Pathologic Changes Associated With Respiratory Compromise And Morbidity Due To Massive Interlamellar Henneguya Exilis Infection In Channel × Blue Hybrid Catfish.

There are multiple Henneguya spp. (Myxozoa: Myxobolidae) endemic to North American catfish aquaculture that affect the gills of channel catfish and their hybrids. These parasites are morphologically similar, and confusion exists regarding the predilection sites and pathologic changes associated with different species. In the spring of 2018, channel (Ictalurus punctatus) female × blue (Ictalurus furcatus) male hybrid catfish from 2 separate commercial operations in northwest Mississippi were submitted for diagnostic assessment in response to observed morbidity and reduced feeding activity. Fish presented with unusually heavy infections of Henneguya spp. plasmodia in the gills. The majority of gill filaments contained widespread, pinpoint, raised, white nodules corresponding microscopically to myxospore-filled plasmodia that obliterated interlamellar spaces. The bipolar myxospores were consistent with Henneguya spp. described from North American ictalurids, possessing slender fusiform spore bodies and elongate bifurcate caudal processes. Associated microscopic lesions included lamellar fusion, epithelial hyperplasia, infrequent, localized, granulomatous branchitis, and rare cartilage lysis, suggesting impaired gill function. Mature plasmodia were excised by laser capture microdissection from ethanol-fixed, hematoxylin and eosin-stained histologic sections for molecular analysis. Fragments (700 bp) of a highly variable region of the 18S rRNA gene, diagnostic for the Myxobolidae, were 100% similar at the nucleotide level to Henneguya exilis. Although mortality was negligible, fish in the affected ponds exhibited signs of respiratory distress similar to proliferative gill disease (PGD) caused by Henneguya ictaluri in channel and hybrid catfish. However, gross and microscopic lesions differed markedly from PGD, known colloquially as "hamburger gill disease." While H. exilis has been reported from channel catfish, it is not typically associated with morbidity and mortality and has not previously been reported from channel × blue catfish hybrids. This work characterizes lesions and confirms the etiology of gill disease induced by the myxozoan H. exilis. In addition to PGD and other non-parasitic conditions, massive interlamellar H. exilis infection should be a differential consideration in pond-raised channel and hybrid catfish experiencing signs of respiratory distress.

Small subunit ribosomal RNA sequence links the myxospore stage of Henneguya mississippiensis n. sp. from channel catfish Ictalurus punctatus to an actinospore released by the benthic oligochaete Dero digitata.

There are more than 200 species of Henneguya described from fish. Of these, only three life cycles have been determined, identifying the actinospore and myxospore stages from their respective hosts. Two of these life cycles involve the channel catfish (Ictalurus punctatus) and the freshwater oligochaete Dero digitata. Herein, we molecularly confirm the life cycle of a previously undescribed Henneguya sp. by matching 18S ribosomal RNA (rRNA) gene sequence of the myxospore stage from channel catfish with the previously described actinospore stage (Aurantiactinomyxon mississippiensis) from D. digitata. Gill tissue from naturally infected channel catfish contained pseudocysts restricted to the apical end of the primary lamellae. Myxospores were morphologically consistent with Henneguya spp. from ictalurid fishes in North America. The spores measured 48.8 ± 4.8 µm (range = 40.7-61.6 µm) in total spore length. The lanceolate spore body was 17.1 ± 1.0 µm (14.4-19.3 µm) in length and 5.0 ± 0.3 µm (4.5-5.5 µm) in width. The two polar capsules were 6.2 ± 0.4 µm (5.8-7.0 µm) long and 5.0 ± 0.3 µm (4.5-5.5 µm) wide. The polar capsule contained eight to nine coils in the polar filament. The two caudal processes were of equal length, measuring 31.0 ± 4.1 µm (22.9-40.6 µm). The 1980-bp 18S rRNA gene sequence obtained from two excised cysts shared 99.4% similarity (100% coverage) to the published sequence of A. mississippiensis, an actinospore previously described from D. digitata. The sequence similarity between the myxospore from channel catfish and actinospore from D. digitata suggests that they are conspecific, representing alternate life stages of Henneguya mississippiensis n. sp.

18S rRNA gene sequencing identifies a novel species of Henneguya parasitizing the gills of the channel catfish (Ictaluridae).

