Deep-sea fish are the subject of research in New Zealand. Five fish caught at near-record depths are showing how some of these aquatic animals can survive far under the ocean surface. 

Hadal snailfish have been observed living as far as 25,000 feet beneath the surface of the water. They are nearly transparent. The lack of light that deep under water gives animals little need to evolve dramatic colors or patterns. It had been 60 years since the last time a member of the species had been captured by biologists. 

Ashley Rowden, a marine ecologist from New Zealand, lowered a trap, baited with mackerel, into the Kermadec Trench in order to catch one of the elusive creatures. He was amazed when he recovered several of the animals from the ocean floor. 

"It was like a water-filled condom. A sloppy, gelatinous mass that moves between your hands. It was very cool, and very strange to see its organs and everything," Rowden told reporters. 

Researchers studied a chemical in deep-sea species that counters some of the effects of living at great depths. Trimethylamine oxide protects proteins from damage at the enormous pressures at which the animals live. Body systems of fish seem to have a limit on how much of the chemical they can store. Because of this, they believe the compound would likely be ineffective at depths over 5.1 miles. Paul Yancey of Whitman College, who was the lead author of the paper announcing the results, suggested this could reveal a maximum depth for the creatures. If these animals cannot live far underwater without this chemical, than there may be no fish at all in the bottom 25 percent of the world's oceans. 

Rowden's capture of the snailfish was, at least, the second-deepest catch ever made. A cusk eel was caught in a fishing net sent down to nearly 27,500 feet in 1970. Biologists are still undecided whether than animal lived at that depth, or was caught as the net was reeled back up to the ship. Several snailfish were recorded on video, living more than 24,600 feet under the surface of the waves. 

Trimethylamine oxide is the chemical that gives fish their distinctive smell. So, a general rule-of-thumb is the deeper in the water fish live, the more they smell. The compound may also find a use in human medicine, as a treatment for glaucoma. 

Study of the deep-sea creature was published in the Proceedings of the National Academy of Sciences.