Scientists catch a live fish at a record depth in the Mid-Atlantic Ridge

July 31st, 2008 - 1:58 pm ICT by ANI  

London, July 31 (ANI): Scientists have caught a live deep-sea fish at a record depth of 2,300m on the hot vents of the Mid-Atlantic Ridge.

According to a report by BBC News, this was possible because of a new device that allows recovery of live animals under their natural pressure at deeper depths than previously achieved.

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.

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, explained Dr Shillito.

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 three shrimp species that were captured by the team. 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 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.

The new sampling system for pressured recovery, which has been named Periscop, was developed by Dr Shillito in conjunction with Gerard Hamel, a mechanics engineer at the Universite Pierre et Marie Curie.

It has three compartments which perform different tasks - capture at depth, recovery of the deep-sea species under natural pressure, and transfer to the lab with no decompression.

The plastic capture box is attached to a submersible arm which allows movement and suction for sampling. The animal is then transferred into a pressurised box. This is kept at the same pressure as the sampling depth during ascent by a pressure compensator.

We used pressurised water to maintain pressure, which is a safer and a simpler alternative to gas. We hope this method of pressurised recovery will become standard, said Dr Shillito. (ANI)

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