crossing: City Folk. The Crucian Carp is a greyish white color. These fish are extremely common, and can be found at any time of year and at any time of day.
Donating to the Museum
In Animal Crossing
"Even run-of-the-mill, common fish are valuable resources, you see. All part of the grand tapestry, wot! We will take excellent care of this fellow, oh yes. You can rest assured. Excellent care, indeed."
In Wild World
"When I hear Crucian Carp, I think to myself... Taco! Indeed, FISH taco, wot wot! I suppose this might be an odd choice of fish for such a dish, but... I say, by any chance, would you like to try it out and get back to me?"
In City Folk
"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."
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 Goldfish.
Names in other languages