Skullfish

Skullfish are skeletal fish enemies which prowl the waters of Majora's Mask and Twilight Princess.

Majora's Mask
Skullfish live in the seas around Great Bay, as well as in the water just outside Goron Village after defeating Goht in Majora's Mask. They spawn at certain intervals within the bay and swim towards Link, biting him if he does not raise his defenses. Zora Link's electrical attack makes quick work of these pests.

Twilight Princess
In Twilight Princess, Skullfish appear in the Lakebed Temple, as well as several secret caves around Hyrule Field. They can be caught with the Fishing Rod, and will even drop a Recovery Heart when released, although they are illegal fish and will not be recorded in the fish journal.

Trivia

 * The Japanese name of the Skullfish is "Sukarugyo", which is derived from the English word "skull" and a Japanese word for fish,.
 * Skullfish are similar to Bago-Bago, an enemy in The Adventure of Link.
 * Skullfish are similar to an enemy in the Mario series game Super Mario World called Fishbone.