An international team of researchers used state-of-the-art underwater cameras to find the new fish at the bottom of the Atacama Trench in the eastern Pacific Ocean at a depth of 7,500 metres (24,600 feet) -- and were surprised at their abundance in such an inhospitable environment.
"These things are right on the limit of what all fish can take so you might expect at that depth you'd maybe be lucky to see one or two eking out an existence," Alan Jamieson, senior lecturer in marine ecology at Newcastle University told AFP on Friday.
"But there's a whole heap of them sitting there."
Temporarily named the pink, blue and purple Atacama snailfish, the previously unknown creatures are 20-25 centimetres (8-10 inches) long, translucent and have no scales.
They appear to be uniquely adapted to conditions four-and-a-half miles beneath the ocean surface, where the days are permanently pitch black and water temperatures barely top two degrees Celsius (36 Farenheit).
At such depths, the pressure is so great that larger animals would be crushed under their own mass.
"It's the equivalent of having an 800-kilogramme weight placed on your little finger," Jamieson said.
Researchers believe the fish may have evolved to live on the sea floor to avoid larger prey.
"The hardest structures in their bodies are the bones in their inner ear, which give them balance, and their teeth," said Thomas Linley, a Newcastle research associate who went on the expedition.
In fact, being made almost entirely of a gel-like substance, the fish would die without the crushing pressure holding them together.
"Their bodies are extremely fragile and melt rapidly when brought to the surface," Linley said.