Distribuição do ictioplâncton no Médio Rio Uruguai, Município de São Borja (Rs, Brasil)

Abstract

Large migratory species are generally of the highest commercial importance and are also those that suffer most from the effects of busbars and other anthropic impacts, however, there are few studies on these fish in less impacted environments and in Middle Uruguay. For the research were collected monthly during the reproductive period (October / 2015 to March / 2016). In the study, eight samples were collected at each point per month using a conical-cylindrical plankton trawl with a mesh of 500 μm. At the same time, the following water quality variables were analyzed: transparency, velocity, temperature, dissolved oxygen, electrical conductivity and water pH. The collected ichthyoplankton samples were fixed in 4% formalin. In the laboratory, the samples were screened and identified with the aid of a stereoscopic microscope. A total of 802 individuals were collected, most of them larvae. Spatially, it was verified that in the sampling point of São Borja there was a greater abundance of larvae of Schizodon nasutus, Prochilodus lineatus, Astyanax jacuhiensis, Bryconamericus stramineus, Pimelodus maculatus and Leporinus spp. A higher abundance of eggs and larvae was observed in early spring, mainly in November, which coincided with the increase in river level. In order to obtain the sample data, as well as abundance and standard deviation, the Univariate Analysis of Variance (oneway, ANOVA) was used. It is concluded that this stretch of the Uruguay River is an important nursery of fish including long-distance migratory species and that the reproductive period in the year 2015/2016 was concentrated in the spring when the river level was higher.