Ribbon eel

The Ribbon Eel is a sea fish that first appeared in. In it appears only in the sea surrounding Tortimer Island, while in  it appears anywhere in the sea. It has a thin shadow size and can be sold for 600 Bells.

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

The exhibit has this to say about the Ribbon Eel:

In
The ribbon eel can be found in the coral reef tank.

During a Fishing Tourney, when given a Ribbon Eel, Chip will say the following:

Real-world 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.