EFFECTS OF SILVER CARP DENSITY ON ZOOPLANKTON AND WATER-QUALITY - IMPLICATIONS FOR EUTROPHIC LAKES IN CHINA

We examined the responses of zooplankton community, water transparency , chlorophyll a and nutrients to manipulation of density of silver car p (Hypophthyalmichthys molitrix) in an one-way factorial experiment us ing enclosures placed in Donghu (East Lake, 30 degrees 33' N, 114 degr ees 23' E), located in Wuhan, P. R. China. Enclosures (18.75 m(3)) wer e treated with four silver carp densities, 0, 81, 225, 485 g/m(2). Tot al zooplankton abundance (excluding nauplii and rotifers except for As planchna sp.) and the mean size of dominant cladoceran species were si gnificantly greater in enclosures with 0 and 81 fish densities than th ose in enclosures with 225 and 485 fish densities. Water transparency also improved significantly when silver carp densities were 0 or 81 g/ m(2). We did not find significant effects of silver carp density on ch lorophyll a, total phosphorus, or total nitrogen concentrations. We co nclude that by reducing planktivorous fish to below the current densit y (190 g/m(2)), the zooplankton community can be shifted from the domi nance of small-bodied Moina sp. to dominance of large-bodied Daphnia s p. Further, the water clarity can be increased.