Ribbon eel

The ribbon eel (ハナヒゲウツボ, Hanahigeutsubo) is a fish that can be found exclusively in the ocean surrounding Tortimer Island in. Having a thin shadow size, the ribbon eel is able to be caught any time in any month. It can be sold for 600 Bells.

Donating in New Leaf
After donating a ribbon eel to Blathers, it will appear in the section for fish and deep sea creatures, specifically in the top-right most tank in the north-western room.

The exhibit has this to say about the Ribbon eel:

''"Ribbon eels have long, ribbonlike bodies and look as if they have flowers sprouting from their noses. They get their name from their bright, vivid color, in addition to the length of their skinny bodies. Ribbon eels hatch sexless before first becoming males, then females as they age. Their tendency to stick their heads out from holes in the sand and open their mouths is not a sign of anger. In actuality, they're merely taking a breath. Oddly, they're surprisingly peaceful creatures, despite the look."

Further information
The ribbon eel, also known as a Bernis eel, has a life-span of up to twenty years, although they almost always die within a month of captivity. Ribbon eels often are within rocks or other enclosing structures and breathe with their mouths open, often giving off an angry or aggressive appearance.