Biological invasions and introgressive hybridization are major drivers for the decline of native freshwater fish. However, the magnitude of the problem across a native species range, the mechanisms shaping introgression as well as invader's dispersal and the relative role of biological invasions in the light of multiple environmental stressors are rarely described. Here, we report extensive (N = 665) mtDNA sequence and (N = 692) microsatellite genotypic data of 32 Northern Adriatic sites aimed to unravel the invasion of the European Barbus barbus in Italy and the hybridization and decline of the endemic B. plebejus. We highlight an exceptionally fast breakthrough of B. barbus within the Po River basin, leading to widespread introgressive hybridization with the endemic B. plebejus within few generations. In contrast, adjacent drainage systems are still unaffected from B. barbus invasion. We show that barriers to migration are inefficient to halt the invasion process and that propagule pressure, and not environmental quality, is the major driver responsible for B. barbus success. Both introgressive hybridization and invader's dispersal are facilitated by ongoing fisheries management practices. Therefore, immediate changes in fisheries management (i.e. stocking and translocation measures) and a detailed conservation plan, focussed on remnant purebred B. plebejus populations, are urgently needed.

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The marble trout, a lineage of the Salmo trutta complex, is endemic to the Southern Alpine region. Although it is endangered throughout its entire distribution range, population genetic data were lacking for the central area, including the upper Etsch/Adige River system (South Tyrol, Northern Italy). A total of 672 Salmo trutta specimens, comprising phenotypic marble trout and phenotypic brown trout, from 20 sampling sites throughout South Tyrol were analysed by sequencing the complete mitochondrial DNA control region. Thirteen distinct haplotypes were identified, which clustered within three major genetic lineages: the Marmoratus (MA), the Atlantic (AT) and the Danubian (DA) lineage. 41.7% of the investigated individuals carried haplotypes of the MA lineage, 47.9% of the AT lineage and 10.4% of the DA lineage. It is noticeable that AT haplotypes were present at all sampling sites and no ''pure'' marble trout population with exclusively MA haplotypes was found. This points to a considerable impact of stocking with allochthonous brown trout, given that there is no evidence for natural colonisation by individuals of the AT lineage. However, our data indicate, for at least four localities, a limited gene flow between the native marble trout and hatchery-reared strains. Future conservation and rehabilitation measures will thus have to concentrate on the identification of remnant pure marble trout individuals from such mixed populations.

The management of recreational fisheries benefits from good collaboration between scientists, managers and recreational fishers. However, the level of collaboration largely depends on the levels of effective communication among the different stakeholders. This paper presents the views of scientists, managers and fishers concerning the quality of communication in eleven case studies of recreational fisheries. Case studies were synthesised and common reasons why communication did not always flow as intended were identified. The prevalent barriers to good communication, and therefore collaboration included a lack of rigorous scientific information transfer from scientists to fishers and managers, a fear from fishers that management actions will limit fishing opportunities, pre‐existing antagonism between commercial and recreational fisheries, and fishers' suspicion of science. Overcoming these issues is paramount to improve collaboration and participatory processes that help lead to robust, well‐accepted management actions.

Phylogeographic information on European grayling, Thymallus thymallus, is still fragmentary for the Northern Adriatic basin. In this article, we provide complete mitochondrial DNA control region sequence data of 456 grayling specimens from 21 sampling sites across distinct river drainages. Thirty-seven haplotypes were resolved and clustered into Danubian, Atlantic and Adriatic lineages. The latter clade, composed of 16 new haplotypes, was identified in 12 out of 17 Adriatic sampling sites and reached frequencies of 0.97 within single water courses of the Adige and the Po drainages. However, native Adriatic haplotypes were accompanied by Danubian and/or Atlantic variants in all cases. A positive correlation between hatchery haplotype frequency and annual stocking input pointed to a direct effect of stocking intensity on the genetic architecture of wild populations, although natural trans-basin colonisation may have additionally complicated the situation. However, both the extent and patterns of introgression between native and foreign strains, as well as microgeographic population structure within the Adriatic lineage will be clarified by future molecular surveys, based on nuclear genetic markers. Until then, conservation management must include an immediate cessation of stocking of commercial grayling stocks, as well as the prohibition of grayling translocation, even at the intra-drainage level.

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Phylogeny of Northern Adriatic Salmo trutta is still not resolved, leading to taxonomic controversies and hindering reasonable conservation and fisheries management. We report on the genetic screening of 467 brown trout from 25 sites within Adige, Brenta and Po River drainage basins (Italy). Our main aim was to identify native (Adriatic) brown trout within the central part of the Northern Adriatic area. D-loop lineage screening evidenced a predominance of the Atlantic clade with a frequency of 0.87, followed by the Marmoratus clade with 0.11, and, finally, the Adriatic clade with a frequency of 0.02. The Adriatic clade was found exclusively in specimens from Pianetti River and was represented by haplotype Adcs1. However, microsatellite-based analysis of population structure within Pianetti River specimens failed to identify Adriatic brown trout, but pointed to a nuclear genomic replacement of the former by Atlantic strains. In conjunction with earlier phylogenetic studies, our results contrast with a present-day widespread distribution scenario of Adriatic brown trout within the Northern Adriatic region. From a conservation viewpoint, the punctiform occurrence of Adriatic haplotypes, their ambiguous provenance, and, finally, the presumable genomic replacement at the nuclear genetic level, might hinder reasonable conservation actions and call for revised fisheries management guidelines

Marble trout, endemic to the Adriatic drainage basin, is severely threatened by hybridisation with nonnative brown trout. In the present study, we analysed 12 microsatellite DNA loci to assess genetic population structure and differentiation between sympatric phenotypic marble and brown trout at nine sampling sites in the upper Etsch/Adige River system. F ST and AMOVA analyses revealed significant genetic differentiation between marble and brown trout samples. Thus, admixture between brown and marble trout appears to be incomplete. However, factorial correspondence analysis depicted marble trout, Atlantic brown trout and intermediate genotypes. Bayesian-based individual assignment tests identified indigenous marble trout at five sampling sites. In four other samples no 'pure' marble trout were detected. Bidirectional, first-generation hybridisation, involving both sexes of both parental species was observed. In locations where 'pure' marble trout still exist, post-F1 hybridisation appears to be directed towards brown trout. This has likely slowed the rate of hybridisation between the two trout species and the decline of relic marble trout populations. Based on these results, restoration management actions are proposed, such as the abandonment of brown trout stocking activities, sharper angling policies, establishment of indigenous marble trout breeding strains and the elaboration of a conservation priority list.