A still video image shows a newborn coelacanth. (Aquamarine Fukushima)

Japanese researchers have filmed a young coelacanth — a rare fish known as a "living fossil" — deep in the ocean off Indonesia.

The newborn fish was found at a depth of 161 metres off Sulawesi Island in Manado Bay on Oct. 6.

Indonesian fishermen first caught a coelacanth in the bay in 1997.

The video released by marine researchers at Aquamarine Fukushima, an aquarium near Tokyo, shows a blue fish with white spots, 31.5 centimetres long, swimming among the rocks.

The coelacanth was known only from fossils before 1938, when the first living member of the species was found in the Indian Ocean off southeastern Africa.

DNA analysis of African and Indonesian coelacanths revealed that they are separate species.

The fish hasn't changed much in 400 million years. Before living coelacanths were found, they were thought to have gone extinct about 80 million years ago.