The Alien Peipsi Whitefish Coregonus maraenoides Polyakov, 1874 (Actinopterygii: Salmoniformes) in Iskar Reservoir, Danube River basin, Bulgaria

摘要

In the 1960-1970s, three coregonid fishes (Coregonus albula, Coregonus maraenoides and Coregonus peled) were imported from the former Soviet Union and introduced to some reservoirs in Bulgaria. Irregular import, hatching in local fish-farms and stocking continued until the 1990s. The aim of our study was to examine the occurrence of the alien coregonid species in one of the stocked reservoirs. Iskar Reservoir. and to identify the species recorded based on their morphology. A total of 54 coregonid specimens were collected at five stations in the period from October to March in 2015 and 2016. According to the studied morphometric and meristic data, all the coregonid specimens collected were identified as the Peipsi whitefish, Coregonus maraenoides. The morphology of C. maraenoides from Iskar Reservoir revealed some differences from the native population (Peipus Lake, Estonia and Russia), being most likely a result of adaptation of this species to the local environmental conditions or related to the brood stock management in the fish farms. Our results showed that C. maraenoides has successfully established in the reservoir. The existence of self-sustaining population has been supported by the following: a long period from the last stocking of C. maraenoides to the reservoir up to our study (>15 years); presence of specimens of different size classes in the catches; and presence of sexually mature female and male specimens.