Ultrastructure and molecular diagnosis of Spironucleus salmonis (Diplomonadida) from rainbow trout Oncorhynchus mykiss in Germany

M. Reza Saghari Fard, Anders Jørgensen, Erik Sterud, Wilfrid Bleiss, Sarah L. Poynton

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Diplomonad flagellates infect a wide range of fish hosts in aquaculture and in the wild in North America, Asia and Europe. Intestinal diplomonad infection in juvenile farmed trout can be associated with morbidity and mortality, and in Germany, diplomonads in trout are commonly reported, and yet are poorly characterised. We therefore undertook a comprehensive study of diplomonads from German rainbow trout Oncorhynchus mykiss, using scanning and transmission electron microscopy, and sequencing of the small subunit (ssu) rRNA gene. The diplomonad was identified as Spironucleus salmonis, formerly reported from Germany as Hexamita salmonis. Our new surface morphology studies showed that the cell surface was unadorned and a caudal projection was present. Transmission electron microscopy facilitated new observations of functional morphology, including vacuoles discharging from the body surface, and multi-lobed apices of the nuclei. We suggest the lobes form, via hydrostatic pressure on the nucleoplasm, in response to the beat of the anterior-medial flagella. The lobes serve to intertwine the nuclei, providing stability in the region of the cell exposed to internal mechanical stress. The ssu rRNA gene sequence clearly distinguished S. salmonis from S. barkhanus, S. salmonicida, and S. vortens from fish, and can be used for identification purposes. A 1405 bp sequence of the ssu rRNA gene from S. salmonis was obtained and included in a phylogenetic analysis of a selection of closely related diplomonads, showing that S. salmonis was recovered as sister taxon to S. vortens.

Original languageEnglish (US)
Pages (from-to)37-50
Number of pages14
JournalDiseases of Aquatic Organisms
Issue number1
StatePublished - Mar 29 2007


  • Diagnosis
  • Diplomonad
  • Flagellate
  • Oncorhynchus mykiss
  • Rainbow trout
  • Sequence
  • Spironucleus salmonis
  • Ultrastructure
  • ssu rDNA

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science


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