Ōnamazu

The Ōnamazu is a legendary catfish said to live beneath the earth's surface. Imprisoned by the thunder kami Toyofutsu-no-kami, the ginormous catfish is believed to be the cause of earthquakes when it thrashes about, attempting to break free. It is said that Toyofutsu pins the Ōnamazu down with a large stone to keep it from moving. Sightings of large, restless groups of catfish in rivers and lakes are said to be a herald of an earthquake.