A subterranean population of<i>Garra barreimiae</i>(Teleostei: Cyprinidae) from Oman, with comments on the concept of regressive evolution

Abstract

The presence of a hypogean population of the cyprinid fish Garra barreimiae in the Jabal Akhdar mountains in Oman is noted. Specimens killed within a very short while of capture from the wild had very poorly developed optic lobes. The optic lobes of twelve fishes that died after four months in the light were nearly as large as those in epigean fishes so substantial brain tissue regrowth had occurred in that time. No development of the eye or optic nerve was detected. The eye remains in an embryonic condition close to the brain stem on the floor of the orbit. The concept of regressive evolution is considered to be invalid because it is unfalsifiable. The epigenetic effect of heterochrony is considered to be more appropriate vehicle to explain the convergent evolution of cavernicolous fishes.