Habitat structure and stream fishes in a pasture basin, Sao Paulo, Brazil.

Abstract

Four stream stretches (sites 1-4) in a pasture area of the northwestern Sao Paulo state were studied, aiming to examine the composition and quantitative structure of the ichthyofauna and investigate its relation with habitat features. Fishes were collected during the three most representative months of the dry and wet periods by one electrofishing pass in each month. Chemical water quality analysis showed good conditions in all sites, whereas physical habitat integrity analysis showed poor conditions to the sites 2 and 3 and fair to the sites 1 and 4. Twenty seven fish species were collected for a total of 1241 specimens and 5,1 kg. The quantitative structure of the ichthyofauna revealed closer association with habitat structure than to seasonality because sites 1 and 2 were split from sites 3 and 4, independently of the season. According to the canonical correspondence analysis, the higher abundance of Gymnotus carapo Linnaeus, 1758 in the sites 1 and 2 was associated to marginal vegetation abundance, the abundance of Piabina argentea Reinhardt, 1867 in the site 3 was explained by the habitat volume, and the abundance of Hypostomus nigromaculatus (Schubart, 1964) in the site 4 was related to the rocky substrate predominance.