Avaliação de diferentes micro-hábitats para a reprodução de pexies no médio Rio Uruguai (Alecrim, RS)

Abstract

It is known that ichthyofauna uses during its life cycle the distinct micro-habitats present inside the mosaic of a river. However the importance that each of these environments has for each fish lifestages still aunknown for some basins, including for the Uruguay River. Based on that, the current work aimed to evaluate five different microhabitats for the reproduction of fish from the Middle Uruguay River, in the municipality of Alecrim, RS. For the research were performed monthly diurnal and nocturnal collections, during the peak reproductive period of the fish, from November 2015 to January 2016, totaling 120 samplings. The spatial distribution of collection points is situated in a stretch of approximately 4200 meters, being four points located in the Uruguay River (Municipality of Alecrim / RS): island, left bank, right bank and channel; and a point at the mouth of the tributary Arroyo Del Medio (Argentina). In all points, active collections were carried out from trawls using plankton net with conical-cylindrical format and using mesh size 500 μm. In each month, the following water quality variables were measured: transparency, velocity, temperature, dissolved oxygen, electrical conductivity, pH and river level. The samples collected were fixed in formalin 4%, and in the laboratory were identified with the help of a stereoscopic microscope. For the analysis, Variance Analysis (ANOVA), Tukey's a posteriori test and Pearson's Correlation were used. It was verified that there are significant differences for eggs and larvae (Tukey; P <0.05) in the different microhabitats, with emphasis on island, which had the highest larvae densities (Tukey; P <0.05). In relation to the shifts there were significant differences (Tukey; P <0.05), in which the nocturnal period presents the highest density / m³ of eggs and larvae. In relation to the months, it was verified that there is no significant variation of eggs and larvae in the samplings (P> 0.05). Five groups were identified at the genus level, twenty-six at the specific level, one at the family level and one unidentified. It was observed that the Barra Bonita point is characterized by the presence of Bryconamericus spp. And at point Island, the most abundant species were Pimelodus maculatus and Iheringichtys labrosus (Tukey; P <0.05). It is also worth mentioning the presence of large migratory species such as Pseudoplatystoma corruscans, Brycon orbignyanus and Salminus brasiliensis. According to the results, it is concluded that the point near the Island represents the site of higher incidence of total larvae, which characterizes this microhabitat as nursery of fish larvae in the early stages.