Comunidade zooplanctônica e estado trófico de um reservatório do semiárido paraibano com piscicultura intensiva em tanques-rede

Abstract

The study aimed to evaluate the impact of fish farming in cages in the water quality and the possibility of the use of the zooplankton community, as an indicator of these impacts, characterizing the effects caused by the increase of nutrients after this activity in the water body. The study area was the Carneiro dam, Jericó, Paraíba. The variables were sampled monthly (Jun-Nov/2009) at three stations: the amount of tanks of intensive cultivation of fish next to and downstream of the tanks, along the water column in vertical profiles, following the rate of extinction of light (100%, 1% and 0% of light). The trophic state index of Carlson (1977) modified by Toledo Jr. et al. (1983) was used to determine the trophic level of the dam. The zooplankton samples were accomplished using a bucket (10L), filtered with a plankton net (mesh 68 mm) and fixed in neutral formalin with sucrose. The influence of fish farming in cages on the density fluctuations of the zooplankton community and water quality was not clearly detected. The results showed rain events exerting a negative influence on water quality and zooplankton, contributing to the increase of nutrients (N and P), algal biomass and consequently the trophic condition of the ecosystem, a result confirmed by the modified Carlson EIT, classifying it as eutrophic. The phylum Rotifera was the most representative in richness and density followed by Copepoda and Cladocera. The density showed an increase during the dry season and eutrophic condition to determine the presence of species, with dominance: Brachionus calyciflorus, Filinia opoliensis, Ceriodaphnia cornuta, copepod nauplii and copepodites cyclopoides.