Ecology of a stream from upper Paraná River basin inhabited by Aspidoras fuscoguttatus Nijssen & Isbrüker, 1976 (Siluriformes, Callichthyidae)

Abstract

ABSTRACT Most information on catfishes of the genus Aspidoras has focused species kept in aquaria, in non-natural conditions. Biotic and abiotic parameters of environment inhabited by Aspidoras fuscoguttatus, associated ichthyofauna, as well as strategies involved in the successful occupation of different microhabitats in a first order stream, located in São José do Rio Preto, São Paulo State, were investigated. Data collection was monthly performed at three segments (headwaters, middle course, and mouth) from August 1999 to July 2000. The greatest values of water temperature, conductivity, turbidity, alkalinity, width, depth, and current velocity were obtained in the rainy season. Dissolved oxygen levels showed significant differences among three segments in all sampling months, except for September. Substrate composition was predominantly sandy, followed by silt and clay in middle course and mouth in rainy as much as in dry seasons. In headwaters a large increase of the sandy fraction occurred in the rainy season. In the marginal and aquatic vegetation 30 species of macrophytes and 5 of macroalgae were identified. The fauna included tadpoles of Anura and macroinvertebrates (Mollusca, Crustacea, Arachnida, and 8 orders of Insecta). A. fuscoguttatus was found throughout the entire stream in sympatry with 6 fish species. In middle course, cluster analysis revealed an association between A. fuscoguttatus immatures and low depth, suggesting a probable function of depth in that stage of ontogenetic development of catfishes. The results indicate that A. fuscoguttatus present plasticity in terms of microhabitat, including air breathing behavior in hypoxic conditions, previously unknown in genus Aspidoras.