There are 81 known species of subterranean fishes in the world. Some travel back and forth between the darkness underground and the light above, but many spend their entire lives in the pitch-blackness of subterranean rivers, streams, lakes, and springs. These are the troglomorphic species, and they have adapted to this harsh environment by the loss of their eyes and the development of numerous large sensory papillae on various parts of their bodies. These sensory papillae are sensitive to vibrations and touch and compensate for their lack of sight, permitting them to carry on life functions, such as finding food and avoiding predators, in total darkness. They also lack pigment in the skin and look pinkish because of blood vessels showing through their translucent skin.
There are two groups of troglomorphic fishes in the United States, the cavefishes of the family Amblyopsidae and the blindcats of the family Ictaluridae. The cavefishes are less than five inches in length and are found in the eastern United States. They have a large branchial cavity, which allows them to carry and incubate their eggs in the gill chamber. Because the cave systems they live in are energy poor, cavefishes eat infrequently and conserve energy by having slow metabolisms and remaining motionless most of the time. They are slow-growing and long-lived. Cavefishes feed on copepods, isopods, amphipods, crayfish, small salamanders, and even their own young.
The Alabama Cavefish is found only in Key Cave in Lauderdale County, Alabama. Its total known population is numbered at less than 100, making it one of the most endangered fishes in the world. In contrast, the Southern Cavefish is uncommonly found in caves over a fairly large area involving seven states. The two remaining troglomorphic species in this family are the Ozark Cavefish of the Springfield Plateau and the Northern Cavefish of south-central Indiana and central Kentucky. Both are considered rare, with the Ozark Cavefish being classified as a threatened species.
The blindcats consist of four species, of which two occur in the United States. These are known from five artesian wells penetrating the San Antonio Pool of the Edward’s Aquifer in and near San Antonio, Texas. They have been found to occur together in three of these wells. Both species are abundant in their habitat and occur in these subterranean waters at depths of 900–2,000 feet. The Toothless Blindcat, at four inches, feeds on fungal growths and detritus, while the Widemouth Blindcat, at five inches, is an opportunistic predator, feeding on shrimp, amphipods, and isopods.
Just as these subterranean fishes have lost their eyesight from living in total darkness, so the Christian is in danger of losing his spiritual eyesight by living in the darkness of sin. “In following the path of Satan’s choosing, we are encompassed by the shadows of evil, and every step leads into deeper darkness and increases the blindness of the heart. The same law obtains in the spiritual as in the natural world. He who abides in darkness will at last lose the power of vision. He is shut in by a deeper than midnight blackness; and to him the brightest noontide can bring no light. He ‘walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes.’ 1 John 2:11.
“Through persistently cherishing evil, willfully disregarding the pleadings of divine love, the sinner loses the love for good, the desire for God, the very capacity to receive the light of heaven. The invitation of mercy is still full of love, the light is shining as brightly as when it first dawned upon his soul; but the voice falls on deaf ears, the light on blinded eyes.” Thoughts From the Mount of Blessing, 92.