Loss of Pigment Many cave dwellers have long been known to show this. If a creature living in the normal, outside world were to have a mutation causing a loss of its pigment, it would normally be less able to survive, losing some protection against sunlight. However, in a cave without the sun, such a mutation can readily spread through the population. Loss Of Eyes Blind fish, with scars where eyes normally appear, have long been known to exist in certain caves. A mutant gene damaging the genetic information for eye manufacture would have no selection pressure opposing its spread in a lightless environment.
Eyes are complex structures, prone to disease and injury.
If a fish with eyes bumped into a cave wall in the dark, it could damage the eye surface, introducing infection leading to death. The acidic environment would also be detrimental to eye health. After many hundreds of generations, the eyeless gene would confer a slight but significant selective advantage. In the thousands of years since the Flood, the Romanian cave-dwelling creatures have had time to go through a huge number of their short generational life cycles, allowing them plenty of time for maximum adaptation to their new environment. These are clearly adaptive to their dark environment.