Effects of a small planktivore (Pseudorasbora parva: Cyprinidae) on eutrophication of a shallow eutrophic lake in central China

An enclosure experiment was performed in Lake Yuehu, central China, to assess the effects of a gradient of Pseudorasbora parva biomass on eutrophication state parameters, from May 15 to June 14, 2004. Experimental enclosures were placed into the lake and four treatments were conducted: Control (no fish), low fish (16.5 g m(-3)), medium fish (55 g m(-3)), and high fish (110 g m(-3)). The experimental fish were an average total length of 78 +/- 7 mm (mean +/- standard deviation) and an average weight of 5.5 +/- 1.5 g (mean +/- standard deviation). In general, fish increased Secchi disk transparency (SD) and reduced chlorophyll a and total phytoplankton cells, especially in the medium and high fish treatments. No significant effect of fish on total nitrogen (TN) and total phosphorus (TP) was observed. Relatively higher SD, and lower TN and TP were observed in the medium fish treatment as compared to other fish treatments. Effects of fish biomass on chlorophyll a and total phytoplankton cells were not significantly different between the medium and the high fish treatments. Based on the observed eutrophication parameters and fish mortality, the current experiments suggest that maintaining a 55 g m(-3) biomass of P. parva may be helpful for controlling eutrophic state in the studied lake. Further studies are needed to extrapolate the current results to the whole-lake management decisions