In recent years, policy-makers have sought the development of appropriate tools to prevent and manage introductions of invasive species. However, these tools are not well suited for introductions of non-target species that are unknowingly released alongside intentionally-introduced species. The most compelling example of such invasion is arguably the topmouth gudgeon Pseudorasbora parva, a small cyprinid species originating from East Asia. A combination of sociological, economical and biological factors has fuelled their rapid invasion since the 1960s; 32 countries (from Central Asia to North Africa) have been invaded in less than 50 years. Based on a combination of monitoring surveys (2535 populations sampled) and literature reviews, this paper aims to quantify and characterise important invasion parameters, such as pathways of introduction, time between introduction and detection, lag phase and plasticity of life history traits. Every decade, five new countries have reported

The marble trout (Salmo marmoratus) is an endangered species in Slovenia (and in Italy, Croatia and Albania) because of hybridization resulting from intensive stocking. Eleven populations of trout from the Soca river basin (Slovenia) were analysed using 31 presumptive enzyme loci. Three European control samples representing the main European genotypes of brown trout were also analysed. This analysis con®rmed the existence of extensive hybridization in the main river, resulting in an equal mixture of alleles belonging to marble trout, and Danubian and Atlantic brown trout (Salmo trutta). Despite the high level of introgression observed in the main Soca River, nearly pure populations of marble trout were found in the headwaters of ®ve tributaries. The ®ve stations with pure marble trout will be the basis of a rehabilitation programme. Hardy±Weinberg and linkage disequilibria were observed and hypotheses are discussed to explain this. A scenario for the colonization of the Adriatic region is proposed.

The Fish Invasiveness Screening Kit (FISK) version 2 was used to assess the invasiveness potential of 40 introduced and translocated freshwater fish species to Croatia and Slovenia. Based on a priori classification of invasiveness, receiver operating characteristic analysis of FISK scores from two independent assessors resulted in a statistically significant calibration threshold of 11.75. This indicated that FISK was able to discriminate reliably between non‐native species likely to pose a high risk of being invasive and those likely to pose a medium or low risk of invasiveness. Seven species were categorised as ‘medium risk’ and the other 33 as ‘high risk’, whereas no species was categorised as ‘low risk’. The two highest scoring species were European catfish Silurus glanis and North African catfish Clarias gariepinus. Mean scores for all species classified a priori as invasive were ranked as ‘high risk’ sensu lato and fell into the ‘moderately high risk’ subcategory. FISK proved to be a valid tool for assessing the risks posed by non‐native fishes in Croatia and Slovenia. For this reason, it can be adopted as a reliable tool for the prevention of new translocations or introductions of potentially invasive species in the risk assessment area, as well as to assist in decisions regarding future management (i.e. monitoring, control and eradication) and conservation strategies.

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