Extreme cave fish with ‘alien’ appetites

TEXAS A&M (US) — Could life exist on planets less hospitable than our own? Scientists studying a tiny Mexican fish say it’s quite possible.

“The fish we study are extremophiles, meaning they are adapted to life at the edge of biological tolerance,” says Katherine Roach, a graduate student at Texas A&M University in the wildlife and fisheries sciences department.

Roach, together with Kirk Winemiller and collaborator Michael Tobler, recently authored a paper on the fish published  in the journal Ecology. The small fish they studied is Poecilia mexicana found in the Cueva del Azufre or the “cave of sulfur” located in Tabasco state, Mexico.


The small (about 2.5 inches at maturity), almost blind fish live in total darkness swimming in oxygen-starved water with hydrogen sulfide concentrations so toxic they would kill most other life forms, according to Roach.

“Our research shows that organic carbon produced by sulfur bacteria oxidizing dissolved hydrogen sulfide, a process called chemoautotrophy, is the main food source for the fish,” Roach says. “Though it is known that simpler life forms flourish by feeding through this process, ours is the first study to actually document a fish, a true vertebrate, directly receiving its sustenance through bacteria performing chemoautotrophy.

“Their ecosystem in the cave is basically self-sustaining without much input from plants at the surface. As a result, our research has implications for discovering life outside the earth. If these complex vertebrates can thrive on sulfur bacteria, why couldn’t similar, more evolutionary derived organisms be supported by chemoautotrophic bacteria on other moons or planets such as Europa, one of Jupiter’s moons? It may not be altogether impossible.”

Roach explains that most of the earth’s ecosystems have food chains supported by organic carbon produced from the fixation of atmospheric carbon dioxide by plants using sunlight. These, in turn, release breathable oxygen into the atmosphere.

Roach says another study in Movile Cave in Romania a few years ago examined a population of macroinvertebrates that have been isolated in the cave for some 5.5 million years, which also feed on chemoautotrophic bacteria. She says that study generated enough public interest to warrant its own Wikipedia page and notes that author E.O. Wilson highlights this case study in his book The Future of Life.

“What makes our study so exciting is that we’re the first to actually document a fish, a relatively large and complex vertebrate, that is able to thrive by being solely supported by chemoautotrophic-processed hydrogen sulfide bacteria,” Roach says.

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