Location: Warmwater Aquaculture Research UnitTitle: Thelohanellus toyamai infecting the gills of koi Cyprinus carpio in the eastern United States Author
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2010
Publication Date: 6/1/2011
Publication URL: http://handle.nal.usda.gov/10113/55658
Citation: Griffin, M.J., Goodwin, A.E. 2011. Thelohanellus toyamai infecting the gills of koi Cyprinus carpio in the eastern United States. Journal of Parasitology. 97(3):495-502. Interpretive Summary: A myxozoan parasite resembling members of the genus Thelohanellus was isolated from the gills of koi (Cyprinus carpio). DNA analysis of the 18S small subunit ribosomal DNA sequence showed this isolate to be a 99.99% match with the published sequence for Myxobolus toyamai. However, the isolate lacks the characteristic morphological features of Myxobolus and best resembles members of the Theolohanellus. This manuscript provides an ammended morphological description of the agent, supplemented with genetic and histologic data arguing for the organism to be classified as Thelohanellus toyamai (Kudo, 1933) in accordance with the historical classification of the agent.
Technical Abstract: A myxozoan resembling species of Thelohanellus was isolated from the gills of koi (Cyprinus carpio) cultured in North Carolina. Plasmodia measuring ~ 200µm in diameter contained tear-shaped myxospores containing a singly pyriform polar capsule. The spore body was concave on one side, measuring, 16.2 (14.7-16.8) µm ;pmh smf 5.6 (4.5-6) µm wide. The polar capsule was 6.4(5.8-7.2) µm long and 4.2 (3.4-4.6) µm wide, containg a polar filament coiled perpendicular to the longitudinal axis of the spore body making 8 turns. Occasionally, an oblong, irregularly shaped mass of protoplasm was observed between the polar capsule and spore capsule. Analysis of 18S small-subunit ribosomal DNA sequence demonstrated that this isolate as a 99.9% match with Myxobolus toyamai from the gills of C. carpio. However, the case isolate lacked the characteristic second polar capsule of Myxobolus, morphologically placing it within the Thelohanellae. Here, we supplement genetic sequence data with histopathology, an amended morphological description of the agent, and a review of the original classification. For future reference, we suggest this organism be referred to as Thelohanellus toyamai Kudo, 1933, in accordance with the original classification and the nominal M. toyamai be avoided because it is at best outdated and, at worse, incorrect.