Henneguya laseeae n. sp. from flathead catfish (Pylodictis olivaris) in the upper Mississippi River

Synopsis of the species of Henneguya Thélohan, 1892 (Cnidaria: Myxosporea: Myxobolidae) described since 2012

The genus Henneguya Thélohan, 1892 (Cnidaria: Myxosporea: Myxobolidae) encompasses a large number of species that mostly infect freshwater fish belonging to 71 families of Actinopterygii. A synopsis of Henneguya species described between 2012 and 2022 is herein presented. It includes 57 species described during the last decade, and one species missing from the previous synopses, adding to a total of 254 species that have been formally described within this genus. Biological characters and myxospore morphometry are presented for each species record.

New data on Henneguya postexilis Minchew, 1977, a parasite of channel catfish Ictalurus punctatus, with notes on resolution of molecular markers for myxozoan phylogeny

Previous morphological and histological data are supplemented with molecular and ultrastructural data for a Henneguya sp. isolated from farm-raised channel catfish Ictalurus punctatus in Mississippi, USA. Myxospores were cryptic, encapsulated within a thin layer of epithelium in the gill lamellae with spore measurements consistent with the original description of Henneguya postexilis Minchew, 1977. Myxospores were 42.7-49.1 µm in total length with spore bodies 12.1-17.2 × 3.6-4.8 × 2.9-3 µm. Polar capsules were of unequal length, with the longer capsule being 4.4-6.7 × 1.1-1.6 µm and the shorter capsule being 4.4-6.4 × 1.1-1.6 µm. Polar tubules had 6-8 turns. Caudal processes were 25.7-38.1 µm in length. Spores were encapsulated in a thin layer of epithelium in the gill lamellae. Molecular data from the most commonly used markers for myxozoan identification and phylogeny, partial 18S small subunit ribosomal gene (SSU), partial 28S large subunit ribosomal gene (LSU), and elongation factor 2 (EF2) were generated for H. postexilis. Additionally, novel data for LSU and EF2 were generated for archived myxozoan specimens from farm-raised catfish (H. mississippiensis, H. ictaluri, H. exilis, H. adiposa, H. sutherlandi, H. bulbosus, Unicauda fimbrethilae), as well as archived specimens from wild fish (H. laseeae [from Pylodictis olivaris], Hennegoides flockae [from Aphredoderus sayanus], Myxobolus cloutmani [from Cycleptus elongatus]. These include the first EF2 sequence data for the genera Hennegoides and Unicauda. Phylogenetic analyses using these data placed H. postexilis in well supported clades with other ictalurid-infecting Henneguya species. Phylogenetic signal assessments on these analyses suggest that while SSU provided the greatest phylogenetic signal, LSU yielded comparable signal, supporting previous work implying this region may be underutilised in reconstructing myxobolid phylogenies.

Phylogeny and ultrastructure of Henneguya fusiformis Kostoïngué, Fall, Faye and Toguebaye 1999, a newly recorded species infecting the ovaries of Clarias gariepinus in Egypt

The genus Henneguya is the second largest within the class Myxosporea, which infects marine and freshwater fish. One hundred Clarias gariepinus specimens were collected alive from a branch of the Nile River in Kafrelsheikh, Egypt. Microscopic and molecular procedures were used to describe how Henneguya fusiformis infects the ovaries of C. gariepinus. The infected fish showed no pathogenic changes except for macroscopic creamy whitish nodules in their ovaries with the highest prevalence during the spring season. The mature spores are spindle-shaped. The total spore length, spore body length and width are 53.4 ± 0.8 (52.5-54.3) µm, 29.8 ± 0.5 (29.2-30.4) µm and 6.5 ± 0.3 (6.1-6.9) µm, respectively. The spore anterior end consisted of two equal polar capsules, located in a tandem position, each one measuring 4.2 × 2.1 µm. The polar filament formed a coil with 6-8 turns. The measurement of the spore end with two extended processes was 24.3 ± 0.4 (23.9-24.8) µm. Phylogenetic analyses of the 18S ribosomal RNA gene sequence revealed that H. fusiformis are clustered together with other myxobolids that are histozoic in channel catfish, Ictalurus punctatus, and Asian Redtail catfish, Hemibagrus nemurus" (Clariidae) in the United States and Malaysia, respectively. To the best of our knowledge, this is the first record of H. fusiformis in Egypt. Additionally, our study is the first record of H. fusiformis in the ovaries of C. gariepinus.

Henneguya michiganensis n. sp. (Cnidaria: Myxosporea) from the gills of muskellunge Esox masquinongy Mitchill(Esociformes: Esocidae)

Henneguya Thélohan, 1892 is the second most species rich genus of myxozoans, with reports from freshwater and marine fish worldwide. In the Great Lakes region of North America, muskellunge Esox masquinongy is an important game fish species that serves as an apex predator in the ecosystems of many inland lakes. The myxozoan fauna of esocid fish, especially muskellunge, remains largely understudied. During fish health assessments, muskellunge were examined for parasitic infections and myxozoan pseudocysts were observed on gill clip wet mounts. When ruptured under pressure, the intralamellar pseudocysts released thousands of myxospores consistent with those of the genus Henneguya. The myxospores were 67.3-96.6 (79.1 ± 5.9) µm in total length. The spore body was 18.6-22.6 (20.9 ± 1.0) µm × 5.4-6.9 (6.3 ± 0.4) µm in valvular view and 3.5-4.0 (3.8 ± 0.3) µm wide in sutural view. The two pyriform polar capsules positioned at the anterior of the spore body were 6.4-7.7 (7.0 ± 0.4) µm × 1.8-2.1 (2.0 ± 0.1) µm and each contained a tightly coiled polar filament with 9-10 turns. Two tapering caudal processes extended from the posterior of the spore body and were 47.3-75.6 (58.3 ± 5.8) µm in length. Histologically, large intralamellar polysporic plasmodia were surrounded by plump pillar cells and a distinct layer of plasma. Mild inflammation was present peripherally, with small numbers of necrotic germinative cells and intraplasmodial phagocytes internally. Ribosomal 18S rRNA gene sequence data were obtained from three gill pseudocysts. The three ~2000-bp sequences were identical, but shared no significant similarity with any publicly available sequence data. Phylogenetic analyses demonstrated sequence data from this Henneguya fell within a well-supported clade of Henneguya spp. reported from northern pike Esox lucius in Europe. Based on the distinct morphological, histological and molecular data, this species is designated as Henneguya michiganensis n. sp. from muskellunge in Michigan, USA.

A new species of Myxosporea, Henneguya quelen, from silver catfish Rhamdia quelen (Siluriforme: Pimelodidae) in the Amazonian region

Henneguya quelen n. sp. (Myxosporea) is described from the kidney of the silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), from Marajó Island. In all, 40% of the 57 silver catfish collected from the Paracauari River in the municipality of Salvaterra presented cysts in the kidney. The cysts were whitish, spherical, and 0.45 mm in diameter. The histological analyses revealed tubular renal compression and cellular degeneration in the area adjacent to the xenomas. The spores are ellipsoid, with well-marked valves, caudal projection, and two elongated polar capsules of equal size. The mature spores measure approximately 15.6 μm in length, with the caudal appendage split posteriorly; 24.3 μm in length, for a total spore length of 40.0 μm; and a width of 4.1 μm. The polar capsules are pyriform, 5.5 μm long and 1.7 μm wide. A phylogenetic analysis based on Bayesian inference confirmed that the specimens represented a new species, which was denominated Henneguya quelen n. sp.