Location: Warmwater Aquaculture Research UnitTitle: Theohanellus 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: 6/15/2011
Citation: Griffin, M.J., Goodwin, A.E. 2011. Theohanellus toyamai infecting the gills of Koi cyprinus carpio in the Eastern United States. Journal of Parasitology. 97(3):493-502. Interpretive Summary: The manuscript describes a myxozoan parasite that was found in the gills of koi from North Carolina. The spore morphology places it in the Thelohanellus but its sequence of the 18S small ribosomal DNA was a 99.9% matched to a published sequence for Myxobolus toyamai. However, the case isolate for later did not have a second polar capsule which is found in Myxobolus. It was thus suggested that this parasite be referred to as Thelohanellus toyamai rather than M. toyamai in the future.
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 single pyriform polar capsule. The spore body was concave on one side, measuring 16.2 (14.7 – 16.8)µm long and 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, containing a polar filament coiled perpendicular to the longitudinal axis of the spore body making 8 turns. Occasionally, an oblong, irregular shaped mass of protoplasm was observed between the polar capsule and spore capsule. Analysis of the 18S small-subunit ribosomal DNA sequence demonstrated 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 Thelohanellus. Here we supplement genetic sequence data with histopathology, an amended morphological description of the agent, and a review of the original classification. For future references, 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Kudo, 1933, in accordance with the original classification and the nominal M. toyamai be avoided because it is at best outdated and, at worse, incorrect.