Aspectos ecológicos de uma população de bagres troglófilos do gênero Ituglanis Costa & Bockmann, 1993 do centro-oeste de Minas Gerais, Brasil

Abstract

The caves are among the least known and most threatened habitats, with remarkable features, such as a tendency to permanent darkness and environmental stability. The absence of light implies in absence of photosynthesis, leading to a framework of oligotroph, making the caves totally dependent on the nutrient intake from the epigean environment. For that matter, it is essential to understand the relationship of the species with the subterraneanenvironment, for a better understanding of the interaction of the populations with these environments, usually short in resources. Therefore, this work aimed to study population and food aspects of the troglophile catfish genus Ituglanis Costa &Bockmann, 1993 found isolated in a small watercourse, known as Locad’Água stream, in the municipality of Pains (center-west of Minas Gerais). This drainage is part of an atypical system, connecting, at epigean environment, two caves, one upstream (Locad’Águade Cima) and one downstream (Locad’Águade Baixo). It is noteworthy that this drainage appears in the cave from upstream (with autogenic characteristics) and disappears at a sinkhole at the end of the cave downstream. Two studies were carried out separately. In the first, was conducted a mark-and-recapture work, where were investigated the population sizes and densities, the population structure in size classes and individual movements. The results of the study indicate to a relatively small population, ranging from375-550 individuals (density: 29,4-43,1 ind/m2) in the Locad’Água de Cima cave, 600-950 individuals (density: 11,1-17,6 ind/m2) in the Locad’Água de Baixo cave and 950-1350 individuals (density: 13,1-18,7 ind/m2) in the whole system. The slightest variation in the fishes sizes in the Locad’Água de Baixo cave indicate a higher environmental stability in this cave. Sedentary behavior was also observed in the population, and no displacements of fish between the caves were registered. In the second study was investigated the diet and condition degree of this population on the basis of data collected in the years 2010 and 2018. Were analyzed stomach contents of 83 fishes, being 42 individuals collected in 2010 (29 in the epigean stretch and 13 in the Locad’Água de Baixo cave) and 41 in 2018 (20 in the Locad’Água de Cima cave and 21 in the Locad’Água de Baixo cave). The proportion of individuals with empty stomachs are low. The results of the analyze of the gastric contents indicates that Ituglanis sp. is a carnivorous(invertivorous) generalist species, which although mainly preys on insects (especially larval forms), varied its diet according to the availability of resources in the different environments and years of collecting. The results of this study pointed to a population completely adapted to the system and the subterraneanenvironment, showing sedentary behavior and good food conditions, even after a period of sharp drought in recent years, which leaded to a dramatically decrease on the water volume in the system and allegedly has been maintaining the population isolated in the caves.