The fish are closely associated with colonies of gray bats, another endangered species in Missouri. It is thought guano from the bats feeds the small invertebrates that in turn provide a ready food source to the cavefish.
Food competition may also have led Ozark cavefish to evolve an interesting reproductive strategy. "All evidence so far shows us that when the females lay their eggs they actually put them in their mouths and brood them in their gills," Salveter said.
If so, that would mean females would hold fertilized eggs in their gill chamber for four to five months. While unproven, Salveter notes that the shape of the fish's mouth and the fact that biologists have never been able to locate a "ghost fish" nest in the cave, suggests this to be the case. "We think that their eggs would be gobbled up by something if they didn't basically hide them in the gill chamber," she said.
While some early settlers may have referred to the fish as a ghost fish, it was also generally called a "well watcher."
"Settlers knew intuitively that their well water was safe to drink if those fish were present," Salveter said.
The belief has some truth to it. Because underground cave systems tend to be very stable, their inhabitants are highly adapted to their environment. They do not adjust easily when faced with rapid environmental change.
That role makes it easy to see why such a tiny, reclusive animal can be important even in today's modern society. The Ozarks region is a karst region, a limestone geology of thousands of underground caves, streams and sinkholes.
In much of the area, humans literally live above cave systems that can extend up to 100 miles (160 kilometers) or more. Rain water, pollutants, and other runoff from these aboveground "recharge" areas ultimately end up in the underground water system. It's creating a direct connection to the groundwater source, which happens to be where the Ozark cavefish live.
"It's kind of the canary-in-the-coal-mine thing," said Rick Horton, a fisheries management biologist with the Missouri Department of Conservation. "If the ground water quality gets so that it won't support the cavefish, well, lots of people are dependent on that water for their drinking supply. A pollutant that's affecting the cavefish is going to be affecting you."
This crucial link makes the shaky status of the fish a cause for even greater concern. "The population decline seems to suggest that the underground water supply isn't safe to drink in some places," Amy Salveter noted.
The culprits of diminishing water quality are varied. Chemical pollution can be a problem, but so can nutrient runoff and other products of erosion driven by agricultural operations and development. Ozark cavefish country is a booming region, encompassing growth spots in Missouri, like Springfield and Branson, and Fayetteville, Arkansas.
The majority of known Ozark cavefish sites are on privately owned land, so Horton and his colleagues know that to protect the fish they must reach out to people.
They seek to educate the public about steps to limit soil erosion, maintain vegetation, and keep or establish natural buffer zones near water access points like streams, sinkholes, and cave entrances to help improve water quality. They also ask people not to block or otherwise alter cave mouths and sinkholes.
Horton describes the response as "hit and miss." "A lot of people who have these fish know that they're there, but they are a bit ambivalent," he said. "Some are very protective of them and glad that they've got them. Others, well, anytime that you talk about threatened or endangered species they become a little ill-at-ease."
For Horton, that's when the message of education is most important to the future of this unusual animal. He said when talking to the public "we stress [that] it's your property, and you can do what you want. But if you'd like to help this critter, we can show you some things that you can do that will help."