Pirogusu

Pirogusu are eel-like creatures that squirm from openings in the walls of the Swamp Palace in A Link to the Past. At first only their eyes can be seen, then they worm forward before they drop down into the shallow water below. Once in the water, Pirogusu move very fast, skimming through at high speed and travelling in straight lines around the edges of the water, similar to Rats, except they will not stop until they are defeated. Pirogusu will also continue to swarm into the room even after being defeated, often appear alongside Hover and Kyameron, making the water a constant threat. Pirogusu can cause a surprising amount of damage despite their small size, up to two hearts, so should be treated with caution.

Trivia

 * Pirogusu appear to have barbels, much like catfish and carp. These can only be seen before it enters the water.
 * The second half of its name in Japanese, is very similar to the name of the Rat enemy in Japan,, which may suggest a relation.