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San Diego scientists identify new fish species 6,000 feet under the sea

A pair of San Diego researchers have helped identify a new species of fish in the deep ocean waters of the eastern Pacific Ocean near Costa Rica.

The Scripps Institution of Oceanography (SIO) scientists named the new species Pyrolycus jaco.

Schmidt Ocean Institute researchers have visited, on a number of occasions, a hydrothermal site known as the Jaco Scar. It is a spot under about 6,000 feet of water, where methane seeps out of the ocean floor.


“Methane is coming up from the sea floor, but at a slightly higher temperature than the rest of the ocean,” said Charlotte Seid, the collection manager for benthic invertebrates at SIO. “Which apparently is enough to attract animals that normally only like it hot at hydrothermal vents.”

The research team operating the submersible was collecting mussels when a six-inch long eel-like fish darted in front of the submarine’s camera. The site has been visited several times since the fish was first discovered in 2009.

The fish were first seen, by SIO scientist Lisa Levin and researchers from the University of Costa Rica when they discovered the methane seep, but the fish wasn’t classified scientifically.

Four eelpout specimens were collected in 2018, and a year later the remotely operated vehicle SuBastian captured stunning high definition video footage of the pink fish.

The newly discovered fish were swimming among a tangled nest of tube worms, about the size of a minivan, that were anchored to the sea floor. The fish use the tangle of tubeworms for shelter and likely as a place to find food.


“They’re getting energy from the chemicals and the microbes that live inside their tubes,” Seid said. “And it’s a great place to be a tubeworm.”

The eelpout gets its name from related species that look like eels and have downturned mouths resembling frowns.

“You can see they don’t move very fast,” Seid said as she watched the underwater footage. “And they don’t go too far from their homes. Oh. It’s gone right back into shelter.”

Seid was working on a detailed inventory of the species when she reached out to colleague Ben Frable, to help identify it.

Frable manages the world’s largest marine vertebrate collection which is located on the Scripps campus.

“This section is kind of the group of fish, eelpouts and their relatives,” Frable said, explaining his process as he looked for similar species to confirm the fish’s identity.

The shelves, floor to ceiling, are full of underwater creatures perfectly preserved in sealed jars, but he could not find a match. He also came up short while searching for matches in genetic records. That means an exhaustive search through published literature.

“I’ve taken a look. Going through the books. Going through references. Trying to match them up,” Frable said. “They’re not really resonating with anything I’m seeing.”

So, Frable reached out to a colleague in Denmark. Peter Rask Møller is a curator at the Danish Natural History Museum and he’s considered an authority on deep sea bottom living fishes.

“(Rask Møller) immediately recognized it as this genus that has only been described in the last 20 years. It’s called Pyrolycus. Pyro - “fire” lycus - “wolf,” Frable said.

Rask Møller knew immediately the fish was something new.

That helps explain the fins, the lack of scales and the number and location of sensory pores on the eelpout’s bodies. Those pores are key to helping the fish find food.

“These animals are living in environments that are pitch black too, they’re kind of relying on not just their eyes but other organs for sensing movement and prey on food around them,” Frable said.

There are only four samples available to researchers, two in San Diego and two in Denmark.

Another researcher from Cal Poly Humboldt, Allison Bronson, used a CT scan to uncover the animal’s skeleton without damaging the specimen, providing further evidence this is a new species.

Seid, Frable, Rask Møller and Bronson co-authored the paper identifying the fish in the current edition of the journal Zootaxa.