Replacement of the Troglomorphic Population of Rhamdia quelen (Pisces: Pimelodidae) by an Epigean Population of the Same Species in the Cumaca Cave, Trinidad, West Indies

In 1926, Norman described the cave fish population in the Cumaca Cave of Trinidad, West Indies, as a new troglomorphic (blind /depigmented) genus and species, Caecorhamdia urichi, based on its reduction in eye size and pigmentation. Later studies indicated that this was just a cave population of the widely distributed epigean (surface, eyed/pigmented) catfish Rhamdia quelen. Beginning in the 1950s, a number of specimens were collected in the cave showing variability in eye size and pigmentation. In 2000 and 2001, we conducted field studies that included direct observation of individuals using infrared visual equipment (video cameras and night-vision goggles) and echo-sounders and also collected some individuals for behavioral research. We also examined all available specimens of the cave population that have been deposited in museums. Our results strongly suggest that the troglomorphic population has been completely replaced by the epigean one of the same species in as little as 50 years. We hypothesize that the most important reason for this replacement was the reinvasion of epigean individuals of R. quelen prompted by changes in precipitation regimes. Epigean individuals, because of their morphology, behavior, and ecological requirements, were well suited to outcompete troglomorphic individuals.