H. salminicola

From Fish
Trunk muscle of pink salmon infected with Henneguya
Lesions caused by H. salminicola
Fresh spores of Henneguya salminicola

Henneguya salminicola (Taxonomy: Myxozoa, Myxosporea, Bivalvulida) is a myxosporidian parasite of the trunk muscles of various marine fish.

They parasitize a wide variety of fish tissues, where they often produce pseudocysts which contain hundreds of thousands of small spores. H. salminicola is a histozoic species that produces pseudocysts within striated muscle of salmonid fishes throughout the northern hemisphere[1][2]. Spores such as those of H. salminicola are chitinized and are known to pass intact through the vertebrate gut[3].

Hosts include Coho salmon (Oncorhynchus kisutch), Chinook salmon (Oncorhynchus tshawytscha), Pink salmon (Oncorhynchus gorbuscha), Sockeye salmon (Oncorhynchus nerka), Chum salmon (Oncorhynchus keta) and Rainbow trout (Oncorhynchus mykiss).

Life cycle

Cysts are filled with a number of spermatozoa-like spores. A spore (average length 10.7 μm; average width 8.7 μm; average thickness 6.1μm) is oval and has 2 slightly unequal polar capsules (larger one: average length 4.2 μm; average width 2.5 μm, smaller one: 3.8 μm; 2.2 μm) and 2 caudal appendages (longer one: average length 34.8 μm, shorter one: 28.9 μm). The life cycle is unknown. The alternate host is probably involved in the life cycle. The parasite encapsulates within the host’s connective tissues and forms cysts[4].

Clinical signs

White cysts (a few mm) are observed in the trunk muscle. In the frozen fish or smoked fish, the site of infection looks like a milky condition[5].

Since this parasite is not infectious to human, it is harmless in food hygiene.

Diagnosis

Diagnosis is based on visual observation of spermatozoa-like spores by wet-mount smears of degenerated muscle tissue. Sample should be smeared and stained by Giemsa.

References

  1. Margolis, L., and J. R. Arthur. (1979) Synopsis of the parasites of fishes of Canada. Bull Fish Res Board Can 199:1–269
  2. McDonald, T. E., and L. Margolis. (1995) Synopsis of the parasites of fishes of Canada: supplement (1978–1993). Can Spec Publ Fish Aquat Sci 122:1–265
  3. El-Matbouli, M., T. Fischer-Scherl, and R. W. Hoffman. (1992) Present knowledge of the life cycle, taxonomy, pathology, and therapy of some Myxosporea spp. important for freshwater fish. Ann Rev Fish Dis 2:367–402
  4. Lom, J. and I. Dykova (1992) Protozoan parasites of fishes. Elsevier, New York, p:315
  5. Awakura T. and T. Kimura (1977) On the milky condition in smoked coho salmon (Oncorhynchus kisutch) caused by myxosporidian parasite. Fish Pathol 12:179-184