Supportive breeding program of Marble trout (Salmo marmoratus) in the Province of Bolzano - Italy

The marble trout populations of the Northern Adriatic basin are threatened by human mediated hybridisation with exotic brown trout. Therefore, conservation measures are urgently needed to counteract further hybridization of this endemic species. The novel supportive breeding program described in this poster, applied within the Province of Bolzano since 2016, aims to conserve the genetic integrity of marble trout, while avoiding both domestication effects and the reduction of effective population size. Local wild marble trout spawners, selected by a genetic screening of each single individual, constitute the basis of the program. To minimize a potential reduction of effective population size induced by supportive breeding, full or partial factorial crossing is conducted. The main part of fertilized eggs is stocked back into the rivers of origin. However, currently it is also a necessary measure to hatch a fraction of the descendants of each trout family under semi-natural conditions. This is done in order to increase the number of available parental fish, and further to be able to provide adequate quantities of fertilised eggs, used for stocking in artificial nests of all river stretches. The genetic screening of wild marble trout (N=578 in 2018) showed a significant hybridization for 80 percent of the phenotypically preselected spawners. The elevated degree of genetic introgression is hampering the here described supportive breeding programs, since it will be more and more difficult to maintain sufficient number of breeders and, in general, pose a serious threat for the conservation of the species within the area of interest