| Summary: | The evolution of the ichthyofauna of Lake Lugano (Lago di Lugano) during the past 120 years is characterized by the introduction of eight new fish species and by the possibly natural addition of the blenny ( Blennius fluviatilis ) in recent years. Introduced Salmonids such as charr ( Salvelinus alpinus ) and whitefish ( Coregonus sp. ) have established strong populations during the first half of this century, but have declined drastically thereafter. Likewise, the population of the native shad ( Alosa fallax lacustris ) has diminished significantly. A hydroacoustic survey of the pelagic fish stock of Lake Lugano in 1989 revealed the presence of a dense bleak ( Alburnus albidus ) population at 0 to 14 m depth. No other fish were found to be present in the pelagic zone. Oxygen and temperature distributions seem to confine the bleak to the uppermost layer in summer. In winter, very few fish were located by echosounding. Growth of bleak and roach ( Rutilus rubilio ) was difficult to interpret since data for comparison are lacking. Growth of perch ( Perca fluviatilis ) in the littoral zone was found to be slower than in other eutrophic lakes, for no obvious reason. Possible ways of restructuring the pelagic fish community are discussed.
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