Thelohanellus caudatus infection

Sz, Csaba, ekely, Ghosh, Subarna, Borz, eka, ak, Goswami, Urvashi, alm, Moln, an, ar & Cech, abor, 2021, The occurrence of known Myxobolus and Thelohanellus species (Myxozoa, Myxosporea) from Indian major carps with the description of Myxobolus bandyopadhyayi n. sp. in West Bengal, International Journal for Parasitology: Parasites and Wildlife 16, pp. 18-25 : 19-21

3.1. Thelohanellus caudatus infection of rohu ( Figs. 2–4 )

Thelohanellus infection on the fins was found in 4 rohu specimens from 13 fish obtained from the Diara fish farm, while 3 infected specimens were observed among the 12 fish purchased on the fish market. Plasmodia (1–14 cysts) were recovered from the tail fins and the anal fins. Relatively small plasmodia of elliptical shape ( Fig. 2 ), 1–2 mm long and 0.5–1 mm thick, locating at the proximal parts of the fins, close to the body, attached to the cartilaginous fin rays.

Mature spore ( Figs. 3 and 4 ) pyriform, with slightly tapering anterior and round posterior end, 13.7 ± 0.93 (13.3–14.6) long (n = 25), 9 ± 0.82 (7.5–9) wide (n = 25) and 6.8 ± 0.41 (6.2–7.3) thick (n = 15). The wall relatively thick 1 ± 0.2 (0.7–1.1). Single short ellipsoidal polar capsule present close to apex of spore, 6.5 ± 0.4 (6.2–6.9) (n = 25) long, 4.7 ± 0.47 (4.2–5) (n = 25) thick. Polar tubules not seen. At one side between the polar capsule and the sporoplasm a bright nucleus of the capsulogenic cell, about 1 × 1.5 present. No iodinophilous vacuole or mucous envelope seen.

Host: Rohu, Labeo rohita Hamilton.

Locality: Diara Fish Farm (Hooghly District) fish pond and hatchery (22 ◦ 28 ′ 31 ′′ N 88 ◦ 09 ′ 54 ′′ E) and fish market Naihati, Battala market (22.89 ◦ N 88.42 ◦ E) (on the Kalyani expressway)

Site of infection: Fins.

Material: Photo-types were deposited in the parasitological collection of the Zoological Department, Hungarian Natural History Museum, Budapest, Coll. No. HNHM-PAR-72077. The ssrDNA sequence of T. caudatus was deposited in the GenBank under accession numbers MZ 230375, MZ 230376 and MZ 230379.

Prevalence of infection: 7 specimens from 25 fish.

Molecular data: ssrDNA sequences of T. caudatus ( MZ 230375-6 and MZ 230379) collected from the fins of rohu were identical with each other and showed a 99.8% similarity with the T. caudatus sample deposited in the GenBank as KM 252684. However, with the other

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deposited sequences ( MK 412941) only 98.8% similarity was found. Interestingly enough, a 99.0% similarity was also obtained with sequence ( KM 252683) of T. habibpuri Acharia and Dutta (2007) . Interestingly, there is also another T. caudatus clade (KC865607, KF583877, KJ 476877) with a maximum bootstrap distinct from the above-mentioned sequences. Genetic similarities of our samples are 87.3% in the case of two sequences (KF583877, KJ 476877) and 71.1% in the case of KC865607.

Remarks: Based on the similarity in morphology and size of the present species and the one described by Pagarkar and Das (1993), we regard the species found by us as T. caudatus . The identification is strongly supported by the similarity between the sequences reported by Mondal et al. (2014) and those presented in this study. According to the morphological similarity of T. caudatus and T. avijity Basu and Haldar ,

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2003, we regard the latter species as a synonym of T. caudatus . Likewise, Thelohanellus habibpuri Acharia and Dutta (2007) is considered also a junior synonym of T. caudatus . Acharia and Dutta (2007) described T. habibpuri from the fins of rohu and studied its ultrastructure, but provided only an incomplete morphological description. The spore morphology and measurements given for M. habibpuri correspond to those of T. caudatus sp. ( Table 1).

