Verrucous dermal henneguyosis associated with Henneguya exilis (Kudo, 1929) (Cnidaria: Myxobolidae), a parasite of the channel catfish Ictalurus punctatus (Rafinesque, 1818)

Necroulcerative dermatitis associated with Myxobolus dermatoulcerans n. sp. (Cnidaria: Myxobolidae) in red-bellied piranha, Pygocentrus nattereri Kner (Characiformes: Serrasalmidae), from Peru

A group of red-bellied piranha, Pygocentrus nattereri Kner, recently imported from Peru exhibited multifocal, cutaneous ulcerations with exposure of the underlying musculature. Skin scrapes yielded moderate numbers of myxospores morphologically consistent with Myxobolus Bütschli, 1882. Myxospores from these fish were morphologically and molecularly distinct from other myxobolids infecting piranha. Myxospores are pyriform to capsular with a rounded posterior and slightly rounded to tapering anterior aspect in valvular view. Myxospore bodies are 14.3-17.8 (mean 16.1) µm long and 7.6-10.3 (mean 8.9) µm wide. Polar capsules are symmetrical, slender, elongate, and measure 7.4-10.2 (mean 9.2) µm long and 2.1-3.7 (mean 3.0) µm wide. Sequence generated for the 18S rRNA gene had no direct matches to any sequence available on GenBank but demonstrated less than 89% nucleotide similarity to various published and unpublished Myxobolus spp. from Piaractus brachypomus (Cuvier) and Colossoma macropomum (Cuvier). This paper provides the morphological and molecular characterisation of Myxobolus dermatoulcerans n. sp. from red-bellied piranha and describes associated pathological lesions.

A morphological, molecular, and histopathological redescription of Henneguya nyongensis Fomena & Bouix, 1996 (Cnidaria: Myxobolidae) infecting the gills of Peter's elephantnose fish, Gnathonemus petersii (Günther) (Osteoglossiformes: Mormyridae), imported from Nigeria

A Henneguya sp., morphologically resembling Henneguya nyongensis Fomena & Bouix, 1996, was isolated from the gills of Peter's elephantnose fish, Gnathonemus petersii Günther, imported from Nigeria. Plasmodia were located between lamellae and within the gill epithelium, often leading to lamellar fusion. Although slightly smaller, the myxospores from these fish were morphologically consistent with H. nyongensis. In valvular view, spores are elongate, pyriform with a rounded posterior and tapering caudal processes. Myxospore bodies are 9.6-12.3 (mean 11.2) µm long and 4.0-4.7 (mean 4.3) µm wide. Polar capsules are pyriform, elongate, 4.5-5.2 (4.7) µm long and 1.3-1.6 (1.4) µm wide, with a characteristic neck-like structure at the apical end. Sequence generated for the 18S small subunit rRNA gene did not directly match any sequences available on GenBank, but demonstrated 91% nucleotide similarity to an unpublished Henneguya sp. infecting Mormyrus kannume Forsskål. Herein, the description of H. nyongensis is supplemented with new data on histopathology, molecular characterisation, and expanded host and geographical range.

Arrested Development of Henneguya ictaluri (Cnidaria: Myxobolidae) in ♀ Channel Catfish × ♂ Blue Catfish Hybrids

Henneguya ictaluri is the etiologic agent of proliferative gill disease (PGD) in farm-raised Channel Catfish Ictalurus punctatus and hybrid catfish in the southeastern United States, and significant annual losses are attributed to this disease. Research suggests that H. ictaluri infection dynamics in Blue Catfish I. furcatus and hybrid catfish (Channel Catfish × Blue Catfish) differ from those in Channel Catfish. Two separate infectivity trials were conducted to investigate H. ictaluri development in Channel Catfish, Blue Catfish, and their hybrids. On two separate occasions with two different year-classes, fish were exposed to pond water containing H. ictaluri actinospores and sampled weekly for 12 weeks (trial 1) or 14 weeks (trial 2). In trial 1, the presence of H. ictaluri was evaluated histologically and by quantitative PCR of fish tissues, including gills, blood, anterior kidney, brain, heart, liver, posterior kidney, spleen, and stomach. Henneguya ictaluri DNA was detected in significantly higher concentrations throughout multiple organ systems in the Channel Catfish compared to the hybrid catfish and Blue Catfish, with the gills having higher quantities. Myxospores were observed in Channel Catfish gill tissue at 8 weeks postexposure. No myxospores were observed in Blue Catfish or hybrid catfish. The second trial focused on gills only and yielded similar results, with Channel Catfish having significantly greater H. ictaluri DNA quantities than hybrids or Blue Catfish across all time points. Myxospores were observed in Channel Catfish beginning at 6 weeks postexposure and were found in 36% (58/162) of Channel Catfish sampled for molecular and histological analysis during weeks 6-14. Myxospores in hybrid catfish were sparse, with single pseudocysts observed in two hybrid catfish (1.2%) at 14 weeks postexposure. These results imply arrested development of H. ictaluri in hybrid catfish. As such, culture of hybrid catfish may be an effective management strategy to minimize the burden of PGD.

Molecular confirmation of Henneguya adiposa (Cnidaria: Myxozoa) and associated histologic changes in adipose fins of channel catfish, Ictalurus punctatus (Teleost)

Henneguya adiposa is one of ten known, closely related myxozoan species that parasitize a variety of tissue sites in the channel catfish, Ictalurus punctatus. Reported to specifically target the adipose fin, H. adiposa is not associated with morbidity or mortality, although detailed descriptions of its associated histologic pathology are lacking. The objective of this work was to confirm the presence of H. adiposa within fin lesions of affected channel catfish using DNA sequenced from histologic sections obtained by laser capture microdissection, as well as to describe pathologic changes induced by infection. The parasite formed large, white, elongate, nodular plasmodia that caused localized tissue damage and incited a granulomatous inflammatory response within a deep connective tissue layer at the base of the adipose fin. Myxospores released from ruptured plasmodia into adjacent tissue were observed to migrate superficially in tracts through the skin, indicating a portal of exit for environmental dispersal. Defects in the connective tissue layer created by ruptured plasmodia were infiltrated by granulomatous inflammation and fibroplasia, suggesting lesion resolution by scar formation over time. Sequencing of the 18S rRNA gene amplified from excised myxospores confirmed the myxozoan's identity as H. adiposa, with 100% similarity to the reference sequence from previous published work.