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Snailfish living in deep-sea trenches in the Pacific and Indian oceans may have wider geographic distributions than previously thought, according to a researcher at The University of Western Australia.

Dr. Paige Maroni, from UWA's School of Biological Sciences, was lead author of the study in Ecology and Evolution.

The hadal zone—depths of 6,000 to 8,000 meters—represents one of the last great frontiers in marine science.

It accounts for 45% of the total ocean depth range, and although in the past 10 years research in this zone has increased as a result of technological advances, much is still unknown.

In 2023, at a depth of more than 8 kilometers underwater, a new record for the deepest fish ever filmed and the deepest fish ever caught was set by scientists from UWA and Japan.

"Ecological understanding of snailfish dwelling at depths greater than 6,000 meters still remains limited due to challenges in specimen collection and preservation," Dr. Maroni said.

Researchers examined 20 new specimens of hadal snailfish from the Japan and Tonga trenches in the Pacific Ocean and the Diamantina Fracture Zone in the Indian Ocean.

An evolutionary hypothesis and analysis to determine whether the snailfish were the same species was tested on five taxonomic groups: Pseudoliparis swirei, Pseudoliparis belyaevi, Notoliparis kermadecensis, Notoliparis stewartia and Paraliparis selti.

The evolutionary history of hadal snailfishes was informed by analyzing three mitochondrial DNA markers to assess the species' relationships and distribution patterns.

The results support the hypothesis that the genus Notoliparis should be considered a subjective junior synonym of Pseudoliparis, which if endorsed by the scientific community, could lead to widespread taxonomic changes.

The findings emphasize the challenges and limitations of using DNA barcoding solely to distinguish closely related or recently diverged species.

"The results advance the biogeographic understanding of hadal snailfish and highlight the importance of expanding sampling efforts," Dr. Maroni said.