POLYCULTURE OF CHINESE CARPS AND PRAWNS AT COMMERCIAL DENSITIES AND REDUCED FEEDING RATES I. WATER AND SEDIMENT MICROBIAL ECOLOGY

The ecology of water and sediment microbial communities was examined over a 28‐week period in semi‐intensive prawn monoculture ponds and fish/prawn polyculture ponds stocked with commercial densities of silver and grass carp but fed at 50% and 1% of control feeding rates. Fish polycultures at reduced feeding rates had little effect on phytoplankton biomass parameters (concentrations of ATP, chl a), total nitrogen and phosphorus concentrations (TN, TP) and total organic carbon (TOC) during the experimental period. However, fish polyculture ponds fed at reduced rates had significantly increased rates of primary production, microbial DNA synthesis, dissolved organic carbon (DOC) concentrations, and surface sedimentary oxygen consumption rates compared to controls. High rate plyculture ponds fed at one‐half (20 kg·ha ‐1 ·d ‐1 ) the control monoculture ponds (40 kg·ha ‐1 · d ‐1 ) had two times (2X) lower suspended organic matter (SOM) concentrations at 13 weeks, lower surface sediment ATP concentrations at 9 weeks, less within‐pond variability in surface sediment ATP concentrations, and higher sedimentary respiration rates than controls. Polyculture ponds fed at 0.4 kg·ha ‐1 · d ‐1 had 3X less SOM than controls but had sedimentary respiration rates similar to the high rate polyculture ponds. In short, fish polycultures in intensive prawn aquaculture ponds combined with reduced feeding rates may be a simple solution to the pervasive problems of water quality control, benthic reducing conditions and decreased prawn growth characteristic of semi‐intensive aquaculture ponds under continuous cultivation.