Role of the introduced freshwater fishes in Bulgaria: economical benefits and ecological consequences.
In Bulgaria fresh water basins over 20 exotic fish species have been introduced. Most of the introductions were made in the 70's. In the last five years the share of these species in the Bulgarian aquaculture continuously increases. The amount of aquaculture production from non-indigenous species is about 70% from the all production for 2004. Some introductions undoubtedly have significant economical advantage. In the rest of the cases the aims was to increase biodiversity, recreational activities or biomanipulation in water reservoirs. But these positive results are accompanied by some negative consequences such as unintentional introduction of several weed species as Pseudorasbora parva and pumpkinseed (Lepomis gibbosus). In many cases, these species have formed dense populations and it is blamed for the strong food competition with other species. Another undesirable consequence is the introduction of different parasites and diseases. In conclusion, several basic measures are outlined in order to prevent the negative ecological consequences from fish introduction.