Fish in one of the ocean's deepest trenches have taught researchers how low they can really go.
Scientists captured five hadal snail fish using special equipment at a staggering depth of 7000 meters (about 22965 feet), a NIWA news release reported.
The last time humans caught a member of this species was 60 years ago; they are the second deepest fish ever spotted alive, the news release reported.
The recent voyage aimed to gain insight into the "biochemistry of fish living in deep water." The team was especially interested in their trimethylamine oxide (TMAO), which is a stabilizer that counteracts the effects of pressure from the deep water. The deeper the species tends to live the higher their levels of TMAO are.
The researchers wanted to find out if there was a "physiological limit to the colonisation of the deepest ocean depths," the news release reported.
TMAO levels in shallower fish suggested these creatures were limited to depths of about 8,400 meters, but researchers had never looked at the TMAO levels of fish that lived deeper than 5,000 feet below.
The Kermadec snail fish's TMAO levels showed the fish could most likely reach depths of 8, 200 meters; this suggests fish cannot live in the bottom 25 percent of oceans.
The snail fish were caught using baited traps; the bait attracted small organisms which in turn attracted the deep-dwelling fish. The first expedition was unsuccessful, but the samples were gathered during a second voyage.
"It's pretty tricky at that depth. A lot of effort went into it - we knew that if we caught them as deep as possible it would go a long way to testing the hypothesis," Marine ecologist Doctor Ashley Rowden said in the news release.
"Catching five of them also meant we had the physical specimens to confirm their taxonomic characteristics," she said.
