for National Geographic News
"It's almost translucent. It has a whitish look, but really almost no color," said David Hendrix. "It has no eyes whatsoever. It does come across as sort of ghost-like."
The creature of which Hendrix, manager of the United States Fish and Wildlife Service Neosho National Fish Hatchery, in Neosho, Missouri, speaks is no poltergeist. Rather, it's the Ozark cavefish (Amblyopsis rosae).
Known as a "ghost fish" to some, the colorless, two-inch-long (five-centimeter-long) blind fish inhabits scattered underground sites in Missouri, Arkansas, and Oklahoma.
One place the fish is found is within a cave pool on the property of Neosho, Missouri's Neosho National Fish Hatchery.
While the bigger business of Neosho lies in rainbow trout and sturgeon, Ozark cavefish were discovered there by chance in 1989. A staffer found them while checking on water quality in one of the four cave-fed springs that supply the hatchery water.
Today the cavefish is listed as endangered by the Missouri Department of Conservation. The United States Fish and Wildlife Service (FWS) lists them as threatened.
"Someday we hope to try to propagate them," Hendrix explained. "But for now, we just protect the population hereand also seek to educate the public."
At the spring pool where the fish live, an underground camera allows the hatchery's nearly 45,000 annual visitors to observe the fish inside their native cave.
In the sparse environment of the cave ecosystem, life for its inhabitants is lived on the edge. Resources are in short supply. So creatures like the Ozark cavefish must be highly adapted to their unusual environment.
"Because they have evolved in near-total darkness, they have no eyes or need for them," Amy Salveter, a biologist with the FWS in Columbia, Missouri, said of the sightless fish. "They have sensory organs located on the tail fin, in either two or three rows, and also on the headall over them essentially. They can detect movement and chemical changes in the water and respond to those as an indicator of a food source."
Food choices are slim in the cave environment. Ninety percent of the time, the Ozark cavefish dines on copepods, a type of tiny aquatic invertebrate. But the fish is also known to eat larval salamanders, tiny crayfish, and even other juvenile Ozark cavefish.