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http://news.bbc.co.uk/1/hi/7525552.stm

Live fish caught at record depth
By Anna-Marie Lever
Science and Nature reporter, BBC News

Deep-sea fish caught at record depth

A live deep-sea fish has been caught at a record depth of 2,300m on the hot vents of the Mid-Atlantic Ridge.

Three shrimp species were also pulled to the surface, researchers report in the journal Deep-Sea Research.

Scientists have engineered a new device that allows recovery of live animals under their natural pressure at greater depths than previously achieved.

Next they hope to be able to transfer the animals into an experimental lab to study their normal biology.

"Pressurised recovery has been around for the past 30 years, but this is the deepest fish-capture under pressure - the previous record was 1,400m. This is also the first time pressurised capture has occurred at a hydrothermal vent," said Dr Bruce Shillito, marine biologist at the Universite Pierre et Marie Curie, Paris, France.

The shrimp species were caught at 1,700m (5,600ft; Mirocaris fortunata and Chorocaris chacei) and 2,300m (7,500ft; Rimicaris exoculata) at two vent fields, Lucky Strike and Rainbow, on the Mid-Atlantic Ridge.
Scientists watch the deep-sea fish inside the Periscop onboard ship

Dr Shillito explains: "At depths of over 1,000m, it is difficult to recover animals alive. Catching with no pressure is as good as catching dead. Fish are the most fragile - even a fisherman with a 100m line will probably reel in a catch whose gas bladder is in its mouth."

Although the fish caught by the team was a zoarcid (Pachycara saldanhai) and had no gas bladder, it was sensitive to full decompression.

At the surface, under pressure, the fish was active and remained upright, however upon release of pressure its movement became uncoordinated and within a few minutes it was totally motionless.

A similar effect, caused by decompression, was also observed in the shrimp species. At the surface, under pressure, most shrimps were in an upright position and swimming actively and continuously.

When a separate shrimp sample was caught and pulled to the surface without pressure, the animals jerked violently, and after a few hours were dead.

The samples were examined onboard the ship "Pourquoi Pas?" during the Momareto cruise, which was organised by Ifremer, the French Research Institute for Exploitation of the Sea.
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