Effect Of Fish Aquaculture And Feeding On Phytoplankton And Water Quality In Panjiakou Reservoir Enclosures

Field enclosure experiments were carried out in Panjiakou Reservoir, Hebei Province, People's Republic of China, from August, to October 2009, to study the impacts of fish aquaculture andsupplied fish food on phytoplankton and water quality. The results showed that in Panjiakou Reservoir the phytoplankton density was maintained at 2.6x10(6) cells L-1 in the experimental period, and the ratio of nitrogen to phosphorus was 112, so the reservoir was categorized as a "phosphorus-limited " system. The phytoplankton densities in enclosures with fish food only and with both fish stocking and fish food were significantly higher than those in the controlled enclosure and the reservoir water, and the phytoplankton density in the fish food only enclosure was significantly higher than that in the fish enclosures, while that in the bighead carp monocultured enclosure being the lowest. Bighead carp and carp could effectively restrain the growth of Cyanophyta, and change the dominant species of phytoplankton from Cyanophyta to Chlorophyta in the fish enclosures. Fish stocking with fish food significantly increased the turbidity, CODMn and total phosphorus. The concentrations of total nitrogen and dissolved oxygen in enclosures with fish food only and with both fish stocking and fish food were significantly lower than those in the controlled enclosure and the reservoir water. In the fish food only and fish stocking with fish food enclosures, significant positive correlations between phytoplankton density and the turbidity, CODMn, total phosphorus were found.