Introduction of exotic fish into a Mediterranean lake over a 90-year period

The impact of exotic species is a neglected, worldwide ecological problem, particularly for freshwater fish. Examples of historical changes in souther n Europe due to fish introduction are rare. Lake Banyoles, the second large st lake of the Iberian Peninsula, has suffered a long history of fish intro ductions. We reviewed the historical changes in the fish assemblage and ass essed its current state in a field study. Before 1910, only five or six nat ive species were present. During this century up to 12 exotic species were introduced, leading to the apparent loss of two native species (three-spine d stickleback Gasterosteus aculeatus and, possibly introduced several centu ries ago, tench Tinca tinca) and the decline of three others (eel Anguilla anguilla, chub Leuciscus cephalus, and barbel Barbus meridionalis). The cur rent fish assemblage is dominated by exotic species, particularly the large mouth bass (Micropterus salmoides) and the pumpkinseed sunfish (Lepomis gib bosus) in the littoral zone and roach (Rutilus rutilus) in the pelagic zone . The only native species still common nowadays is the freshwater blenny (S alaria (= Blennius)fluviatilis).