How deep can a fish go? Scientists may have answer

They may look like guts stuffed in cellophane, but five fish hauled up from near-record depths off the coast of New Zealand are providing scientists with new insights into how deep fish can survive.
In a paper published this week in the Proceedings of the National Academy of Sciences, scientists from the US, Britain and New Zealand describe catching translucent hadal snailfish at a depth of 7 km.
By measuring levels of a compound in the fish that helps offset the effects of pressure, the scientists say they've concluded that fish likely can't survive below about 8,200 metres. That would mean no fish at all live in the deepest one-quarter of the world's oceans.

The snailfish have little pigmentation due to the lack of light in their environment, hence their translucent appearance.
New Zealand marine ecologist Ashley Rowden, a co-author of the paper, said nobody had caught a snailfish in nearly 60 years and so he wasn't overly hopeful when they sent down a box-like trap into the Kermadec Trench near New Zealand in late 2011.
He said they used mackerel as bait to attract the small sandhopper-like creatures the snailfish feed upon.

"When it came up, it was just amazing to see. It was 'Oh my God, we've got the fish, and we've got more than one,'" Rowden said.

Rowden said he put on gloves and carefully picked up one of the fish.
"It was like a water-filled condom," he said.
The fish are the second-deepest recorded catch. In 1970, a boat off the coast of Chile reported catching a cusk eel at a depth of 8,370 meters in a trawl net, although questions remain whether that fish was caught at the ocean floor or higher up as the net was hauled in.