The giant oarfish can grow up to five metres in length and is usually to be found at depths of 1,000 metres and very rarely above 200 metres from the surface. Long and slender with a dorsal fin the length of its body, the oarfish resembles a snake.
In recent weeks, 10 specimens have been found either washed ashore or in fishing nets off Ishikawa Prefecture, half-a-dozen have been caught in nets off Toyama Prefecture and others have been reported in Kyoto, Shimane and Nagasaki prefectures, all on the northern coast.
According to traditional Japanese lore, the fish rise to the surface and beach themselves to warn of an impending earthquake - and there are scientific theories that bottom-dwelling fish may very well be susceptible to movements in seismic fault lines and act in uncharacteristic ways in advance of an earthquake - but experts here are placing more faith in their constant high-tech monitoring of the tectonic plates beneath the surface.
"In ancient times Japanese people believed that fish warned of coming earthquakes, particularly catfish," Hiroshi Tajihi, deputy director of the Kobe Earthquake Centre, told the Daily Telegraph.
"But these are just old superstitions and there is no scientific relationship between these sightings and an earthquake," he said.