Morphological and molecular characterization of Posthodiplostomum sp. (Digenea: Diplostomidae) metacercaria in the muscles of snakeheads (Channa punctata) from Manipur, India

The spotted snakehead, Channa punctata Bloch, 1793, is a locally important fish species commonly consumed by the natives in the state of Manipur, Northeast India. The fish host C. punctata from Lamphel area revealed a diplostomid metacercarial infection. Morphologically, the recovered metacercaria was identified as a species of Posthodiplostomum Dubois, 1936. Molecular characterization using the ribosomal RNA genes (rDNA 18S, ITS2 and 28S regions) and the mitochondrial CO1 region supplements the identification. Molecular analysis revealed the metacercaria to be closely related to Posthodiplostomum sp. Japan isolate, with sequence similarity variation from 97.5–99.7 % while considering for the three rDNA markers. The secondary structure of the ITS2 region further corroborated these results; the typical four-helix model, when compared to the taxon from Japan, showed differences only in twelve bases (with seven transitions and five transversions). In phylogenetic analysis also, the metacercaria claded with the genus Posthodiplostomum, coming closer to the Japanese isolate, thus supplementing the morphological identification of the metacercaria.