Video – Deepest ever Living Fish

Marine scientists filming in one of the world's deepest ocean trenches have found groups of highly sociable fish swarming nearly five miles (7700 metres) beneath the surface. When the international team recovered their high definition cameras from record-breaking depths in the Pacific Ocean, they were astounded by the abundance of life. The team was investigating the Hadal zone - an area of the Ocean that sits 6,000m -11,000m below sea level. The deep sea is split up into the Bathyal, Abyss and Hadal zones, and Hadal is the deepest of the three.

There are very few places in the world deep enough to fit into this category, and most lie in very narrow trenches around the Pacific rim. The fish, who normally live in utter darkness, are completely blind, and use vibration receptors on their snouts to navigate and find food. The researchers expected fish at this depth to be relatively sedate to conserve energy, but found them to be surprisingly active.

Professor Priede, director of Oceanlab, said: "There is the question of how do animals live at all at these kinds of depths.

"There are three problems: the first is food supply, which is very remote and has to come from 8km (5 miles) above.

"There is very high pressure - they have to have all sorts of physiological modifications, mainly at the molecular level.

"And the third problem is that these deep trenches are in effect small islands in the wide abyss and there is a question of whether these trenches are big enough to support thriving endemic populations."

But this species appears to have overcome these issues, added Professor Priede.