Rivers in the karst region represent very specific and today particularly endangered water phenomena. The reason for this is the limestone rocks of the karst relief in which any water that reaches the surface is very quickly filtered underground. The ichthyofauna with the highest degree of endangerment and endemism is most often found in intermittent watercourses such as the Čikola River and its only tributary, the Vrba. In such hydrologically most dynamic systems, processes such as floods (during the autumn and winter period) and droughts (summer period) affect the connectivity or disconnection of watercourses, which results in very large fluctuations in the availability of nutrients and the diversity of living things. Isolated small water bodies (pools) that remain after a drought are used by fish as refugiums, and since this is a seasonal phenomenon, many of them have developed adaptations to survive the poor conditions in them, which we recorded as part of last year’s sectional project “Invasive Ichthyofauna of the Čikola River”.
The diversity of freshwater fish species in Croatia is exceptional, and according to the 2019 freshwater fish list (Ćaleta et al. 2019), the Adriatic basin in the Republic of Croatia is inhabited by 80 species of ray-finned fish. As many as 38 of them are endemic to Croatia and the Adriatic basin, of which three are present in the Čikola River. Čikola and Vrba are areas within the NATURA 2000 ecological network (Regulation on the ecological network, “Official Gazette”, number 124/13) HR2000919 Čikola, HR2001266 Vrba conservation area important for species and habitat types (POVS). The Turkish chub (Telestes turskyi) and the Dalmatian scaup (Phoxinellus dalmaticus) are considered critically endangered species and stenoendemics of Čikola (which means that on a global scale they only inhabit the specified, isolated and limited area), while the scaup (Aulopyge huegelii) has the status of an endangered species and inhabits the wider area of the Cetina River and the Livanjsko polje.
The project “Invasive ichthyofauna of the Čikola River” in 2023, an inventory of the ichthyofauna of the Čikola River was carried out on three occasions with an emphasis on invasive species, except for the canyon part (half of the area) and the Vrba tributary. The goal of this
of the project was to investigate in more detail the distribution of endemic fish species in the canyon section Chikole in refugia during drought and in the course of the Vrba river during high water levels. Project represented a kind of continuation of the previously carried out inventory of invasive species of the Čikola River, and in order to complete the collected data, localities that were not covered by past field trips such as the river Vrba and additional localities in Petrovo polje.
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