Quantitative analyses of stomach
contents indicate Prochilodus platensis depends on detritus rather than microorganisms for its nutrition. Chemical data suggest that this detritus is of a different origin than previously supposed.
The development of large impoundments along the Parana river, particularly on the Superior section, with fifteen large dams having a capacity over 25 000 MW, has had important hydrological and ecological impacts on the lower reaches. The important retention of the suspended solids by the dams has caused a significant reduction of P concentrations. With river impoundment and water eutrophication, cyanophiceae currently dominate during spring and summer, with brief but dense blooms of Anahaena spiriodes and Microcystis aeruginosa. Many fishes of the Superior Parana have been dispersed downstream as the Itaipu reservoir covered the Guayra falls, the natural barrier for these fishes.The most important effects of Superior Parana dams are related to the changed hydrological regime in the alluvial Middle and Lower reaches. This floodplain plays an important role in the bioproductivity of the river. Fisheries production depends to a high degree on the relationship of the river and its alluvial valley, where the alevines and small fishes of migratory species develop after spawning. During falling river levels the waters carry large quantities of organic matter, floating vegetation, important amounts of plankton and fishes from the alluvial plain to the river. Before the dams, the river defined two subsystems which were joined for about six months during the flood season and effectively isolated during low water periods.Since the commencement of river impoundment and flow regulation, the river ecology has begun a sequence of changes especially within the alluvial reaches.
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