Toxicity of lead to freshwater invertebrates (Water fleas; Daphnia magna and Cyclop sp) in fish ponds in a tropical floodplain

Acute toxicity of Pb to the water flea; (Daphnia sp) and Copepod, (Cyclop sp) both important component of zooplankton diet of fish was determined by static assay. A positive relationship between percentage mortality and exposure concentration was found in all tests. Mean 24-h LC50, 48-h LC50 and 96-h LC50 values were 2.51 +/- 0.0.04 mg l(-1), 1.88 +/- 0.06 mg l(-1) and 1.65 +/- 0.19 mg l(-1) for Daphnia spp and 3.11 +/- 0.03 mg l(-1), 2.97 +/- 0.05 mg l(-1) and 2.61 +/- 0.09 mg l(-1) for Cyclop spp, respectively. For all tested species did the LC50 values decrease with time; the decrease was more marked for Daphnia spp. Observed symptoms include spiral movement followed by change of body colour to white and rapid disintegration of the skin. The Daphnia spp. appear to be more sensitive to Pb poison than Cyclop spp. The results showed that concentrations of Lead (Pb) in excess of 0.19 mg l(-1) and 0.30 mg l(-1) can be potentially harmful to Daphnia magna and Cyclop spp respectively.