Multiple origins of stone loach,Barbatula barbatula (Teleostei: Nemacheilidae), in Sweden based on mitochondrial DNA

Stone loach, Barbatula barbatula, occurs in scattered localities in Sweden. Some of the populations have usually been considered as feral descendants of escaped 18th Century pond stock, but historical documentation is inconclusive. Using the mitochondrial COI gene as a marker, we analyzed specimens from seven Swedish localities. One of the middle Swedish localities, in Stockholm, belongs to a haplotype found also in Poland and Lithuania. Two other samples, from near Nyköping and Lake Hjälmaren, belong to a haplotype found in northeastern Europe (Finland, Estonia, Latvia, Volga basin in Russia). Those two Swedish populations are probably descendants from at least two introductions, probably for pond rearing for human consumption. Samples from Skåne and Halland in southern Sweden belong to the haplotype found in Denmark, northern Germany and Poland; and whereas it remains possible that they also represent feral populations, they may be naturally occurring, having reached Sweden during the Ancylus period, about 8,000–10,000 years ago. A recently discovered population from the central South Swedish Highlands belongs to a mainly southeastern European haplotype. It probably represents a release of imported aquarium specimens or live bait carried by sport fishing tourists.