INTERACTION OF COMMON CARP WITH AQUATIC WEEDS IN ARGENTINE DRAINAGE CHANNELS

Two different densities (1000 and 2000 fish ha(-1); average weight 20 g) of common carp, Cyprinus carpio L., were stocked into an Argentine drainage channel, following mechanical removal of die vegetation. In a second experiment lar ger fish (average weight 260 g) were stocked at 500 and 1000 fish ha(-1). In this experiment vegetation was not remov ed prior to stocking. Common carp significantly reduced growth of the dominant submersed weeds present (Chara contraria A. Braun ex Kutz; Ru ppia maritima L.) in both experiments, as compared with the untreated controls. Three months after the introduction of the smaller fish the reduction of plant biomass ranged from 40 to 86% of control plots. Lar ger fish completely destroyed all submersed weed growth within 4 month s. The common carp stocking elevated water turbidity by up to 10 times that of control plots, by stirring up of sediments during their feedi ng activities. Direct herbivory was also observed.