WELLINGTON, March 5 (Xinhua) -- A rare catch of fish from 7 kilometers below the surface of the Pacific Ocean has given New Zealand and Scottish scientists a glimpse into life in the deepest parts of the world's oceans.
Five hadal snail fish were caught using specialized equipment at a depth of 7,000 meters in the Kermadec Trench, northeast of New Zealand, and analyzed by New Zealand's National Institute of Water and Atmospheric Research (NIWA).
It was just the second time the species had been caught, the last being more than 60 years ago, and they were the second deepest fish ever seen alive.
The scientists measured their levels of trimethylamine oxide ( TMAO), a stabilizer capable of counteracting the effects of pressure at depth, NIWA marine ecologist Dr. Ashley Rowden said in a statement Wednesday.
TMAO levels were known to be higher the deeper a fish lived and the team wanted to test whether fish had a physiological limit to the colonization of the deepest ocean depths.
Measures of TMAO in shallower-dwelling fish had led scientists to predict that fish may be limited to depths of around 8,400 meters, but no measures of TMAO had been obtained from fish found deeper than 5,000 meters.
The Kermadec snail fish had the highest ever recorded TMAO content, leading the scientists to conclude that the maximum depth a bony fish could survive was 8,200 meters, and that no fish could live in the deepest 25 percent of the ocean between 8,200 and 11, 000 meters.
The expedition by NIWA and Scotland's University of Aberdeen also observed the snail fish at a depth of 7,500 meters.
In the Japan Trench, a species similar to the Kermadec snail fish had been observed at 7,800 meters.