Abstract

The aim of this study was to characterize zooplankton community composition atPadre Azevedo reservoir and to determine their relationship to water quality, following a gradient of distance from an aquaculture site. Monthly samples were collected by filtering 15 L of water with a plankton net (45 mm mesh size), and fixing it with a 4% formaldehyde solution saturated with sugar. Zooplankton community composition was dominated by rotifers, mostly Keratella tropica, Brachionus havanaensis andBrachionus calyciflorus, and Cyclopoida copepods (mostly nauplii). These species are typically associated to eutrophic environments. During the dry season, a higher diversity of rotifers was observed, whereas density of cladocerans increased during the rainy season. Sampling station P₄, the most distant station from the culture site, showed lower zooplankton densities. The most distant sampling station showed higher water quality, as particularly during the dry season, suggesting that aquaculture negatively affects water quality at nearby areas, as evidenced by zooplankton composition.

Key words: Environmental impact, fish culture, net cages, zooplankton.