Abstract
This study was conducted in the Meia Ponte River basin, which is located in the Cerrado biome. The objective was to describe the structure of fish assemblages and to evaluate the results with the regard to the position of the tributaries (sampling stations) along the basin. This basin drains 35 municipalities of Goiás State. Springs of the Meia Ponte are located in the district of Itauçu (GO), in the Serra dos Brandões. Two sampling were conducted, one in the rainy season (March/2001) and another in the dry season (August/2001). Thirty sampling sites in tributaries and one in the channel of the Meia Ponte River, in its upper course, were selected to capture fish with dipnets (3 mm mesh) during one hour, along 100-m stretch. Sampling periods (season; rainy and dry) and the categorization according to the distance of the sampling station from the mouth of the Meia Ponte River (position; upper, intermediate and lower) were used to evaluate differences in fish assemblage structure, summarized by a detrended correspondence analysis (DCA), applied on the abundance data matrix, squared root transformed, to eliminate the effect of abundant species. The first two axes were retained for interpretation (eigenvalues = 0.35 and 0.24, for axis 1 and 2, respectively). The two-way ANOVA (factors seasons and positions) identified significant differences (p <0.05) in score averages for axis 1 and 2, for both factors. These results suggest significant differences in fish assemblage structure in the Meia Ponte River basin for the seasons (rainy and dry) and positions (upper, intermediate and lower) studied, in spite of the short spatial scale. These findings demonstrate a great ichthyofauna heterogeneity in the uppermost part of the Paraná River.
Highlights
The identification of environmental gradients structuring fish assemblages is one of the main challenges of stream ecologists (Gilliam et al, 1993). Hughes & Gammon (1987) stated that physiographies of the basins are the environmental parameters traditionally used to explain ichthyological regions, and these are large areas where similar fish assemblages are found
Grenouillet et al (2004) report that species richness of streams, within a hydrographic basin, may be influenced by local habitat conditions and stream order along a watershed. The latter is dependent on stream geographical position within a basin
Other studies associate the structure of fish assemblages with the historical formation of a hydrographic basin (Williams et al, 2003), different habitats and/or microhabitats (i.e. MarshMatthews & Matthews, 2000) and the increase in water volume and shelter availability as well (Araújo-Lima et al, 1998; Jackson et al, 2001)
Summary
The identification of environmental gradients structuring fish assemblages is one of the main challenges of stream ecologists (Gilliam et al, 1993). Hughes & Gammon (1987) stated that physiographies of the basins are the environmental parameters traditionally used to explain ichthyological regions, and these are large areas where similar fish assemblages are found. Grenouillet et al (2004) report that species richness of streams, within a hydrographic basin, may be influenced by local habitat conditions (local factors) and stream order along a watershed. Other studies consider abiotic (physical characteristics, geology and hydrology) and biotic (predation) factors, human occupation, agriculture and urbanization. All these induce alteration in habitats and, in the biota along a water course (Balon, 1993; Penczak et al.,1994; Moyle, 1995; Wiens, 2002; Solé et al, 2003)
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