Fish introductions, particularly in areas of high biological diversity and endemism, represent a major threat for biodiversity. In the Balkan Peninsula, 60 fish species have been introduced to date, of which 36 have become naturalized in inland waters. Since the Balkans are one of the world's 35 biodiversity hot spots, this large presence of alien fish species poses a serious threat for the stability of freshwater ecosystems and the survival of the native ichthyofauna and of aquatic biodiversity in general. The motivation for the introductions, and the historical timeline, varies among the Balkan states. Despite recent attempts to implement and align legislation aimed at preventing the introduction of potentially invasive species, and the implementation of rigorous controls of introductions and increased protection of open waters, the majority of current introductions remain intentional, primarily via aquaculture. This review article provides a historical overview of freshwater fish introductions, the motivation behind them and the current distribution of alien freshwater fishes in the Balkans. The ecological implications and future perspectives concerning alien fish species in the region are also discussed.

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A high level of freshwater fish endemism in the Balkans Region emphasizes the need for non-native species risk assessments to inform management and control measures, with pre-screening tools, such as the Fish Invasiveness Screening Kit (FISK) providing a useful first step. Applied to 43 non-native and translocated freshwater fishes in four Balkan countries, FISK reliably discriminated between invasive and non-invasive species, with a calibration threshold value of 9.5 distinguishing between species of medium and high risk sensu lato of becoming invasive. Twelve of the 43 species were assessed by scientists from two or more Balkan countries, and the remaining 31 species by a single assessor. Using the 9.5 threshold, three species were classed as low risk, 10 as medium risk, and 30 as high risk, with the latter category comprised of 26 moderately high risk, three high risk, and one very high risk species. Confidence levels in the assessments were relatively constant for all species, indicating concordance amongst assessors.

The ontogenetic development of the chondrocranium of Ohrid trout Salmo letnica was studied from hatching until 92 days post-hatching (dph). Most of the samples were in toto trypsin cleared and stained, some specimens were used for serial histological sectioning. The serial histological sections of fish specimens at the age of 92 dph were used for a graphical reconstruction of the cartilaginous neurocranium. A chronological evaluation of the formation of the cartilaginous skull in the early development of S. letnica was performed. In order to investigate to what degree the ontogeny of the Ohrid trout is unique, the results were compared with data of the development of other salmonids, as well as some non-salmonid teleosts. The development of the cartilaginous structures of the Ohrid trout was found to be similar to that of other salmonids. Most of the cartilage structures of the neurocranium and the viscerocranium are present at the moment of hatching of this species. A fully developed chondrocranium was observed at the age of 92 dph, when the first signs of cartilage resorption could also be observed.

Electronic decision-support tools are becoming an essential component of government strategies to tackle non-native species invasions. This study describes the development and application of a multilingual electronic decision-support tool for screening terrestrial animals under current and future climate conditions: the Terrestrial Animal Species Invasiveness Screening Kit (TAS-ISK). As an adaptation of the widely employed Aquatic Species Invasiveness Screening Kit (AS-ISK), the TAS-ISK question template inherits from the original Weed Risk Assessment (WRA) and related WRA-type toolkits and complies with the ‘minimum requirements’ for use with the recent European Regulation on invasive alien species of concern. The TAS-ISK consists of 49 basic questions on the species’ biogeographical/historical traits and its biological/ecological interactions, and of 6 additional questions to predict how climate change is likely to influence the risks of introduction, establishment, dispersal and impact of the screened species. Following a description of the main features of this decision-support tool as a turnkey software application and of its graphical user interface with support for 32 languages, sample screenings are provided in different risk assessment areas for one representative species of each of the main taxonomic groups of terrestrial animals supported by the toolkit: mammals, birds, reptiles, amphibians, annelids, insects, molluscs, nematodes, and platyhelminths. The highest-scoring species were the red earthworm Lumbricus rubellus for the Aegean region of Turkey and the New Zealand flatworm Arthurdendyus triangulatus for Croatia. It is anticipated that adoption of this toolkit will mirror that of the worldwide employed AS-ISK, hence allowing to share information and inform decisions for the prevention of entry and/or dispersal of (high-risk) non-native terrestrial animal species – a crucial step to implement early-stage control and eradication measures as part of rapid-response strategies to counteract biological invasions.

Carabid fauna is not sufficiently explored in Central and Western Balkan areas, especially in mountain ecosystems with unique biodiversity which is a result of specific environmental factors and geologic history. Furthermore, distribution of species and adaptation to varying environmental parameters change along the altitudinal gradients. All this highlights the need for biodiversity and ecological studies in order to assess the state of the mountain ecosystems and conservation significance. Carabids as good bioindicator group can be used as a tool for monitoring those changes. The aim of this study was to analyse the differences of body size distribution and mean individual biomass (MIB) of ground beetle assemblages as a response of changing conditions and vegetation types along an altitudinal gradient on Belasitsa Mountain in south Macedonia. Both parameters significantly decreased with increasing altitude and were consequently associated with the vegetation type. Larger bodied individuals and higher values of MIB were recorded in the white oak and oriental hornbeam forest stands with the values decreasing in sessile oak forests towards submontane and montane beech forest stands. This research yielded first list of carabid species inhabiting Belasitsa Mountain with insight of carabid body length and biomass distribution along altitudinal gradient.

Abstract:In the present study, we analysed spatial and temporal heterogeneity of the limnological characteristics to provide more detailed information about the processes taking place within Mantovo Reservoir (Republic of Macedonia). The relationship between principal macroinvertebrate species and environmental variables was analysed in order to explore factors that dominantly affect community distribution pattern. Unlike the most reservoirs, strong longitudinal gradient for suspended organic matter and nutrients (total phosphorous, nitrates and nitrites) along the reservoir doesn't exist. However, the process of thermal stratification has a strong influence on the metabolism and structure of the Mantovo ecosystem, which can be demonstrated by the vertical and longitudinal distribution of dissolved oxygen (DO), CO2, pH and metals concentrations. Canonical Correspondence Analysis (CCA) indicated that the main factors controlling spatial distribution of Limnodrilus hoffmeisteri and Chironomus plumosus group were temperature, dissolved oxygen and manganese, including sulphates for C. plumous group. Chaoborus crystallinus showed opposite distribution pattern. Cladotanytarsus mancus group was strongly associated with shallower part (littoral and sublittoral) of Mantovo Reservoir characterized by favourable oxygen condition. None of the environmental variables included in CCA showed any relationship with density of Procladius sp.