Eel

The Eel (ウナギ, Unagi) is a special fish in the games because it is the only fish with a long and thin shadow. It is a rather expensive fish, selling for 2,000 Bells at Tom Nook's store. The fish is another summer fish, of which there are many, and appears in the evening and night.

In Wild World

 * "Grilled eel is supposedly quite succulent, but I have a bit of advice... Do NOT bring live eels to a cookout. Causes a bit of a scene, don't you know." —Blathers

The eel can be found swimming close to the bottom and occasionally hiding behind the rocks in the river aquarium in the first fish room.

In City Folk

 * "Eels are often thought of as river dwellers... but they actually go out to sea to lay their eggs, eh wot? If you can look past their slimy nature, you might notice they have round, expressive little eyes!" —Blathers

The eel can be found in the right tank in the museum as a brown colored line moving across the bottom.

In New Leaf
"Eels are born in the ocean but swim upstream through rivers when they become adults. They do, however, eventually swim back to the ocean when it is time to lay eggs. Their blood can be toxic, which is why you've never heard of eel sashimi. It's just too dangerous. Cooked eel, however, is edible and has no poisonous effects to speak of, making it a popular dish. For a long time, the egg-laying locations and habits of eels were largely a mystery. However, they are gradually being revealed through research, making eels a very hot topic of study."

Further information
The American eel, Anguilla rostrata is a fish that spawns in salt water. After hatching, the baby eels make their way to North America, on the east coast. The eels, if hungry enough, may eat their own family to survive the trip to America. They prefer to hunt at night, which is referenced by the time it appears at in Animal Crossing.

Toy set
The eel appeared in a toy set along with Purrl, a cat villager, a Koi and a fish tank.