Loach

The Loach is a fish found in the river at all times of the day during the months of March through to May, making it the only fish restricted to the Season of Spring. It is much harder to find during May.

Donating to the Museum
The loach can be donated to the Museum by talking to Blathers. During the donation, Blathers will say the following about the loach:

In City Folk
"The loach is a slippery, somewhat vile-looking fish...but in truth, it can be quite useful, wot? For ages, some cultures used the loach as a poison treatment. It also tastes great in a hot pot... A bit of wisdom for the day, eh wot? One must never judge a person, or a fish, by its appearance..."

The loach can be found in the middle-left tank.

Further Information
It is unclear what type of loach appears in Animal Crossing, due to the vast varieties of loaches that exist, but it is most likely the Chinese Weatherfish, also known as Dojo Loach (it may also be one of the Acantopsis genus). The fish in City Folk appear to be a different species.

The Chinese Weatherfish, as a member of the Cobitidae family of loaches (True Loaches) which live in fast flowing waters, it is a bottom feeder. All Cobitids are "bottom feeders," meaning they swim at the bottom of rivers and tanks eating the algae at the bottom. They also eat small crustaceans and insects, but only during the day.

The below information comes from another website. Source: http://animal-world.com/encyclo/fresh/loaches/DojoLoach.php

This remarkable fish is quite hardy and adaptable, very easy to care for. They wiggle about in an eel like fashion scavenging the bottom for leftover bits of food, even munching on snails. They also like to dig and burrow into the substrate often burying themselves. Provide an aquarium that is large enough for its playful antics, have a soft substrate of sand or fine gravel, and have a good filter for the detritus they stir up. They are most active in the evening, so during the day they like hiding and resting places created with rocks and wood. Plants are nice but they should be potted.

The Dojo Loach or Weather Loach is available in aquariums in both its wild form and in a gold variety. In its wild form this loach has dark greenish gray to dark brown spots over a yellowish brown body (often mottled) with a paler belly. The gold variety can range from a yellow to an orange color and they are usually thin bodied. They do have spots but they are usually extremely faint.

These fish have some very unique qualities. The Dojo Loach or Weather Loach are very 'pet-like'. They can be trained to take food from your hand and even enjoy being touched. They are jumpers. Should they happen to leap out of their home, they can survive for a time even out of the water. A couple of ways they do this is by producing a thick mucus coating that keeps them moist; and by being able to swallow air, absorbing atmospheric oxygen through their hind gut.

The Weather Loach here, Misgurnus anquillicaudatusis, is one of three species commonly referred to as a weather loach. The other two are Misgurnus fossilis and Cobitis taenia. They all come from similar environments and have similar behaviors, and are best identified by their color patterns with M. anguillicaudatus being spotted and M. fossilis having horizontal stripes along the body. It is still being discussed whether the spotted one is simply a subspecies of the striped one, though they come from different geographical areas.

Trivia

 * When the player catches a loach in Animal Crossing, the player says, "You don't suppose it's Hylian, do you?" This is a reference to the Hylian Loach from the Legend of Zelda series (another game from Nintendo's arsenal), where it is considered both the rarest fish and a legendary catch, similar to the Coelacanth from the Animal Crossing games.