Fig. 12. Reduction of the retina and central regions of the visual system in cave fish. (A) Eye loss in cave populations of Astyanax mexicanus that have been isolated for approximately 1 million years. The photograph shows one eyeless cave fish (foreground) and two fish from closely related surface-dwelling populations. (B) Reduction in the relative size of the brain regions associated with visual processing in fish species living permanently in caves. (i) Amblyopsis spelaea, a fish species living exclusively in caves. (ii) Chologaster agassizi, a fish species occasionally found in caves but also in surface environments. Adapted from Poulson and White (Poulson and White, 1969). Photograph by R. Borowsky, reproduced with permission.