Small subunit ribosomal RNA and mitochondrial cytochrome c oxidase subunit 1 gene sequences of 21 strains of the parasitic scuticociliate Miamiensis avidus (Ciliophora, Scuticociliatia)

The scuticociliate Miamiensis avidus is a histophagous parasite that causes high mortality in cultured marine fishes. Small subunit ribosomal RNA (SSU rRNA) and mitochondrial cytochrome c oxidase subunit 1 ( cox 1) genes were analyzed for 21 strains of M. avidus isolated from diseased olive flounder ( Paralichthys olivaceus ), ridged-eye flounder ( Pleuronichthys cornutus ), and spotted knifejaw ( Oplegnathus fasciatus ) in Korea and Japan (collected in 2003–2007). Analysis of SSU rRNA gene sequences (1,759 bp) indicates they are very conserved with less than 0.17% (3 nucleotides) differences suggesting that SSU rRNA are useful to identify M. avidus ; however, the cox 1 gene (900 bp) has higher variations with intraspecific divergences up to 5.67% (51 nucleotides). A distance tree of cox 1 gene sequences based on a neighbor-joining analysis can separate 21 strains into five cox 1 types (two heterogeneous clusters and three individual branches). The cox 1-type matches with serotype of strains but do not reflect geographical origins, host species, or pathogenicity.