The phototactic behaviour of three Copionodontinae (Trichomycteridae) catfish species (two troglobites and one epigean) from Chapada Diamantina was studied in order to detect modifications related to isolation in the subterranean environment. Differences in response under different luminosities were detected and, unlike other cavefish, Copionodontinae cave species have shown to be more photophobic than the epigean syntopic to them. The troglobitic Glaphyropoma spinosum is the most photophobic, presenting this behaviour under all light intensities, and more homogeneous regarding morphological characters. It suggests that this population is probably isolated for a longer time in the subterranean environment compared to Copionodon sp. n., the other cave species, which is only photophobic under low light intensities. The indifference to light exhibited by the epigean species C. pecten could be an answer to a recent predation pressure, an ecological aspect, and perhaps this character-state is under fixation in this population. There are also evidences that the skin has a relevant role in the perception of light for the Copionodontinae species.