RECENT CHANGES IN FISH ASSEMBLAGES OF A LENTIC-LOTIC SYSTEM IN CENTRAL ITALY (LAKE POSTA FIBRENO, LATIUM), WITH REMARKS ON SALMONIDS SITUATION

Fish assemblages of a lentic-lotic hydrographic system in Central Italy (Latium), undergoing alterations in streams riparian canopy and lake submerged vegetation, were investigated from September 2004 to December 2007. Changes in the composition of ichthyofauna of the system were highlighted, providing original information on presence and distribution of taxa within the water system. Qualitative data were collected by means of electrofishing in the water courses and by frequent fishermen’s gears control, day and night scuba-diving and snorkeling visual census in the lake area..Quantitative data on salmonids derived from 1-2 electrofishing catches in the four streams of the system. An increase of six taxa emerged from the comparison with previous available data, with a total number of 17 taxa recorded. All recently appeared taxa are cyprinids or poecilids, indicating a warm-water species invasion of this hydrographicbasin in the last two decades. Noteworthy is the occurrence of five species of European interest (Habitat Directive 1992/43/CEE), plus the endemic taxon S. fibreni (astoundingly not included in the Directive), making this small system a relevant conservation challenge to deal with. Our data outline a changing process in the fish assemblages of this system with significant qualitative alterations. Quantitative investigations showed low numbers of salmonids (Salmo trutta macrostigma and Salmo fibreni), with marked differences among streams. Thus, further essential observations, in progress at present, are needed.