Fish assemblage of the Santo Anastácio reservoir (Ceará state, Brazil)

Abstract

Located on the campus of the Federal University of Ceará, the Santo Anastácio reservoir is a hypereutrophic ecosystem which has been the object of ecological research over the last four decades. The present study describes the current fish assemblage of the reservoir and discusses variations observed since 1977. Fish were sampled monthly between October 2009 and March 2010 using gillnets and seine nets in three zones. The fishes were identified, measured (standard length; cm) and weighed (g) to evaluate aspects of structure (richness, diversity, biomass and size) and spatial distribution of the icthyofauna in the reservoir. The fish assemblage in the reservoir was found to have changed considerably over time. Several fish species reported in earlier studies, such as Leporinus friderici, Eigenmannia virescens, Serrasalmus brandtii and Betta sp., were not registered in our samples from 2009 and 2010. The predominance of species tolerant to hypoxic and eutrophic ecosystems, such as Oreochromis niloticus, Poecilia vivipara, Poecilia reticulata and Hoplosternum littorale, as well as the scarcity of Prochilodus brevis and Hypostomus pusarum, illustrate the influence of environmental conditions and the introduction of exotic species on fish richness. The icthyofauna of the Santo Anastácio reservoir consisted of relatively few species. The sampled zones did not vary significantly with regard to community structure. Despite the small number of species, the resevoir’s population of O. niloticus is exploited by local subsistence fishermen