Location: Warmwater Aquaculture Research UnitTitle: Molecular Characterization and Histopathology of Myxobolus koi Infecting the Gills of A koi Cyprinus carpio, with an Amended Morphologic Description of the Agent Author
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2009
Publication Date: 2/14/2010
Publication URL: http://handle.nal.usda.gov/10113/55485
Citation: Camus, A.C., Griffin, M.J. 2010. Molecular Characterization and Histopathology of Myxobolus koi Infecting the Gills of A koi Cyprinus carpio, with an Amended Morphologic Description of the Agent. Journal of Parasitology. 96:116-124. Interpretive Summary: With its worldwide introduction to temperate waters as a food and ornamental fish, the common carp (koi), Cyprinus carpio, has become one of the most widely distributed freshwater fish species in North America. As such, an in depth knowledge of pathogens affecting koi is of significant importance to fisheries biologists and fish health professionals. Through diagnostic case submissions we have characterized a myxozoan parasite infecting koi for future reference in monitoring pathogens that may be introduced in other species of domestically produced fish.
Technical Abstract: A Myxobolus sp., morphologically resembling M. toyamai, M. longisporus, and M. koi, was isolated from the gills of a koi, Cyprinus carpio that died in an ornamental pond. Large plasmodia were localized within lamellae, causing severe disruption of the normal branchial architecture, sufficient to compromise respiration. Although the case isolate shared several features with the aforementioned species, several key characteristics were most compatible with M. koi. In valvular view, spores were elongate and pyriform with a rounded posterior, 15.4 (14.5–16.5) mm long and 8.3 (7.1–9.0) mm wide. Polar capsules were pyriform and elongate, 10.1 (9.0–10.9) mm long and 3.1 (2.5–3.5) mm wide. Polar filaments were coiled perpendicular to the long axis of the spore making 10 turns (9–11). A BLAST search using a generated 18S SSU rDNA sequence resulted in no direct matches. Phylogenetic analysis of the sequence indicates a close relationship to M. longisporus and M. toyamai from C. carpio, within the clade of Myxobolus species infecting gills of cyprinid fishes (89% or greater bootstrap support by maximum parsimony and minimum evolution distance analysis). Although published descriptions are inconsistent, morphometric similarities to this isolate suggest a morphotype of M. koi. The description of M. koi is supplemented here with new data on pathogenicity and spore morphology and is characterized at the molecular level using 18S small subunit rDNA sequence data.