Sole congregate on underwater volcanoes

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Scientists have observed an unusual flatfish congregating around underwater volcanoes in the waters of the Pacific.

Huge numbers of sole were filmed around hydrothermal vents in the Mariana Arc, a 1200km/745 mile chain of volcanic seamounts and islands in the Pacific Ocean between Japan and Guam.

The sole live in waters where hydrothermal vents pump out heated seawater, laden with metals and chemicals, which are populated by a range of extremophile organisms.

The fish are believed to be a new species from the Symphurus genus.

Dr John Dower, a fisheries oceanographer at the University of Victoria, Canada, told the BBC:

"There are a lot of toxic heavy metals coming out of these active volcanoes. The water is very warm, and it can be very acidic, the pH can be as low as two like sulphuric.

"And yet here we've got a group that has not previously been seen in this type of environment and they're doing very well - they're actually thriving.

ExtremophilesA number of invertebrate species, including shrimp, crabs, worms and bivalves have been recorded from the Mariana Arc, but very few fish have been found there, says the report.

Dower told the BBC that the sole are found at very high densities, 100 times greater than typically seen on the continental shelf.

The massive density of flatfish is believed to be being supported by the presence of worms and possibly bacteria that live upon the sediments.

The fish, which reach up to 11cm/5" in length, seem capable of withstanding extremely high temperatures and have been recorded near sulphur pools measured at temperatures of over 180C/355F.

"We have video of a fish sitting on the molten sulphur and then moving off after a couple of minutes, apparently unharmed", Dower told the BBC.

"They seem to be able to tolerate an environment that no other flatfish, and very few fish in general, are found in."