Fish & Fisheries

Discovery: New Cave Fish Species Sees “Light of Day”

March 20, 2013

Caves remain one of the most unexplored ecosystems; scientists are still discovering new species. Ethan Inlander/TNC

By Darci Palmquist, senior science writer

Deep inside a remote cave in northern Vietnam, Craig Leisher aimed his headlamp at the water. Several small, strange-looking fish flashed by. He readied his butterfly net and quickly tried to scoop one up but missed. He tried again.

Leisher eventually caught four species of fish. Further analysis revealed that two species were already known to science, one was a new species and one was a mystery.

The new species, Schistura mobbsi, has no eyes, no pigmentation, large nostrils and limited lateral lines (how fish sense motion). It is a type of loach — a river-dwelling genus that includes both subterranean and above-ground species.

Leisher and ichthyologist Maurice Kottelat recently published the discovery in Ichthyological Explorations of Freshwaters … 10 years after the fact.

Why did it take 10 years for Schistura mobbsi to make its public appearance in the scientific literature?

Let’s re-wind.

It Started with a Sentence in a Guidebook 

The location of Phuong Hoang Cave, where Leisher and Mobbs made their discovery.
The location of Phuong Hoang Cave, where Leisher and Mobbs made their discovery.

In 2002, Leisher was living in Vietnam and looking for new places to scuba dive in his free time. Now a social scientist for the Conservancy, Leisher is a bit of a Renaissance man — a certified trimix diver and amateur birder who recently spent a year living off the grid with his family.

“An old edition of the Lonely Planet Vietnam guide mentioned a cave with a river that made for a good stopping point on the road north from Hanoi,” says Leisher.

Intrigued, Leisher’s friend and fellow diver, Jerry Mobbs, set out to find the cave one weekend.

“Going into a cave that has never been explored is probably the biggest thrill in caving,” explains Leisher. “But all we really wanted was a place to go diving.”

After the first ‘sump’ (a cave passage that’s underwater), Mobbs found he could wade up the river it was so shallow. For cave diving, it was a disappointment. But it had the potential to be ecologically fascinating, so Mobbs made a plan to come back again — this time with Leisher.

An Obscure Species in an Obscure Place 

A type of loach, Schistura mobbsi has no eyes, no pigmentation and a limited ability to sense motion.
A type of loach, Schistura mobbsi has no eyes, no pigmentation and limited lateral lines.

Caves are unique environments — always dark, with high humidity and specific mixtures of gases and nutrients. They can seem nearly devoid of life, yet every cave is a virtual petri dish of possibility for unique evolutionary adaptations. And this singularity offers fascinating material for science: Recent research on cave-fish species has yielded new insights into circadian rhythms, sleep and even evidence of the super-continent Gondwana.

On his first trip into the cave, Leisher noticed several kinds of fish in the river. (See a video of their dive.) On a subsequent trip he brought his butterfly net — and discovered just how hard it is to catch a blind fish.

“Most cave fishes I have collected are quite adept at avoiding a net,” agrees John Sparks, assistant curator in the department of ichthyology at the American Museum of Natural History in New York City. “Even though they are blind, they avoid potential predators via the laterosensory system – sensors on the snout and head.”

Leisher eventually came out of the cave with one Schistura mobbsi. The specimen was 31 mm long and very soft, making it difficult to measure and examine. With only one sighting, the researchers concluded the species could possibly be rare or else living in “specific parts of the caves which have not yet been thoroughly explored, such as narrow crevices.”

“This fish, Schistura mobbsi, is adapted to live in this cave. It’s a small niche,” explains Leisher.

A Decade Later

The science of cave biology is ripe for metaphor: dimly-lit, groping in the dark, Indiana Jones-style biology. Exploration of caves is time-consuming, and collecting adequate specimens for identification can be challenging.

“It can take a long time to do taxonomical research to determine if a species is new or not, particularly in a poorly studied area,” explains Leisher.

But 10 years between the discovery and debut of Schistura mobbsi seems rather long, doesn’t it?

It actually turns out that a decade of lag time isn’t so bad: A recent study found the average “shelf life” of any species discovery is 21 years between collection and publication. The authors of the study noted a variety of reasons for this — everything from who makes the discovery to type of species to tenure concerns of young scientists.

“There’s still one mystery fish from the cave, and in perhaps another 10 years, we’ll know where it fits taxonomically,” jokes Leisher.

In the meantime, he doubts anyone has explored the cave (named Phuong Hoang) since. He wrote his email address on waterproof paper and left notes at the beginning of the cave and at the end. So far, he hasn’t gotten any emails.

Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.

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