EFFECT OF YOUNG-OF-THE-YEAR WALLEYE (PERCIDAE, STIZOSTEDION-VITREUM) ON PLANKTON DYNAMICS AND WATER-QUALITY IN PONDS

To understand the impact of young-of-the-year (YOY) fish on food web d ynamics and water quality, we stocked larval walleye (9 mm TL) (Stizos tedion vitreum) in six experimental ponds using two fish densities (10 and 50 fish m(-3)) with three replicates. At high fish density, the a verage abundances of cladocerans and copepods and the Secchi depth wer e lower whereas abundances of rotifers and algae, gross primary produc tivity (GPP), pH and total phosphorus concentration were higher than a t low fish density. Fish impact on bacterial abundance, dissolved oxyg en, nitrogen and phosphorus concentrations, however, was not significa nt. The within treatment measurements of all variables except GPP were significantly different over time. Our results indicate that YOY wall eye predation at high density can affect plankton community by reducin g large zooplankton biomass and water clarity, and increasing phytopla nkton abundance. The impact of YOY piscivorous fish on plankton should be considered when biomanipulation is applied for improvement of wate r quality.