Predatory impact of the mosquitofish (Gambusia holbrooki Girard) on zooplanktonic populations in a pond at Tenuta di Castelporziano (Rome, Central Italy)

A study of a permanent pond located in a nature reserve in Central Italy was carried out over two periods (1985-87; 1995-98) to determine the structure and dynamics of planktonic biocoenosis. The composition of the zooplankton community was quite different in the two periods of study: in the first period, rotifers, small-bodied cladocerans and larval copepods were the dominant groups; in the second there was a shift from rotifers and microcrustaceans to dominance by large-bodied Daphnidae and adult copepods. The possibility is stressed that Gambusia holbrooki, present in 1985 and absent in 1995, may be responsible for the changes in the planktonic community.