A Novel Henneguya Species from Channel Catfish Described by Morphological, Histological, and Molecular Characterization

Channel catfish Ictalurus punctatus from a commercial farming operation in the Mississippi Delta were submitted for examination for the presence of infection by the trematode Bolbophorus damnificus . The fish were instead found to possess skin nodules suggestive of Henneguya pellis , a species previously described in the blue catfish I. furcatus . Despite the dermal location and distribution of lesions, morphological characteristics of the myxospores were inconsistent with H. pellis . Spores possessed a lanceolate spore body 15.4 ± 1.5 μm (mean ± SD; range = 12.2–19.3 μm) in length and 5.5 ± 0.6 μm (range = 4.5–6.8 μm) in width in valvular view, and 4.7 ± 0.2 μm (range = 4.2–5.0 μm) in width in sutural view. Polar capsules were pyriform and unequal in both length and width and contained polar filaments with six coils. Polar capsules measured 6.1 ± 0.8 μm (range = 4.0–7.9 μm) long and 1.7 ± 0.3 μm (range = 1.0–2.2 μm) wide. The caudal appendages were 50.5 ± 8.3 μm (range = 34.8–71.4 μm) long and the total length of the spore was 65.9 ± 8.6 μm (range = 48.2–90.0 μm). The “blisterlike” plasmodia were round or ovoid, up to 2 mm in diameter, and randomly distributed throughout the epidermis of the fish. Histologically, plasmodia were confined to the dermis and elicited no inflammatory reaction from the fish. A blast search of the 18S small subunit rDNA sequence obtained by polymerase chain reaction amplification resulted in no identical sequence matches but indicated a close relationship to H. gurlei , H. ictaluri , and H. exilis . The unique host record, spore morphology, and novel genetic sequence derived from this isolate lead us to propose this isolate as a novel species, H. sutherlandi .