Introdução e impactos da tilápia do Nilo (Oreochromis niloticus) sobre as assembleias de peixes nativos na bacia hidrográfica do Tarumã-açu

Abstract

ABSTRACT The introduction of exotic species and human actions are the problems that most impact the Earth’s biodiversity. Nile tilapia (Oreochromis niloticus) is the most cultivated fish species in Brazil, and has been illegally introduced in the central Amazon. Escape to the natural environment has been occurring and specimens are already being found in several streams of Manaus-AM. This study aimed to investigate the introduction of the exotic species in the Tarumã-açu River basin (Manaus, Amazonas, Brazil), one of the main tributaries of the Rio Negro, which flows from several streams impacted by human activities, in order to evaluate possible impacts on the structure of native fish assemblages. The study was carried out during the dry season. A total of 427 specimens were captured, distributed in 5 orders, 19 families, and 40 species. The order Characiformes was the most representative with 23 species, followed by Siluriformes with 6 species. The most diverse families were the Cichlidae and Hemiodontidae, with 9 and 5 species, respectively. The species with the highest relative abundance were Hemiodus immaculatus, and Oreochromis niloticus. The diversity estimated by the Shannon-Wiener index was considered low for the five sites sampled. The Pielou equitability index (J) indicated homogeneity for four locations, except for the Cachoeira Alta do Tarumã stream, where the dominance estimated by the Berger-Parker index was equal to 0.90. The environmental parameters OD, pH, electrical conductivity, ºC, water transparency, and phosphorus showed significant variations due to anthropic actions. Ammonia and nitrite presented values within the predicted by CONAMA resolution 357/2005. Mantel's test level does not indicate the influence of Nile tilapia and/or environmental variables on the fish assemblages. However, the exotic species was captured at the mouth of the Gigante stream, less than 500 meters from the Rio Negro and this species was the second most frequent in the samplings. Keywords: Introduction, Nile tilapia, Exotic Species, Impacts, Tarumã-açu Watershed.