Julie Gibbs, age 11, of Tacoma, Wash., for her question:
ARE THERE REALLY BLIND FISHES?
The average fish lives a frantic life, hunted by larger fishes and chasing smaller fishes for the food he needs to stay alive. He needs to move fast, to keep his wits about him, and most especially he needs keen eyes to spot trouble from any direction. Surely no fish could survive without eyesight. Nevertheless there really are blind and partially blind fishes‑and they survive very nicely.
The various blind fishes live in secret hideaways, where noon is as dark as midnight. Most live in gloomy, dark, underground caves, hidden from the light of day. Others live down in the deep ocean, where the sunbeams never reach. Even if these fishes had eyes, there is no light to see by.
Most of them are just a few inches long, and there is evidence that their ancestors had normal fishy eyes. Some have useless, withered eyes buried under the skin. Perhaps their ancestors were swept into secret caves by streams that dived underground. There they stayed and so did their children. After long ages, they gradually changed to suit their gloomy surroundings.
When an animal gives up using a certain part of his body, it tends to wither away. Often other advantages develop to make up for the loss. When the blind fishes lost their eyesight, most of them developed extra taste buds and sense organs to detect the finest changes in the pressure and motions of the water. Some have barbels, or feelers, that can taste the flavor of food from a distance.
Fishes that dwell in the daylight tend to wear colors that blend in with their backgrounds. The blind fishes have lost their skin coloring. Some of them are pasty white, others are tinged with pink by small blood vessels just under the skin surface.
Food in the secret caves comes in small helpings and sometimes is scarce. When bats live in the cave roofs, they drop scraps into the water. In summer, insects arrive. Some fly in, perhaps to find shelter; some are swept underground by streams. The blind fishes can sense them when they touch the water‑‑and rush in to feed.
These cave dwellers belong to various groups of related fishes on the outside. Some lay eggs, and the mother may carry them in her gills for perhaps two months. Others let their eggs sink to the bottom, and some species bear live baby blind fishes.
Life in the dark caves is quiet and a lot safer than life in the sunny streams. There are companions, but no large enemies. The blind fishes share their caves with pale blind crustaceans, pale blind salamanders and sometimes with pale blind insects.