Brown trout of German origin were introduced into Patagonian National Parks in 1905, where they acclimatized and underwent population expansion endangering populations of native species like Galaxiidae. Spawning adults of two populations were sampled in 2004. Their age, length-at-age and migratory behaviour were assessed from scale samples, as well as their variation at the coding LDH-C1* and eight non coding microsatellite loci. Betweenpopulation differentiation for life history (spawning time, migratory behaviour, length and weight at age) and reduced genetic variation were revealed. Based on genetic variation, effective population size smaller than 50 individuals has been estimated for the founder stock, and its German origin has been genetically traced. Flexibility in migratory behaviour and spawning time were identified as key factors conferring competitive advantage on those brown trout populations.
Three salmonid species introduced in Patagonian national parks in Argentine have experienced different degrees of expansion. Atlantic salmon Salmo salar is restricted to a few river‐lake systems and its populations have been declining over recent years. Both rainbow Oncorhynchus mykiss and brown trout Salmo trutta populations have expanded from their introduction sites and now occupy a wide range of freshwater ecosystems. Genetic variation at the same neutral markers (microsatellite loci) was examined for different populations of the three species acclimatized to the same areas, and compared with that of native populations. Founder effects denoted as reduced variability and great differentiation with respect to the native populations were detected. Significant reduction in variability has not been an obstacle for successful adaptation of rainbow and brown trout, indicating that genetic variability per se cannot be claimed as the reason for their different outcomes in the new habitats.
Salmonids are fish from the Northern Hemisphere which have been introduced and acclimated to many regions in the Southern Hemisphere for commercial (aquaculture) and recreational (sport fishing) purposes. In some cases a species like brown trout Salmo trutta rapidly spread across the host ecosystem and became invasive, threatening local fauna, and even outcompeting other exotic fish. We have analyzed life-history traits in combination with genetic variation of Atlantic salmon and brown trout adapted to the lake systems of the Argentinean Patagonia (South America). We have identified two main characteristics that conferred invasive capacity to those exotic species: undomesticated status and lifelong growth. Stocks originated from wild populations adapted better than long-term domestic lineages, and their geographic origin seems to be less important for adaptation to exotic environments. We propose that considering these characteristics in future planning of commercial aquaculture projects by selecting non-invasive lineages will minimise the impact of accidental escapes.
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