By Charlie Denison
A rare creature lives deep inside the caves of Kentucky. Translated from Latin, its name means “Cave-dweller with injured eyes” (Amblyopsis spelaea). But the eyes of this creature are not injured; instead, they’ve ceased to be. Where this animal lives there is no light, so functioning eyes would be merely a waste of energy. Because of this, the northern blind cavefish is a unique species that lives a unique life.
The fish is found only in the deep waters of Midwestern caverns. The farthest north they’re found is in Bedford, Ind., and the farthest south in Mammoth Cave. Mammoth is the longest cave in the world at 365 miles, and inside the cave is the Underground River, where the blind creatures can be found.
University of Louisville professor William D. Pearson used to work as an aquatic biologist for Mammoth Cave. In that time, he tagged a few blind cavefish to monitor and study.
“These fish have no pigment in their skin. You can see right into them. When we found them, we could see the [tag] number through their skin,” Pearson said.
The fish hardly ever swim in groups. “The blind cavefish have their own territorial areas. Rarely will you see many of them together,” said Jim Richards, general manager of Bluesprings Caverns in Bedford, Ind.
Pearson agreed with Richards: “The most I’ve ever seen in one cave is about 400.”
Living in darkness, the cavefish still manage to live up to 50 or 60 years.
“It’d be hard to make a living in the cave, but some animals have it much worse,” Pearson said. “There are no predators chasing the cavefish and they always have food available.”
“Mammoth Cave also has blind crayfish and blind shrimp, which the fish often eat,” explained Vickie Carson, spokeswoman for Mammoth Cave.
Carson said the first written accounts of the blind cavefish were from visitors. “Stephen Bishop, a slave, guide and explorer, was the first to really take notice of the fish. This was around 1842.” However, Richards pointed out that they’ve existed for much longer.
“We’ve been told that these fish have existed since before the last Ice Age,” Richards said.
Pearson cracked a smile when asked about the crayfish that the cavefish consume. “I once found a cavefish with two antennae sticking out of its mouth. It looked like it had swallowed a crayfish whole. I still wonder how long it took to digest that thing.”
Richards said the fish don’t get very large on that diet. Their average size is two to five inches. “The biggest ones we’ve seen here were six to seven inches,” she said. “They’re fortunate there’s nothing larger in the waters because they’re nothing intimidating.”
How have the fish lasted so long without eyes? “Every third year the fish lay about 60 eggs which they store in their gills until the right time comes,” Pearson explained. “There are currently less than 10,000 northern cavefish left in the world, which makes them pretty rare. However, they are not considered endangered.”
Another reason the blind cavefish have been around so long is their established breeding season which includes the late summer and early fall seasons.
“Since they are not able to use day length as a calendar like surface-dwelling fishes do, they probably rely on some other seasonal cues in the cave environment, such as slight temperature changes in the water, water levels, and seasonal inputs of organic matter,” Pearson said. Since resources are scarce in cave streams, the average female cavefish may take one to three years to mount up enough energy for a set of 80 eggs.
“I have found two females carrying clutches of eggs in the gill chambers and several others carrying broods of about 60 larval fish as long as 12 millimeters in their gill chambers,” said Pearson. “When these females were netted and placed in a bucket they spit out the young fish — presumably under stress of the capture. We placed the mother and these mothers and her young back in the stream, but I could not see if she gathered up her young or not.”
An adjusted breeding pattern is not the cavefish’s only unique instinct.
“These fish have an unusually advanced sense of vibration,” Richards said. “This helps them find their food and stay away from any trouble that may occur in the water.”
Pearson has also studied some cavefish in laboratories outside of the cave. “With no pigment, the fish are surprisingly unaffected by light. However, they are very sensitive to temperature change,” he said. Anything under 45 degrees or above 60 degrees made the fish uneasy.
Pearson also mentioned that, being as these fish are the top predators in their systems, cannibalism may have occurred in the past and may be occurring now.
Researchers continue to study this fascinating fish. Jessie Ballowe, a former student of Pearson’s, is currently studying the northern blind cavefish’s eating habits at the Louisville Zoo.
Pearson is currently teaching Introduction to Ecology. If blind cavefish and other unusual organisms interest you, consider taking a look at his courses for the fall.
Mammoth Cave tours cost anywhere from $4-$45. Visit their website at http://www.nps.gov/maca/index.htm for tour and ticket information.
John Lennon once sang, “Living is easy with eyes closed.” Perhaps, for the northern blind cavefish, this quote rings true.
