Ultrastructure of Spironucleus barkhanus N. Sp. (Diplomonadida: Hexamitidae) from Grayling Thymallus thymallus (L.) (Salmonidae) and Atlantic Salmon Salmo salar L. (Salmonidae)

Abstract

A hexamitid flagellate Spironucleus burkhanus n. sp., from the lumen of the gut and gall bladder of wild grayling Thymullus thymallus, and from muscle abscesses of farmed Atlantic salmon Salmo salar from Norway, is described by light, scanning and transmission electron microscopy. The flagellate was axenically cultured in trypticase, yeast extract, iron serum medium. Live trophozoites from axenic cultures incubated at 5" C , measure 11-20 X 6-14 p n . The flagellates show a typical bi-radial symmetry. Each recurrent flagellum is almost completely surrounded by a striated lamina. In the posterior end the lamina widens, appearing heart shaped in transverse section. Accompanying each recurrent flagellum are three narrow bands of microtubules, following the longitudinal groove created by the incomplete closure of the striated lamina. The recurrent flagella emerge posterio-medially through cytostome openings halfway surrounded by crescent-shaped ridges, oriented in opposite directions in the two openings. The position and adornment of the cytostome openings, and the arrangement and number of the microtubules accompanying the recurrent flagella, distinguish Spironucleus barkhanus n. sp. from previously described species of Spironucleus.Supplementary key words. Axenic culture, Hexamifa, systemic infection. URING a parasite survey in the autumn of 1989, a hex-Received 11- 5-97, 2-24-97; accepted 4-28-97

In vitro cultivation and temperature-dependent growth of two strains of Spironucleus barkhanus (Diplomonadida:Hexamitidae) from Atlantic salmon Salmo salar and grayling Thymallus thymallus

“…The different temperature responses seen in the 2 strains is not incompatible with the conclusions of Sterud et al (1997) that these strains are the same species. Different temperature responses between races/clones of a single species is well known in freeliving protists, and no single clone or strain should be considered to be representative of an entire species (Granskog 1991).…”

“…The fish were severely affected, and in the Norwegian cases, the hexamitid flagellates were abundant in necrotic lesions in the muscles and internal organs. The flagellate, first believed to be Hexamita salmonis Moore, 1922, was described as Spironucleus barkhanus by Sterud et al (1997), who also found the flagellate in grayling Thymallus thymallus ( L . ) from southeastern Norway.…”

Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)

“…However, in Spironucleus barkhanus, which has three microtubular bands, only one of the bands is continuous with R1; the other two derive from the indirect fibre of the opposite kinetid (compare Fig. 6a and c in Sterud et al, 1997), indicating that a split R1 is not universal in diplomonads.…”

“…It is possible that this structure is homologous to the singlet roots of other excavate taxa. However, Spironucleus barkhanus, at least, seems to lack singlet microtubular roots, as all relevant microtubules appear to be continuous with either the right root or the indirect fibre (compare Figs 6a and c in Sterud et al, 1997).…”

Wild Arctic char Salvelinus alpinus and trout Salmo trutta: hosts and reservoir of the salmonid pathogen Spironucleus salmonicida (Diplomonadida; Hexamitidae)

“…Sterud et al (1997) presented a scanning and transmission electron microscopy (SEM and TEM) study of hexamitid flagellates from farmed Atlantic salmon with systemic infection where ultrastructural data showed that the hexamitid flagellate causing systemic disease in farmed Atlantic salmon was different from H. salmonis. The ultrastructural features of the studied hexamitid flagellate were consistent with those of the genus Spironucleus.…”