L’esotica Oncorhynchus mykiss (Wallbaum 1792) nel bacino idrografico di un corpo idrico mediterraneo: fattori che ne favoriscono l’insediamento ed i rischi associati

One case of spawning of the introduced Oncorhynchus mykiss was studied in a Mediterranean freshwater ecosystem, in Northern Italy (Alserio lake watershed, Lombardy, IT). Two contiguous watercourses, showing different habitat features, were colonised by the same genetic stock, as indicated by genetic analysis which individuated an affinity with the native Shasta Mount-Mc Cloud strains system (Siskiyou, CA), witnessing the rusticity of the invading populations. The two populations showed different behaviour related to different environmental conditions, demonstrating high plasticity and resistance to the abiotic constrains. In particular, they resulted resistant to strong hydrological variations even at juvenile stages, contrarily to what detected in other regions. The  two populations showed an anticipation of the reproductive phase in Autumn, contrarily to what commonly occurred in the native range. The study thus suggests a potential invasiveness, linked with negative effects on the receiving ecosystems, of this strain, due mainly to the high plasticity to different environmental conditions. Among the potential limiting factors, a strong dependence on the trophic input was demonstrated, influencing growth rate, and a potential long term effects of water pollution may be present, especially when populations remains small as in the studied cases.