Water quality and plankton populations in an earthen polyculture pond

Abstract

This work was carried out during one year in a fish pond to evaluate the effect of water quality in a plankton community according to the adopted management. High densities of Euglenophyceae, Chlorophyceae and Cyanobacteria were associated with high nitrate levels (1 to 210 mg.L-1). Cell densities of Cyanobacteria over 90 ind.m³ × 10³ (85.5%) occurred when nitrate concentrations approximated 210 mg.L-1, total phosphorus less than 160 mg.L-1 and temperature above 25 °C. High density of Rotifera was associated with high density of Cyanobacteria (December). Only Trichocerca sp. among the Rotifera species was constant in all sampled sites, whereas Diaphanosoma birgei, ranging between 4 and 342 ind.L-1 (0.7 and 2.4%) during the study period, was the most representative among the Cladocera species. Results show that water quality management in the fish pond had a direct influence on the plankton population due to the shallowness of the environment, large nutrient discharges through feed, fertilizing, fish waste. In fact, they contribute towards the appearance of undesirable plankton organisms.