In the southeastern USA, the channel catfish Ictalurus punctatus is a host to at least eight different species of myxozoan parasites belonging to the genus Henneguya, four of which have been characterized molecularly using sequencing of the small subunit ribosomal RNA (SSU rRNA) gene. However, only two of these have confirmed life cycles that involve the oligochaete Dero digitata as the definitive host. During a health screening of farm-raised channel catfish, several fish presented with deformed primary lamellae. Lamellae harbored large, nodular, white pseudocysts 1.25 mm in diameter, and upon rupturing, these pseudocysts released Henneguya myxospores, with a typical lanceolate-shaped spore body, measuring 17.1 ± 1.0 µm (mean ± SD; range = 15.0-19.3 µm) in length and 4.8 ± 0.4 µm (3.7-5.6 µm) in width. Pyriform-shaped polar capsules were 5.8 ± 0.3 µm in length (5.1-6.4 µm) and 1.7 ± 0.1 µm (1.4-1.9 µm) in width. The two caudal processes were 40.0 ± 5.1 µm in length (29.5-50.0 µm) with a spore length of 57.2 ± 4.7 (46.8-66.8 µm). The contiguous SSU rRNA gene sequence obtained from myxospores of five excised cysts did not match any Henneguya sp. in GenBank. The greatest sequence homology (91% over 1,900 bp) was with Henneguya pellis, associated with blister-like lesions on the skin of blue catfish Ictalurus furcatus. Based on the unique combination of pseudocyst and myxospore morphology, tissue location, host, and SSU rRNA gene sequence data, we report this isolate to be a previously unreported species, Henneguya bulbosus sp. nov.

Iron status of channel catfish Ictalurus punctatus affected by channel catfish anemia and response to parenteral iron.

Originally reported in 1983, channel catfish anemia (CCA), also 'white lip' or 'no blood,' is a major idiopathic disease affecting commercial production in the Mississippi Delta region of the USA. Affected individuals are characterized by lethargy, anorexia, extreme pallor, and packed cell volumes often below 5%, but a definitive cause for CCA remains elusive. Records from the National Warmwater Aquaculture Center (NWAC) reveal that, on average, CCA accounted for 4.7% of case submissions from 1994 to 2012. Known infectious agents, parasites, and perturbations in commonly measured water quality variables have been largely excluded, and research has focused on potential feed-related etiologies, particularly folic acid deficiency. No natural or anthropogenic contaminants have been found in feeds, and no associations have been made to any particular feed brand or formulation, or to the age or condition of the feed itself. Contrary to reports indicating a short clinical course, NWAC records indicate an insidious condition where certain ponds have contained fish diagnosed with CCA for up to 4 consecutive years and individual outbreaks have persisted for at least 5 mo. Investigation into the iron status of CCA-affected fish revealed values consistent with iron deficiency anemia, including low-packed cell volume (mean ± SE, 5.6 ± 1.0 vs. 24.8 ± 2.4%), serum iron (35.2 ± 3.5 vs. 104.4 ± 18.5 µg dl-1), liver iron (12.2 ± 2.6 vs. 23.3 ± 4.6 µg g-1), and percent transferrin saturation (14.5 ± 2.7 vs. 26.9 ± 3.1%) in anemic and healthy controls, respectively. Administration of parenteral iron produced complete recovery and returned iron indices to within the ranges of normal controls. Despite these findings, factors predisposing a state of hypoferremia remain unknown.

New data on Henneguya pellis (Myxozoa: Myxobolidae), a parasite of blue catfish Ictalurus furcatus.

The original description of Henneguya pellis, a myxozoan parasitizing blue catfish Ictalurus furcatus, is supplemented with new data on histopathology, spore morphology, and 18S small subunit (SSU) ribosomal DNA (rDNA) sequence. Plasmodia presented as both internal and external, raised, cyst-like lesions on the body wall of the peritoneal cavity and on the skin. The cysts contained numerous elongate, lanceolate myxospores, flattened parallel to the suture line. The spore body was 14.8 ± 1.1 µm (range 13.0-17.1) long and 4.8 ± 0.8 µm (range 4.0-7.4) wide in frontal view. The caudal appendages were 77.7 ± 8.8 (range 57.4-96.4) in length. There were 2 pyriform polar capsules, unequal in length, with the longer capsule measuring 7.2 ± 0.6 µm (range 6.2-8.4) in length and the shorter capsule measuring 6.5 ± 0.5 µm (range 5.5-8.0). The polar capsules were not significantly different in width, measuring 1.7 ± 0.2 µm (range 1.4-1.9). There were 8 turns in the polar filament coil. The total length of the spore was 92.5 ± 9.2 µm (range 73.3-113.5). Spore morphology and site of development are similar to that of Henneguya sutherlandi from channel catfish; however, 18S rDNA sequence data support previous findings that identify H. pellis and H. sutherlandi as 2 distinct species.