Assessment of the stocked or wild origin of anadromous brown trout (Salmo trutta L.) in a Danish river system, using mitochondrial DNA RFLP analysis


  • Michael M. Hansen is the staff population geneticist at the Inland Fiiheries Laboratory which is directed by Gorm Rasmussen. The Inland Fsheries Laboratory is, among other things, responsible for the management and conservation of freshwater fishes in Denmark. This paper represents a part of the results of MMH's PhD project which concerned the impact of stocking activity on the nalural genetic populaHon structure of brown trout. Rosaleen A. Hynes is Experimental Officer in charge of the fish genetics laboratory at Queen's University, Belfast. Volker Loeschcke is Associate Frofessorat theuniversityof Aarhusand has forseveral yearsbeen engaged in genetic and ecological aspects of cunserva tion


Declines in the number of anadromous brown trout in the Karup River in Denmark, due to environmental degradation, led to the stocking of large numbers of hatchery trout during the 1980s. This practice was gradually replaced by stocking with the offspring of electrofished local trout The genetic contribution of the hatchery fish to the current population of anadromous trout in the river was estimated by restriction fragment length polymorphism analysis of mitochondrial DNA, using seven restriction endonucleases. Fish from the hatchery strain as well as from five locations in the river system, and from a further unstocked river were screened. Eight haplotypes were observed. The distribution and frequencies of the observed haplotypes revealed little genetic differentiation among stocked populations. The hatchery strain differed significantly from the stocked populations. One haplotype which was found at a high frequency in the hatchery strain was almost absent from the stocked populations. This suggests that the genetic contribution of the hatchery trout to the current population is much less than would be expected from the number of stocked fish. The possible reasons for the failure of the hatchery trout to contribute to the gene pool, and also the implications for conservation biology, are discussed.