How the cavefish lost its eyes—again and again

Cavefish have a remarkable evolutionary history, marked by the repeated loss of their eyes after being isolated in dark environments. Geneticist Jaya Krishnan from the Oklahoma Medical Research Foundation notes, "It’s not just a story of loss in cavefish; there have been significant adaptations as well." While the disappearance of their eyesight continues to intrigue biologists, recent studies have shifted focus towards the unique adaptations that cavefish have developed to thrive in their subterranean habitats. These adaptations may even provide valuable insights into potential treatments for obesity and diabetes in humans. The question of why cavefish lost their eyes has sparked debate among scientists. Some previously suggested that the eyes simply degenerated over generations without causing disadvantages to the fish. However, evolutionary physiologist Nicolas Rohner from the University of Münster argues a more compelling theory: "Eyes are resource-intensive. It’s likely there is an evolutionary benefit to losing them if they are not needed." Research indicates that various mutations in genes related to eye development have resulted in the loss of sight among different cavefish populations. Krishnan emphasizes, "Different cavefish populations have lost their eyes through various genetic pathways." In contrast to their visual impairments, cavefish exhibit heightened other senses. Studies reveal that these fish can detect lower concentrations of amino acids compared to their surface-dwelling counterparts. Additionally, they possess an increased number of taste buds and a greater density of sensitive cells along their bodies, allowing them to effectively sense water pressure and flow in their dark, aquatic environments.