An exceptionally rare deep-water shark called megamouth swims in a water tank on a fishing boat before being released into the ocean. (Video footage provided by Toba Aquarium and Chokyu Suisan)

MINAMI-ISE, Mie Prefecture--For the second time in a week, Japanese fishermen have snagged an ultra-rare megamouth shark in local waters.

The deep-water fish measuring 5.1 meters was released into the ocean as it was deemed to be healthy.

In the previous instance off Tateyama in Chiba Prefecture early May 22, the megamouth survived for only one day.

The shark netted in the Kumano Sea off Mie Prefecture on May 26 was placed in a water tank on a fishing boat and brought to a fishing port in Minami-Ise here.

Staff from the Toba Aquarium confirmed it was a female megamouth and took a blood sample. As the shark was deemed relatively healthy, it was returned to the ocean.

The shark was netted about 20 kilometers south of Owase Port in Owase, also in Mie Prefecture, before dawn on May 26. It was trapped in a roll net about 100 meters below the surface.

The megamouth caught earlier in the week was also female. It was transferred to an underwater cage and initially seemed to be healthy. But it died the next day.

The species was discovered off Hawaii in 1976. Since then, there have been about 110 sightings worldwide, about 20 of which were in Japanese waters.