Fish trypanosomes: Their position in kinetoplastid phylogeny and variability as determined from 12S rRNA kinetoplast sequences

Fish trypanosomes have traditionally been classified according to the host species from which they were isolated, each isolate being regarded as a dis tinct species. To test the soundness of this practice, the genetic variabil ities of the kinetoplast 12S rRNA-encoding genes of different fish trypanos omes isolates were compared. The DNAs were extracted from trypanosomes clon ed from blood samples of 15 donors representing ten different fish species in four orders from waters of three major river systems of Central and Nort hern Europe. Comparison with other trypanosomatid sequences revealed that t he fish trypanosomes form a monophyletic group with Trypanosoma brucei as a sister group. Pairwise comparisons of genetic distances yielded a wide ran ge of continuous variation with no indication of any discontinuities attrib utable to barriers to gene flow. The genetic distances did not correlate wi th either the identity of the host species or geography. The host specifici ty of fish trypanosomes appears to be limited.