Sequence conservation in the internal transcribed spacers and 5.8S ribosomal RNA of parasitic scuticociliates Miamiensis avidus (Ciliophora, Scuticociliatia)

Abstract

The scuticociliate Miamiensis avidus is a histophagous parasite that causes high mortality in cultured marine fishes, with clinical signs of severe ulcers and hemorrhages in the skeletal muscle. The internal transcribed spacer (ITS) region, which is widely used in taxonomy and molecular phylogeny because of a high degree of variation, was compared for 21 cloned strains of M. avidus (Ciliophora, Scuticociliatia). These strains were isolated from olive flounder Paralichthys olivaceus, ridged-eye flounder Pleuronichthys cornutus and spotted knifejaw Oplegnathus fasciatus in Korea and Japan. The ITS1 (140 bp), ITS2 (236 bp) and 5.8S (119 bp) regions from 21 strains were identical, indicating that these regions are highly conserved in M. avidus. Phylogenic analysis of ITS2 shows that the ciliate should be included in the Philasterida with a close relationship to Pseudocohnilembus hargisi. This study exhibits the first detailed analysis of the ITS1, 5.8 S and ITS2 rRNA regions of M. avidus.