Deep sea snailfish shed light on ocean life, revealing the specifics of the chemical compound that allows sea creatures to live beneath crushing pressures. Researchers from the U.S., Britain, and New Zealand have described an experiment they carried out in this week’s Proceedings of the National Academy of Sciences. In late 2011 a trap was lowered into the Kermadec Trench loaded with mackerel intended to attract the small bottom dwelling creatures hadal snailfish feed upon. Despite concern that the trap would come back up empty, the team was able to retrieve a handful of snailfish. These transparent boneless fish are little more than guts in a condom, but after the results of the experiment carried out this week they have opened the door to a deeper understanding of the limits of life on the ocean floor.
Hadal snailfish have been seen living as deep as 25,000 feet but have not been captured in over 60 years. The new batch was examined for levels of the chemical trimethylamine oxide which protects proteins from damage caused by living under the enormous pressure 25,000 feet of water imparts. This chemical is also responsible for the distinctive fish smell, so as a rule of thumb the deeper under water a fish lives, the more like a fish it will smell. Examining the deep-sea snailfish led to the conclusion that fish bodies have a limit to the amount of trimethylamine oxide they can contain, leading the team to hypothesise that fish depending on the chemical to survive would not be able to live beneath a depth of 5.1 miles. This would leave the bottom 25 percent of the ocean completely devoid of fish life.
The deep-sea snailfish shed light on ocean life in other ways as well. Their soft, translucent bodies speak of a world with no light, negating the need to develop bright colors or patterns. The high concentration of trimethylamine oxide found in the snailfish makes them important for reasons beyond oceanography; there are ongoing studies that suggest the chemical molecule that allows the fish to live at such extreme depths can be used to treat glaucoma in humans.
Despite the trepidation experienced by the scientists who captured the hadal snailfish, it is only the second deepest catch on record. The snailfish for this experiment were caught at a depth of roughly 25,000 feet, but in 1970 a cusk eel was hauled up in a fishing net lowered to 27,500 feet below the ocean waves. There is some debate however over whether the eel was living at that depth or was snagged in the net as it was brought back to the surface. Despite the second place standing, the deep-sea snailfish shed light on ocean life that reveals key features of the creatures living in the briny deep. Studying their simple body structures will likely yield new insight into how these creatures came to be so well suited to the famously inhospitable ocean depths, and provide a focused area for future oceanographers to search for new discoveries.
By Daniel O’Brien