The Freshwater Fish Invasiveness Screening Kit (FISK) v2 and Aquatic Species Invasiveness Screening Kit (AS‐ISK) risk identification screening tools were used to assess the invasiveness potential of 24 non‐native (NNS) freshwater fish species in the River Neretva catchment (Bosnia and Herzegovina and Croatia), a risk assessment (RA) area that is an important Mediterranean hotspot for fish endemism. The two assessors assigned similar scores for the invasiveness potential of the NN fishes, and both screening tools successfully distinguished invasive from non‐invasive species. Mean calibrated threshold scores were 10.25 for FISK and 10.00 for AS‐ISK, with the latter increasing to 12.62 when questions that assess the likely impact of predicted future climate conditions on the RA were taken into consideration. These relatively low threshold values are characteristic of areas with an elevated number of translocated species and suggest that NN fishes pose a considerable threat to native species and ecosystems. FISK ranked 50.0–62.6% of the species as being of ‘high risk’ compared with 58.4–59.3% using AS‐ISK. The highest scores (‘very high risk’) were attributed to gibel carp Carassius gibelio (Bloch, 1782) and pikeperch Sander lucioperca (Linnaeus, 1758). The generic screening tool for aquatic species (AS‐ISK) provided similar risk rankings to its predecessor, FISK, as regards invasiveness potential. For this reason, it is likely to be an effective tool for evaluating the potential invasion risk of NNS freshwater fishes for other RA areas in the Balkans. Copyright © 2017 John Wiley & Sons, Ltd.

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Biological invasions are a major driver of global environmental change as invasive non‐native species can exert severe environmental impacts on invaded ecosystems. Estuaries are especially vulnerable to biological invasions, which in highly urbanised areas are further facilitated by introduction pathways linked to commercial activities. This study provides a risk screening of non‐native invasive species for the highly urbanised River Neretva Estuary (Eastern Adriatic Sea: Croatia and Bosnia–Herzegovina). In total, 12 species of non‐native aquatic organisms were identified and screened for their invasiveness with the Aquatic Species Invasiveness Screening Kit. Of these species, eight were classified as carrying a high risk of invasiveness under current climate conditions and nine under future climate conditions. Amongst the high‐risk species, blue crab Callinectes sapidus has already caused impacts in the risk assessment area, where it also represents an important economic resource. The “horizon” species Pacific oyster Crassostrea gigas and Manila clam Ruditapes philippinarum also carried a high risk of invasiveness, which for the latter species applied under predicted global warming. The present findings will contribute towards preventative management and control measures for the conservation of the natural ecosystem of the River Neretva Estuary whilst accounting for aquatic farming demands.

Salmonids are an extensively hatchery-reared group of fishes that have been introduced worldwide mainly for their high commercial and recreational value. The Balkan Peninsula (south-eastern Europe) is characterised by an outstanding salmonid diversity that has become threatened by the introduction of non-native salmonids whose potential risk of invasiveness in the region remains unknown and especially so under predicted climate change conditions. In this study, 13 extant and four horizon non-native salmonid species were screened for their risk of invasiveness in the Danube and Adriatic basins of four Balkan countries. Overall, six (35%) of the screened species were ranked as carrying a high risk of invasiveness under current climate conditions, whereas under predicted conditions of global warming, this number decreased to three (17%). Under current climate conditions, the very high risk (‘top invasive’) species were rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta (sensu stricto), whereas under predicted climate change, this was true only of O. mykiss. A high risk was also attributed to horizon vendace Coregonus albula and lake charr Salvelinus namaycush, and to extant Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis, whose risk of invasiveness, except for S. fontinalis, decreased to medium. For the other eleven medium-risk species, the risk score decreased under predicted climate change, but still remained medium. The outcomes of this study reveal that global warming will influence salmonids and that only species with wider temperature tolerance, such as O. mykiss will likely prevail. It is anticipated that the present results may contribute to the implementation of appropriate management plans to prevent the introduction and translocation of non-native salmonids across the Balkan Peninsula. Additionally, adequate measures should be developed for aquaculture facilities to prevent escapees of non-native salmonids with a high risk of invasiveness, especially into recipient areas of high conservation value.