Morphological and molecular characterization of a novel Myxobolus species from the gastrointestinal tract of brown trout (Salmo trutta) in Spain.

The genus Myxobolus Bütschli, 1882 is the largest group within the class Myxosporea and includes 905 nominal species, 18 of which have been found to infect fish belonging to the family Salmonidae. In the present study, microscopic analysis enabled detection of myxospores in 43 of 613 (7.0%) gastrointestinal tracts from brown trout (Salmo trutta) captured in several rivers in the northwest of the Iberian Peninsula. Measurement of the whole myxospores, polar capsules and other morphological characteristics, together with identification of the site of infection, has led us to propose a novel salmonid-myxobolid species, Myxobolus compostellanus n. sp. Molecular analysis of the small subunit ribosomal RNA (SSU-rRNA) gene yielded the same consensus sequence of 2039 bp in 14 fish specimens. A BLAST search indicated 97.6% similarity to Myxobolus neurobius. Phylogenetic analysis revealed that M. compostellanus n. sp. is clustered with other salmonid-infecting myxobolids. The present findings contribute to the existing knowledge about the genus Myxobolus, providing both morphological and molecular data on a novel species of Myxobolus found to infect the gastrointestinal tract of salmonids, M. compostellanus n. sp. in the brown trout (S. trutta).