Threatened fishes of the world: Pimelodella kronei (Ribeiro, 1907) (Pimelodidae)

Abstract

Common names: Bagre cego (Port.), blind catfish (E). Conservation status: Endangered (some populations), vulnerable (others). Identification: Troglobite (fish species restricted to a subterranean habitat). Differs from the epigean catfish Pimelodella transitoria as a result of the regression of the eyes and pigmentation, and slightly shorter dorsal spines. Degree of pigmentation variable, some individuals with vestigial eyes. D I + 6 (rarely I + 7), A 12–15 (most frequently 13–14), P I + 8–9 (rarely 10), V 6 (rarely 7) (Trajano & Britski 1993). Mean maximum size 15.4 cm SL. May consist of two or more cryptic species resulting from parallel evolution. Photograph by Ivan Sazima. Distribution: Karstic area in the region of Iporanga (24°35′ S, 48°35′ W, Upper Rio Ribeira Valley, south-east Brazil. Known from five limestone caves in the Parque Estadual Turistico de Alto Ribeiro (PETAR): Areias system (including the type locality, Areias de Cima), Bombas resurgence and Corrego Seco Cave on the right margin of the Betari River, tributary of the Ribeira River, and the Alambari de Cima and Gurutuva caves on the left margin of the Betari River. These two sets of caves are isolated because the Betari River flows along a non-soluble, diabase dyke. Since troglobites rarely disperse via surface waters, these demes may correspond to independent events of colonization followed by isolation and parallel evolution in the subterranean habitat (thus, distinct phylogenetic species). Habitat and ecology: Headwater streams in caves, with rocky beds and many rapids intercalated with soft-bottom pools. Food scarce, energy input largely allochthonous. Areias and, to lesser extent, Bombas populations have been studied in detail since 1983 (Trajano 1989, 1991b). Blind catfishes are generalist feeders and opportunistic carnivores, preying on invertebrates. Their cryptobiotic habitats are poorly developed, probably due to the absence of predators in the caves. These blind catfishes are active predators that frequently explore the water column and surface and do not exhibit photophobia (Trajano 1989); this behaviour makes them very vulnerable to capture. Between 1983 and 1985 the population of Areias Cave was estimated at 900–1200 blind catfishes, with a low density (0.04 individuals m in sites where P. kronei concentrates) (Trajano 1991a). At these sites the blind catfishes are sedentary and possibly territorial. Aggressive dominance is based primarily on size and, to a lesser extent, on prior residence (Trajano 1991b). A hierarchy is maintained through individual recognition, probably by olfactory communication. Life-history: Precocial life history with infrequent reproduction, slow individual growth rates (0.1 cm month) and increased longevity (10–15 years) (Trajano 1991a). Threats: Deforestation (affecting energy input) and habitat destruction are under control at present. Excessive media reports on the PETAR and on the blind catfishes (which are the symbol of the PETAR), plus inadequate control of visitation, are presently the main threats. Overcollection in the 1970’s and disturbance by tourists in some caves are the probable main causes of a visible population decline. Sewage pollution, including pollution from detergents (that may destroy the fish olfactory epithelium) is another problem in some caves. The Alambari de Cima Cave population was nearly extinct due to pollution from mining activities. As this deme probably comprises a separate, cryptic species, it should be considered as severely endangered. Conservation actions: Visiting Areias Cave without a scientific purpose was prohibited by the National Environmental Council through Regulation no. 5 passed on 6 June 1987, but this is a poorly enforced regulation. Conservation recommendations: Visitation by tourists to all P. kronei sites should be prohibited, along with the effective control of visitation and activities upstream of the cave system (e.g. mining and deforestation). A reduction in media coverage would deflect public attention from blind catfishes and probably reduce clandestine visitation and catching; P. kronei localities should therefore not be widely publicised. Remarks: Troglobites in general are vulnerable to environmental stresses due to habitat restriction, reduced geographical distribution, relatively low tolerances of environmental fluctuations, small populations and precocial life histories, which make the recovery of declining populations a slow process. Several other Brazilian trogobitic fishes, which are poorly known, should also be considered to be potentially threatened.