Fish-macrophyte association as a low-cost strategy for wastewater reclamation

Abstract

Water hyacinth Eichhornia crassipes was harvested every 2 weeks, from fish-introduced limnocorral installed in a sewage-fed pond, and changes in water and sediment quality as well as aquatic food chain were compared with that of limnocorral infested with hyacinth but without fish. Harvesting of water hyacinth resulted in greater removal of orthophosphate (OP), soluble reactive phosphate (SRP), total phosphate (total-P), ammonium-N, nitrite-N and nitrate-N in the water phase as well as total- and available-N and P in the sediment compared to that of unharvested system. Counts of heterotrophic, denitrifying and phosphate solubilizing bacterial population were markedly higher in presence of water hyacinth regardless of fish introduction. Periodic harvest of Eichhornia caused the shifting of dominance of Euglenophyceae in the beginning to Chlorophyceae at termination, when zooplankton population represented by rotifers and copepods declined. It appears that Eichhornia harvesting resulted in gradual induction of grazing food chain with heterogeneity in the planktonic community as well as better water quality required for fish growth.