A review of the zooplankton studies in Paraguay's freshwater environments

This study is a review of the zooplankton studies in Paraguay, where two of South America's large hydrographic basins are found those of the Paraguay and Parana rivers. After exhaustive searches, twenty-two published studies were found, with three of them being developed by national researchers, while all the others were carried out by foreign researchers or with their collaboration. The first studies were done between 1905 and 1936, involving field studies with taxonomy and ecological data and an experimental study testing the influence of temperature and dissolved oxygen on zooplankton. The studies resumed in 1960, presenting mainly data for rotifers, cladocerans and copepods in the plankton community, including taxonomic inventory, richness and species diversity, community composition, beta diversity, abundance and dominance. Most of the studies were carried out in the Paraguay River basin and in the limnetic region of lakes and reservoirs. Some copepod species were typical of lentic or lotic environments and low or high trophic conditions, Overall, 154 zooplankton species were registered (70 rotifers, 51 cladocerans and 33 copepods), with high diversity for Brachionidae and Lecanidae (rotifers), Chydoridae (cladocerans) and Cyclopidae (copepods). The zooplankton richness recorded in Paraguayan territory is lower than in larger and more explored South American countries such as Argentina and Brazil, but similar to found in other countries of a similar size. Moreover, there are few scientific centers and there is low funding for research, which are important factors for the development of scientific knowledge. Planktonic protozoan communities, functional diversity or molecular analyses of zooplankton were the main gaps in the zooplankton studies. Few studies for the zooplankton were published from Paraguay country and more are necessary, close to the main channels of the Paraguay and Parana rivers, in the Itaipu reservoir and far from these rivers, inside the country, where few or none studies were made.