Abstract
This study aimed to analyse the composition and the ecological attributes of small-sized fish assemblages in four lagoons and in the main channel of Rosana Reservoir (SE Brazil). Fieldwork was carried out in September and November/2004 and January, March, May and August/2005. In each sampling station and period five manual throws were performed towards aquatic macrophyte stands, using a hand net (1.5 × 5 m; 0.3 cm of mesh size). The ichthyofauna collected was represented by 42 species, totalizing 3,424 individuals, 2,186 g in weight. The order Characiformes was dominant, mainly in the lagoons with low connectivity with the river. The main taxon (Importance Index) was Hemigrammus marginatus. Higher richness, abundance, biomass, diversity and lower individual mean length were observed in the lagoons, especially during the rainy period. Spatial segregation of some species was showed by the canonical correspondence analysis indicating the habitat complexity. The results validate the hypotheses that lateral lagoons have a prominent ecological role in the life cycle of juveniles and small fish and demonstrate how the connectivity river/lagoons may be important for assemblages maintenance.
Highlights
The construction of reservoirs has been intensified in developing countries during the last decades (Kennedy et al, 2003)
The role of lateral lagoons as a prominent ecological habitat for small freshwater fish has been widely demonstrated for the Neotropical region (Gafny et al, 2000; Barrella and Petrere Junior, 2003; Casatti et al, 2003; De Lima and Araujo-Lima, 2004; Pelicice and Agostinho, 2005, 2006, 2009)
The importance of the lagoon/river connectivity on the composition and the ecological attributes of fish assemblages is reinforced by the results of the present study
Summary
The construction of reservoirs has been intensified in developing countries during the last decades (Kennedy et al, 2003). In Brazil, these systems are especially designed to attend increasing demands for energy. 90% of the electric consumption is provided by hydropower plants The regional riverine systems have been transformed in large and spatially complex lentic (or semi-lentic) ecosystems (Soares et al, 2008), which influence the downstream stretches (Naliato et al, 2009). River regulation represents a major impact on fish assemblages and can drastically change the species composition and abundance. Some species cannot survive in the newly-created environment while others can become excessively abundant (Ahearn et al, 2005; Pelicice and Agostinho, 2008)
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