Composição, estrutura e fatores determinantes da ictiofauna de um reservatório neotropical: Cachoeira Dourada, Goiás - Minas Gerais, Brasil

Abstract

This study aimed to characterize the composition and structure of the ichthyofauna of UHE Cachoeira Dourada (15 º 27'S and 44 º 41'W), which has about 74km2 (average) of flooded area. Therefore, we selected two points (P1 and P2) for fish sampling, in which were installed batteries of 10 gill nets, each 50m long, 2.0m high, with meshes respectively, 2.0cm to 6.5cm between adjacent knots. These points were sampled from February 2007 to January 2008. In September 2007 we added a point (P3) upstream of the reservoir in an oxbow lake, which was also sampled using gill nets. The nets were left in water for 24 hours and the harvesting was done every 12 hours. In addition, physical and chemical data were collected in both surface and bottom on 05 points distributed along the reservoir, and 01 immediately downstream of the dam, in order to characterize the system. The limnological parameters values were similar for each of the points, and did not show the typical gradient from the river towards dam. There was no vertical stratification of temperature or oxygen. The seasonal variation of limnological parameters (between the rainy and dry months) was greater than the longitudinal variation within each period. These facts suggest that the small size of the reservoir, its shallowness and non-dendritic shape closes its limnological behavior to that of a lotic system. A total of 1988 specimens and 326.16 kilograms of fish were captured. These were divided into four orders, 15 families and 35 species. Six introduced species accounted for 32% of the catch in numbers and 29% of the catch in biomass. The assemblages at points P1 and P2 were adjusted to the logarithmic model of rank-abundance. Simpson's diversity was high (> 70%), except during the dry season in P2. The most abundant species in the three points, in decreasing order of importance, were Pimelodus maculatus, Satanoperca papaterra, Pinirampus pirinampu, Cichla piquiti, C. kelberii, Astyanax altiparanae, Schizodon nasutus and Serrasalmus maculatus. The seasonal variation in abundance correlated with pH and water transparency. Among the reproductive guilds, four long-distance migratory species were the most abundant in terms of numbers and biomass. The group with the largest number of species was the guarders, which was also the second most abundant in numbers and biomass. Carnivores dominated in numbers and biomass, followed by piscivores and benthic-feeders. This fact, combined with the low abundances of illiophagy and herbivores, suggests that the energy used by the fish fauna is of allochthonous origin, similar to lotic environments. Correspondence of species with different points was related to habitat heterogeneity, availability of food resources and biotic interactions such as predation and competition.