Efeito do óxido de cálcio sobre variáveis limnológicas em viveiros de criação de Piaractus mesopotamicus (pacu) e Colossoma macropomum (tambaqui)

The objective of the study was to evaluate the effects of calcium oxide on the water quality of two ponds (V1: with calcium oxide and V2: without calcium oxide) populated with pacu (Piaractus mesopotamicus) and tambaqui (Colossoma macropomum), during the draught period from July to October 1997. Calcium oxide influenced greatly the conductivity, transparency, pH, alkalinity, bicarbonate, carbonate and orthophosphate of the water pond. Inlet water carried into the fishponds high levels of chlorophyll-a, orthophosphate and nitrogen compounds. Calcium oxide applied on the sediment of empty V1 resulted in reduced values of magnesium, potassium, and copper concentrations. Phosphorus and iron levels were lower in the sediment of pond V1 when compared to those registered in V2. Calcium oxide applied on water pond favored culture conditions, reduced transparency and increased alkalinity. In general, the concentrations of nitrogen compounds in the pond were reduced, making available the phytoplankton development. The application of liming materials when necessary keeps good records to the improvement of water quality and overall pond productivity.