Eyeless catfish have been discovered deep inside a cave in Texas, an entirely new area for a rare species and a finding scientists say could mean underground caverns link the US to Mexico.
The albescent pink fish were found swimming in a limestone cave at the Amistad National Recreation Area, near Del Rio in southern Texas. The tiny, 3in-long fish, identified as the Mexican blindcat, were collected by a team in May and reported this week by the University of Texas Austin.
“Since the 1960s there have been rumors of sightings of blind, white catfishes in that area, but this is the first confirmation,” ichthyologist Dean Hendrickson said in a statement. “I’ve seen more of these things than anybody, and these specimens look just like the ones from Mexico.”
Before the find, the eyeless fish were only rumored to live north of the Rio Grande: the endangered fish were only known in waters fed by the Edwards aquifer, beneath the Mexican state of Coahuila.
In April of last year, a National Park Service employee and caver named Jack Johnson saw several strange and indolent fish – their blood visible through translucent skin – swimming in the waters of an Amistad cave. Eventually, Johnson and biologist Peter Sprouse, of private surveying firm Zara Environmental, found the fish within the cave system.
Hendrickson has spent years searching for the Mexican blindcat in the US. He identified the fish for the team of researchers. Texas has two other species of blind catfish: the toothless blindcat and the widemouth blindcat, which live deep in the aquifer below San Antonio.
Subterranean natural selection strips life of the features necessary under the open sun – sight, skin, size and more. In lightless waters, creatures need no eyes, no pigment to resist the sun, no scales. The blindcats rely on sensitive hearing, touch and taste to circle in on insects and tiny brine shrimp.
The skeletal widemouths, of the genus “Satan”, are considered the top predators of the caves, even though they measure only 5.4in and have just the useless remnants of eyes – a pale sightless miniature of their closest relatives, the 5ft flathead. They are thought to prey on tiny shrimp and the 4in toothless catfish, a bizarre animal thought to scavenge on fungus and the dead.
“Cave-dwelling animals are fascinating in that they have lost many of the characteristics we are familiar with in surface animals,” Sprouse said, “such as eyes, pigmentation for camouflage and speed.”
Instead, such animals often evolve what Sprouse called “extra-sensory abilities to succeed in total darkness”.
The Mexican blindcat was first documented in 1954, after scientists discovered the miniature fish swimming in the dark wells and springs of northern Mexico. It is thought to have sensitive skin that can detect organic material that might serve as food.
The newly captured fish were taken to the San Antonio Zoo, which has a special lab designed to house cave life. The blindcats’ appearance in Texas caves supports the idea that underwater caverns beneath the Rio Grande link aquifers under Texas and Mexico.
Both the widemouth and toothless catfish live in the Edwards aquifer, whose wells – sometimes as deep as 1,000ft – provide San Antonio’s drinking water. Texas is riven with cave systems, which are homes to clouds of bats, blind salamanders, fish, pseudoscorpions and spiders.
“Aquifer systems like the one that supports this rare fish are also the lifeblood of human populations and face threats from contamination and over-pumping of groundwater,” Johnson said.