3.2. Description of Myxobolus bandyopadhyayi n. sp. ( Figs. 5–7 )

Round-shaped plasmodia ( Fig. 5 ) with a diameter of 700 to 1,500 were located in the superficial tissues of the scale. They occurred in 3 out of the 12 rohu specimens from the fish market. Plasmodia contained 4,000 to 10,000 spores.

Myxospores ( Figs. 6 and 7 ) small sized, roundish or short ellipsoidal in frontal view and lemon shaped in sutural view. Spores 8.4 ± 0.19 (8.3–8.8) long, 6.6 ± 0.54 (5.2–7.5) wide and 4.6 ± 0.4 (4.3–5.4) thick. Two polar capsules short pyriform, different in size. The larger 4.2 ± 0.38 (3.7–4.5) long and 2.5 ± 0.18 (2.2–2.7) wide, the smaller 2.3 ± 0.4 (1.7–2.8) long and 1.65 ± 0.05 (1.6–1.7) wide. Polar tubules not seen. Spore with approximately 1.2 long, triangular, eccentrically located intercapsular appendix. Sporoplasm nuclei indiscernible. A small distinct iodinophilous vacuole present in the sporoplasm. Mucous envelope not found. The thickness of the spore wall 0.65 ± 0.05 (0.6–0.7). Nuclei of the polar capsules distinct.

Type host: Rohu Labeo rohita Hamilton.

Type locality: Naihati, Battala market (22.89 ◦ N 88.42 ◦ E) (on the Kalyani expressway)

Site of development: Scale.

Type material: Photo-types and histological preparations were deposited in the parasitological collection of the Zoological Department, Hungarian Natural History Museum, Budapest, Coll. No. HNHM-PAR-72078. The ssrDNA sequence of M. bandyopadhyayi was deposited in the GenBank under accession number MZ230380 .

Prevalence of infection: 3 specimens from 12 fish.

Molecular data: ssrDNA sequences of M. bandyopadhyayi ( MZ 230380) collected from the scales of rohu significantly differed from any myxosporean species deposited in the GenBank. This species was located as a single species in a distinct clade, the highest similarity to other myxosporean species was 83.9% in relation to Myxobolus chakravartyi .

Remarks: By the short oval shape of its spores, by the different sized but short ellipsoidal polar capsules, this species differed from most species known from major Indian carps. Of the Myxobolus species with two different-sized polar capsules M. buccoroofus Basu and Haldar, 2004 had dissimilar spore shape. Polar capsules of M. calbasui Chakravarty, 1939 , M. chilkensis Kalavati et al., 1992 and M. bhadrensis Seenappa and Manohar, 1980 had elongated shape. Spores of M. edellae Sarkar, 1999 are also nearly spherical, but the difference between its two polar capsules is only moderate.

Etymology: The species is named after Prof. Probir K. Bandyopadhyay, the well-known fish parasitologist, who managed this recent co-operation from the Indian side and worked actively until his decease in January 2021.

Figures

Fig. 2. A plasmodium (P) of Thelohanellus caudatus in the fin of a rohu in close contact with the cartilaginous fin ray (Fr). Mount picture. Bar = 200 μm.

Fig. 3. Spores of T. caudatus. Mount picture. Bar = 10 μm.

Fig. 4. Schematic drawing of spore of T. caudatus, a: frontal view, b: sutural view. Bar = 10 μm.

Fig. 5. Myxobolus bandyopadhyayi n. sp. plasmodium (P) in the scale of a rohu. Mount picture. Bar = 2 mm.

Fig. 6. M. bandyopadhyayi n. sp. spores of a rohu in frontal view. Inset: A spore in sutural view. Mount picture. Bar = 10 μm.

Fig. 7. Schematic drawing of spore of M. bandyopadhyayi, a: frontal view, b: sutural view. Bar = 10 μm.