Myxobolus albi infection in cartilage of captive lumpfish (Cyclopterus lumpus).

Myxobolus albi was diagnosed in the cartilage of captive lumpfish (Cyclopterus lumpus) from 2 public aquaria. Eleven fish were affected, with the most common clinical signs being exophthalmos and grossly visible 1- to 2-mm white to tan scleral nodules. Myxozoan cysts were identified in the cartilage of the skull, branchial arch, sclera, vertebrae, tongue, all fin insertions, and the pectoral girdle. Cysts resulted in expansile, deforming, space-occupying lesions, resulting in exophthalmos but often lacking significant tissue damage or inflammation. Once cysts ruptured, free spores elicited a mild to marked inflammatory response. Spores measured 7.5 to 9.0 µm × 3.0 to 6.0 µm and contained 2 pyriform polar capsules oriented at one pole as well as occasional 1-µm-diameter basophilic nuclei. Identification was based on spore morphology together with polymerase chain reaction and sequence comparison of 18S ribosomal DNA. Isolates had 99% similarity to M. albi.