Phylogenetic position of the freshwater fish trypanosome, Trypanosoma ophiocephali (Kinetoplastida) inferred from the complete small subunit ribosomal RNA gene sequence.

The complete small subunit rRNA (SSrRNA) gene sequence (2,142 nucleotides) of the freshwater fish trypanosome Trypanosoma ophiocephali Chen (1964) was determined. The phylogenetic analysis deduced using neighbor-joining, maximum parsimony, and Bayesian methods demonstrated the existence of an "aquatic clade". T. ophiocephali was revealed to be a member of the freshwater fish trypanosomes and form the sister species with Trypanosoma siniperca and Trypanosoma sp. Carpio with high bootstrap values (98% MP, 100% NJ, 100% Bay). The high similarity of SSrRNA gene sequences and morphometric characters showed that T. ophiocephali, T. siniperca and T. sp. Carpio probably were the same species. The phylogenetic trees further suggested that Chinese freshwater fish trypanosome might be paraphyletic, and fish trypanosomes should have low host specificity.