Mitochondrial-Dna Nucleotide-Sequence Variation in Atlantic Salmon (Salmo-Salar), Brown Trout (Salmo-Trutta), Rainbow-Trout (Oncorhynchus-Mykiss) and Brook Trout (Salvelinus-Fontinalis) From Tasmania, Australia

The unique properties of the mitochondrial genome were used to investigate features of the population dynamics and origins of the species. No restriction site variation was found among samples of Tasmanian Atlantic salmon or among rainbow trout mitochondrial genomes. This lack of mtDNA diversity in Atlantic salmon may have been caused by a transitory, but significant, decrease in brood stock numbers in the hatchery from which the Tasmanian population was derived. Rainbow trout may have low levels of mtDNA diversity due to repeated cycles of hatchery and wild propagation in New Zealand, mainland Australia and in Tasmania. A freshwater and a sea-running population of brown trout were found to have identical mitochondrial genomes, despite the introduction to Tasmania of numerous strains of northern hemisphere fish, each of which could logically be assumed to carry its own characteristic mtDNA. In combination with historical evidence, it is suggested that only the first introduction of a 'few hundred' brown trout in 1864 produced acclimated populations and that the small number of maternal lines in this founding population accounts for the observed lack of mtDNA diversity. Two brook trout haplotypes were found among a sample of only 18 Tasmanian fish, suggesting that the founding stock of brook trout which was introduced to Tasmania in 1962 possessed considerable mtDNA diversity despite its supposed hatchery origin