Blue snailfish found in the deepest ocean depths.

A photograph of a blue snailfish taken in the deep sea off the coast of South America.  Professor Alan Jamieson and Dr. Thom Linley
A photograph of a blue snailfish taken in the deep sea off the coast of South America.

Professor Alan Jamieson and Dr. Thom Linley

Snailfish can be found in every ocean on the planet, at depths ranging from shallow intertidal to the deepest oceanic trenches. Twenty of the 400 identified species are found in the eastern Pacific, off the west coast of South America. Although shallow-living species are well studied, those that live in the deepest oceanic habitat, known as the hadal zone, are poorly understood.

In 2018, an international team of scientists investigated the fauna of the Atacama Trench, a vast underwater subduction zone that runs along South America's west coast and is as deep as the parallel-running Andes Mountains. The deepest parts of this trench, between 6,000 and 8,000 meters below sea level, are in the hadal zone, which is characterized by immense pressures, freezing cold temperatures, and total darkness. It is not surprising that the fauna inhabiting this trench has received little attention.

The team of researchers, which included scientists from Newcastle University, used specially designed underwater cameras and lights that were lowered to these depths on custom-built, free-falling landers. The bait in the form of mackerel was attached to the landers to attract organisms to the area, and traps allowed some of these to be collected. The two landers were lowered to the depths on 18 separate occasions and recorded the presence of numerous small, deep-sea creatures, including three different types of snailfish.

Previous studies of deep-sea trenches in a variety of locations confirmed the importance of snailfish in the hadal zone. They are suction-feeding predators that feed on the numerous small amphipods (crustaceans) that live in the depths. However, due to a scarcity of samples, the true diversity and distribution of snailfish species remains unknown, particularly in the deepest regions of the ocean. The researchers identified one type of snailfish from the camera footage that was unfamiliar to them and appeared different from what they expected.

The small blue fish, seen between 6,000 and 7,600 meters deep, did not resemble other hadal snailfish. Instead of being pale with small eyes, it was blue with large eyes, which was unusual for a creature that lives in complete darkness. With these characteristics, it resembled other species of snailfish found in much shallower waters.

The team was able to capture one of these unknown individuals and bring it to the surface. Although it died as a result of the extreme pressure change, the researchers were able to compare the new species to other members of the snailfish family using microcomputed tomography (micro-CT) and DNA analysis. The new species is named Paraliparis selti in their description, which was published in the journal Marine Biodiversity, with the specific name meaning 'blue' in the Kunza language of the indigenous peoples of the Atacama Desert.

Surprisingly, the new species appears to be a distinct colonizer of the Atacama Trench, establishing a new lineage of deep sea snailfish. It is not related to the other species found in the area. Species in the genus Paraliparis are particularly abundant in the Antarctic Southern Ocean and are rarely found at depths greater than 2,000 meters. This is the first time a species from this genus has been discovered living in the hadal zone.

Dr. Thom Linley, a visiting researcher at Newcastle University and the study's lead author, stated, "I find this family of fishes absolutely fascinating." They are not what we expect from a deep-sea fish, and I enjoy demonstrating to people that the world's deepest fishes are actually quite cute."

"It's made of inches thick stainless steel and sapphire glass for me to get a camera down to where these animals live." It then films these delicate and beautiful animals that have adapted perfectly to this harsh environment. We can only visit these animals for a short time with our engineering-built force."

"We've been wondering for a long time what it is about this type of fish that allows it to live so deep. Perhaps it was a series of lucky accidents, a random fluke that occurred in one lineage. The discovery of this new species indicates that it is larger than that. "Lightning struck twice, and this Family is something special."

"Paraliparis selti offers a fantastic opportunity to investigate what enables fish to live so deep." If we only studied one lineage, we'd never know which traits are just part of that lineage and which are the deep-sea secret sauce."

The researchers conclude that the new species may have evolved from cold-adapted species of the Southern Ocean, and its discovery and genetic data will aid in understanding how this remarkable group of fish evolved, adapted, and diversified into the deep sea. This tiny blue fish raises new questions about the relationship between cold temperature and high-pressure adaptation, as well as a new understanding of how and when life evolved to live in the deep.


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