Alien fish species in the Balkans

What is it about?

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 naturalised in inland waters. Since the Balkans are one of the world’s 35 biodiversity hotspots, 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, vary 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 paper 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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Why is it important?

The current study has shown that a large proportion of alien species in the Balkans are widespread and are fully invasive species by the criteria of Blackburn et al. (2011). Major corridors for their spread are the transboundary rivers and lakes, such as Ohrid-Drin-Skadar river system draining a number of countries in the Balkans, or the Danube River draining a large section of Central and Eastern Europe. In the Balkans, most major rivers and lakes are transboundary, creating conflicts of interest since water resources are unevenly distributed among the countries. There is a strong need for coordination in river managment issues, such as pollution control, hydroelectric energy production, and the control of alien fishes. The current study has also revealed the true extent of the gaps in the knowledge on the current state, distribution and impacts of many alien species in the Balkans. These gaps should be targeted through coordinated research that could assist effective conservation efforts.

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