Henneguya postexilis Minchew, 1977

Nitta, Masato & Ishikawa, Takanori, 2024, New Japanese Record of Henneguya postexilis (Cnidaria: Myxobolidae) from Gills of Alien Channel Catfish Ictalurus punctatus (Siluriformes: Ictaluridae) in Japan, Species Diversity 29 (1), pp. 23-30 : 25-27

Henneguya postexilis Minchew, 1977

[New Japanese name: Amerika-namazu-uchiwa-mushi] ( Figs 1 , 2 )

Henneguya postexilis Minchew, 1977: 219 , figs 49–64, 73, 74; Lom and Dyková 1992: 298; Hoffman 1999: 65; Eiras 2002: 46; Wagner 2016: 76; Woodyard et al. 2022: 47–48, figs 1–4, 7–10; Zhang et al. 2023: 5–6, fig. 5.

Specimens. MPM Coll.-No. 25259.

Description. Plasmodium oblong, 82.8–115.7 (94.3 ±13.8, n=5) long, 121.8–200. 5 (169.1±29.3, n=5) wide. Total length of myxospore including caudal processes 45.7–69.9 (56.2±6.3, n=51). Spore body lanceolate, 12.9–17.9 (14.9 ±1.1, n=137) long, 3.2–4.4 (3.8±0.3, n=83) wide, length: width ratio 1:0.20–0.34 (0.26±0.03, n=83), thickness 2.8–3.8 (3.4±0.2, n =55). Pair of caudal process, equal in length, 29.4–54.4 (41.3 ±6.4, n=51). Pair of polar capsules pyriform, occupying anterior half of spore body, mostly unequal in length, with 6–9 (7.2±0.8, n=67) polar tubule turns. Longer polar capsule 5.3–7.5 (6.4±0.4, n=80) long, 0.9–1.6 (1.2 ±0.2, n=80) wide; shorter polar capsule 4.9–6.8 (5.9±0.5, n=80) long, 0.8–1.7 (1.2±0.2, n=80) wide; length ratio of longer and shorter polar capsule 1:0.75–0.99 (0.93 ±0.05, n= 80).

Locality. Omoi River (36°17′18.1″N, 139°46′18.7″E), Tone River system, in Oyama City, Tochigi Prefecture, Japan .

Host. Ictalurus punctatus (Rafinesque, 1818) ( Siluriformes : Ictaluridae ).

Site of infection. Gill filaments.

Japanese name. The new Japanese name, “amerikanamazu” refers to the host, Ictalurus Rafinesque, 1820 , in Japanese, and “uchiwa-mushi” means the genus Henneguya .

Molecular data comparison. A BLASTn analysis of the newly obtained 18S rDNA fragment (1894 bp; LC781947) returned a 100% match of H. postexilis [MZ905344, Woodyard et al. (2022) from USA; MK811030, Zhang et al. (2023) from China] with 100% and 99% coverage, respectively.

Phylogenetic analysis. The newly obtained sequence was placed in a clade with the other H. postexilis sequences (MZ905344, MK811030). This species formed a sister clade with a clade of H. ictalurid Pote, Hanson, and Shivji, 2000 , H. mississippiensis Rosser, Griffin, Quiniou, Khoo, Greenway, Wise, and Pote, 2015 , and Helioactinomyxon sp.

Remarks. Henneguya postexilis was originally described based on the observation of specimens retrieved from the gill filaments of I. punctatus reared in a fish farm in Missouri, USA ( Minchew 1977). However, the species was not identified until Woodyard et al. (2022) provided a new and more complete molecular description based on specimens obtained from the same host in Mississippi, USA. Notably, morphology and molecular data for H. postexilis have been reported in China ( Zhang et al. 2023).

The morphology and measurements of the spores examined in this study ( Table 3) align with those reported by Minchew (1977), Woodyard et al. (2022), and Zhang et al. (2023) for H. postexilis . While the size of the plasmodia observed in this study surpasses prior records (see Table 3), this is probably due to the degree of maturation of the plasmodia. The plasmodia of our specimens contained many mature spores, whereas previously observed diminutive plasmodia were without mature spores ( Minchew 1977). Considering that our specimens were collected from small hosts during the summer, it is also possible that the variation in the plasmodium size is related to host development and/or seasonal factors. However, further comparison is unavailable since the previous reports lacked information concerning the collection date and host size ( Minchew 1977; Woodyard et al. 2022).

Additionally, the 18S rDNA sequence is consistent with previous findings ( Woodyard et al. 2022; Zhang et al. 2023), and consequently forms a clade with the other sequences of H. postexilis from USA and China in the phylogenetic tree ( Fig. 3 ). Both morphological and molecular analysis results indicated that all the newly collected specimens were H. postexilis , representing a novel country record for the species.

Figures

Fig. 1. Light photomicrograph of two fixed plasmodia with a gill filament of Ictalurus punctatus (A) and fresh myxospores (B–G) of Henneguya postexilis. Arrowheads indicate each plasmodium. B, D, E, Valvular view; C, F, G, sutural view. Scale bars: A, 200µm; B–G, 10µm.

Fig. 2. Line drawings (composite) of fresh myxospores of Henneguya postexilis. A, Valvular view; B, sutural view.Scale bars: 10µm.

Fig. 3. Maximum likelihood phylogenetic tree based on 18S rDNA data (1513bp including gaps) from Henneguya postexilis and other related myxozoans using Myxobolus lepomis as an outgroup. The accession number and scientific name of the newly sequenced species in this study are indicated in bold. The corresponding ISND accession numbers are shown. Arabic numerals at nodes indicate bootstrap values.