Scripps Oceanography researchers discover new species of deep-sea fish

The purple fish at left is a new species of eelpout discovered off Costa Rica by researchers at Scripps Oceanography.
The purple fish at left is a new species of eelpout discovered off Costa Rica by researchers at UC San Diego’s Scripps Institution of Oceanography in La Jolla.
(ROV SuBastian / Schmidt Ocean Institute)

Pyrolycus jaco, a type of eelpout, is found at a hydrothermal site off Costa Rica.


A team of researchers led by UC San Diego’s Scripps Institution of Oceanography in La Jolla has discovered a new species of fish. And while excited about the discovery, it’s the where, not the what, that piqued researchers’ curiosity.

The newly identified species, Pyrolycus jaco, is the first fish species to be described from the hydrothermal seep site known as Jaco Scar, located at a Pacific tectonic plate margin off Costa Rica. The small eel-like fish, measuring roughly 6 inches long with a light pink to lavender-colored body, has been observed nestling among tube worms at depths of 5,700 to 5,900 feet.

Though there are hundreds of species of these fish — known as eelpouts for their body shape and “pouty” facial structure — the new species joins only four others known to exist on hydrothermal vents in the Pacific Ocean. Researchers describe Pyrolycus jaco in a paper published Jan. 19 in the journal Zootaxa.

Study co-author Charlotte Seid said she was part of a research group that was studying methane seeps and hydrothermal vents in the deep ocean when the discovery was made.

At methane seeps, natural gas and other chemicals exit the seafloor at the same cold temperature as the surrounding water.

At hydrothermal vents, the chemical-rich water expels dramatically like a geyser, reaching temperatures above 750 degrees Fahrenheit.

“This region of Costa Rica is our neighbor, tectonically speaking, so … by studying our neighbors and their biodiversity, it gives us a sense of the big picture of the whole eastern Pacific Ocean,” Seid said.

In finding the methane seep near Costa Rica, scientists discovered it was some 35 degrees hotter than the surrounding areas, “which made it just warm enough to be a home to creatures that normally like hydrothermal vents, which are much hotter, and attract creatures that were unlike others in Costa Rica,” such as tube worms, mussels and more, she said.

Using submersible vehicles, the team studied the biodiversity and all the species found in that ecosystem, called a hydrothermal seep.

When Pyrolycus jaco was discovered, Seid asked a colleague to identify it, not knowing it would be completely new to science. She went to Ben Frable, manager of the Scripps Oceanography fish collection, who would become the paper’s lead author.

UC San Diego researchers Ben Frable and Charlotte Seid
UC San Diego researchers Ben Frable and Charlotte Seid are co-authors of a study on a new species of deep-sea fish found off Costa Rica.
(Screenshot by Ashley Mackin-Solomon)

“This group of fish is not well-represented genetically … so our collaborators at Scripps and other parts of the world ran the genetics and couldn’t match it up to anything,” Frable said. “In trying to figure out what species it is … we looked at morphological features such as how many fin rays [spines] it has, how long its head is, what its teeth look like, those types of questions. So I did that, but I wasn’t getting anywhere.”

Frustrated by being unable to identify the species, he recruited partners around the world, including the foremost authority on this type of fish in Denmark, Peter Rask Moller.

“I sent him some pictures and X-rays and he deduced quickly that this was a genus that had been described in 2002,” Frable said. “But the other two species that these are known to be related to are from the western Pacific Ocean … and both occur on thermal vents. So it was clear this was not the same species.”

As the prospect that Pyrolycus jaco was indeed a new species started to solidify, “it was pretty exciting,” Frable said. “In the fish realm, new species are discovered on a fairly regular basis, with around 300 to 500 new fish species described every year. But this was very exciting because it was very distinct … and these fish are notoriously difficult to tell apart, hence why there isn’t a lot of genetic information.”

The new species is distinguished from similar species by differences such as shorter head length and variations in the numbers of bones and sensory pores on its body.

Eelpouts are members of the ray-finned fish family Zoarcidae, of which there are roughly 300 known species around the world, including some found off the California coast.

With the addition of Pyrolycus jaco, there are 13 known species of eelpout found worldwide on hydrothermal vents or methane seeps.

Seid said she wasn’t surprised that the team had discovered a new species, given that more of the deep sea is being explored as underwater vehicles and equipment improve. However, the discovery helps contribute to the big picture of ocean conservation.

“[These discoveries] help make any sort of data-driven, effective management decisions,” she said. “If we want to design sanctuaries or plan for the future of our ocean, we need to know the most basic data about every place we have been: what is there, how many, what species exist?

“As far as we know, this fish is not found anywhere else on Earth, so that is a great argument for protecting the habitat. But what if we find one in Chile or Mexico? We’re making those connections, which allows us to design effective species conservation plans. … But we need that baseline data.” ◆