Infection of Aulorhynchus flavidus (Gill) (Osteichthyes: Gasterosteiformes) by Kudoa thyrsites (Gilchrist) (Myxosporea: Multivalvulida).

The myxosporean parasite Kudoa thyrsites is reported from a new host, Aulorhynchus flavidus, the tube-snout, collected near Vancouver, British Columbia, Canada. Prevalence reached 100% and intensity 1,535 pseudocysts per 2 cm length of fish. Polymerase chain reaction primers specific for K. thyrsites amplified a fragment of the small subunit rDNA and confirmed identification. These primers also allowed detection of K. thyrsites in young (< 4-mo-old) fish with no other apparent sign of infection. No inflammatory response or liquefaction of host tissue was associated with the infection. The number of pseudocysts per infected fish was not correlated with fish size or condition, although larger fish (total length) had larger pseudocysts (rs = 0.437, P < 0.001). This finding brings to 28 the number of potential hosts for the species. Kudoa thyrsites is a well recognized cause of soft flesh in netpen-reared Atlantic salmon in coastal waters of British Columbia. Tube-snouts are common in and around these netpens, and thus may be a significant host reservoir for K. thyrsites.

Ribosomal DNA sequence of Nucleospora salmonis Hedrick, Groff and Baxa, 1991 (Microsporea:Enterocytozoonidae): implications for phylogeny and nomenclature.

Rules of zoological nomenclature, morphological data, and ribosomal DNA sequence data support the validity of the genus Nucleospora, and its placement in the family Enterocytozoonidae. Although Nucleospora exhibits most of the distinguishing morphological characteristics of the family Enterocytozoonidae Cali and Owen, 1990, the distinctively different hosts (fish and humans, respectively) and sites of development (the nuclei of immature blood cells and the cytoplasm of enterocytes) support the placement of Nucleospora and Enterocytozoon into separate genera. Ribosomal DNA sequence comparisons between Nucleospora salmonis and Enterocytozoon bieneusi showed 19.8% genetic divergence in the large and small subunit regions. Although more inter- and intrageneric comparisons are needed before percent homology of ribosomal DNA can be used as a criterion for the separation of genera, the genetic divergence between the two species is sufficiently large to deter suppression of the genus Nucleospora as a junior synonym of Enterocytozoon. A polymerase chain reaction test for the detection of N. salmonis in chinook salmon (Oncorhynchus tshawytscha), based on N. salmonis-specific ribosomal DNA sequence, is described.