The geographical distributions of mitochondrial DNA (mtDNA) haplo-types in non-indigenous populations of a freshwater goby,
Tridentiger brevispinis, were investigated. Although 26 mtDNA haplotypes were obtained from 168 individuals (including a closely-related species,
T. obscurus) representing 36 indigenous populations, only two haplotypes (I-Al and III-B1) were found in 59 individuals of
T.brevispinis from 12 non-indigenous populations. Many of the latter had the I-Al haplotype, thepopulations being located near indigenous populations having the same haplotype. A non-indigenous population in Lake Biwa had the III-B1 haplotype, the lake being close to the natural distribution area of that haplo-type. Thus, the non-indigenous populations of
T. brevispinis may have become es-tablished following artificial transplantations from nearby populations. The III-B 1 haplotype, however, was also scattered throughout geographically-distant, non-in-digenous populations, its dispersal possibly having been a consequence of trans-plantation of Ayu (
Plecoglossus altivelis), from Lake Biwa, accompanied by
T. brevispinis. However, the primary cause of the expansion of non-indigenous goby populations retains unclear.
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