Effects of Polyculture and Manure Fertilization on Water Quality and Heterotrophic Productivity in Macrobrachium rosenbergii Ponds

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Abstract
Water quality effects of high densities of silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella, and water hyacinths Eichhornia crassipes in semi‐intensive pond culture of prawns Macrobrachium rosenbergii were examined. Additional effects of isonitrogenous additions (8 kg N˙hectare−1˙week−1) of dried chicken manure and chicken broiler feed were evaluated. Excretion, grazing, and sediment resuspension by the carps stimulated phytoplankton productivity and turnover rates of microplankton, led to high early‐morning dissolved oxygen (DO) concentrations, and, in the ponds fed manure, increased phytoplankton biomass. Removal of phosphorus from the water by water hyacinths led to reduced chlorophyll‐α concentrations, primary productivity, and microplankton turnover, and to low morning DO concentrations: In hyacinth ponds fed chicken broiler feed, there were large percentage fluctuations in phytoplankton biomass. Additions of manure stimulated autotrophic productivity about 3.0 times, and total microbial productivity about 4.6 times, more than additions of chicken feed. Biological control of phytoplankton dynamics and maintenance of DO concentrations at high phytoplankton standing crops by Chinese carps appears a viable alternative to present methods of water quality control in semi‐intensive prawn aquaculture.