Description of a new species of Myxobolus Butschli, 1882 from the Cirrhinus mrigala Hamilton, 1822 an edible fish of India

Abstract

Myxobolus Bütschli 1882 is an important group of parasitic protozoa infecting a large number of freshwater fish species worldwide. The severity of Myxobolus infection leads to heavy loss in production of fishes. During the survey of the fish parasites, a new species of the genus Myxobolus have been isolated from the gills of a freshwater edible fish Cirrhinus mrigala Hamilton, 1822 from Canning, South 24 Parganas, West Bengal, India which has been described here.

Introduction

Myxosporeans are considered to be one of the most abundant and diverse group of fish parasites found in different geographical areas (Landsberg and Lom 1991; Lom and Dykova 1992). Myxozoa Bütschli 1882, comprises more than one thousand two hundred available species commonly found in fish (Lom and Dykova 1992). Among them, the genus Myxobolus Bütschli 1882 is the largest group of the family Myxobolidae containing 744 described species (Eiras et al. 2005) and has been established as an important pathogen in fresh water fishes. About one hundred four species of this genus from Indian fishes have been reported in addition to 175 species belonging to the genera of Myxosporean (Kalavati and Nandi 2007). The genus Myxobolus was first recorded in 1882 by Butschli having spores with or without an iodinophilous vacuole and with one or two polar capsules. The Myxozoan spores having two polar capsules, with or without iodinophilus vacuoles and generally two sporogenic nuclei have been placed under the Genus Myxobolus Bütschli 1882 (Kudo 1933).

During the present study one species under the genus Myxobolus Bütschli 1882 has been identified. The species has been described here according to the guidelines of Lom and Arthur (1989) and Lom and Dykova (1992).

Materials and methods

Host fishes were collected from the bheries of Canning, South 24 Parganas, West Bengal, India and brought alive to the laboratory and cultured in the vats near the laboratory. Host fishes were examined time to time. The fishes were dissected and the gill smears were taken in the grease free slides (1 mm) and air dried. The slides were then fixed in methanol for 2–8 min. Then these slides were taken out and Giemsa stain was put on it. This Indian ink method of Lom and Vavrá (1963) was employed to identify the myxozoan spore and for permanent preparation. It was noticed that each slides were fully dipped into this stain. Staining was done for about 25–30 min and then washed in tap water. The slides were then covered with coverslips and mountant with DPX. The slides were then observed under microscope. Sporogonic plasmodia, when found, were carefully removed with sterile needles, smeared on clean grease free slides with drops of distilled water, covered with cover slips and sealed with DPX for examination of fresh spores under the oil immersion lens of Olympus KH phase contrast microscope. Some of the fresh smears were treated with various concentrations of KOH (2–10 %) for the extrusion of polar filament.

Some fresh smears containing the spore were treated with Lugol’s Iodine solution for the detection of iodinophilus vacuoles. Measurements based on twenty fresh spores (stained with both Lugol’s Iodine and Geimsa) were done with a calibrated ocular micrometer. All measurements are presented in micrometer (μm) as mean ± SD followed by parentheses by the range. Stained spores were examined under the oil immersion lens of Olympus KH phase contrast microscope. Photomicrographs of the stained spores were also taken with the help of an Olympus KH phase contrast microscope fitted with Olympus camera in 100X magnification.

Results and discussion

Myxobolus zoohuri sp. n. (Fig. 1a-d): Fig. 2a–c; Table 1)

Fig. 1.

a–d Photomicrographs of Myxobolus zoohuri sp. n. (Scale bar 5 μm)

Fig. 2.

a–c Camera lucida drawings of Myxobolus zoohuri sp. n. (Scale bar 5 μm)

Table 1.

Morphometric characters of M. zoohuri sp. n

Parameters	Range	Mean	Standard deviation (SD)	Standard error (SE)	Coefficient of variance (CV%)
Length of the spore (LS)	13.26–17.34	14.89	1.19	1.14	7.99
Breadth of the spore (BS)	4.99–7.03	6.32	0.53	0.73	8.39
Length of larger polar capsule (LLPC)	10.41–12.04	11.17	0.52	0.96	4.66
Breadth of larger polar capsule (BLPC)	2.24–3.16	2.83	0.28	0.46	9.85
Length of smaller polar capsule (LSPC)	10.1–11.22	10.63	0.42	0.94	3.94
Breadth of smaller polar capsule (BSPC)	2.04–3.06	2.71	0.36	0.42	13.27

Plasmodia

Plasmodia very small, microscopic, attached with the mucous membrane around gill lamellae. Colour creamy white, shape rounded (2–3 mm in diameter) and contains both late developmental stages and mature spores.

Spore description (measurements based on spores in frontal view)

Spore

Immature spores tear shaped. Two polar capsules pear shaped. Sporoplasm contains two nuclei. Mature spores tear shaped with dimension 14.89 ± 1.19 (13.26–17.34) × 6.32 ± 0.53 (4.99–7.03). Anterior end of the spores triangular and posterior ends blunt semicircular. The two polar capsules are unequal in shape. Larger polar capsules measures 11.17 ± 0.52 (10.41–12.04) × 2.83 ± 0.28 (2.24–3.16) and smaller polar capsules have the dimension of 10.63 ± 0.42 (10.1–11.22) 2.71 ± 0.36 (2.04–3.06). The capsules elongated with anterior tip and blunt posterior end. The polar filaments not extruded out. The polar capsules containing 17–18 coils in case of larger and 15–16 coils in case of smaller one. The granular sporoplasm fills the extra capsular region. It contains two sporoplasmic nuclei without any glycogen filled iodinophilus vacuole.

Spore index

• LS: BS = 1: 0.424

• LLPC: BLPC = 1: 0.253

• LSPC: BSPC = 1: 0.256

• LLPC: LSPC = 1: 0.951

• BLPC: BSPC = 1: 0.960

Taxonomic summery

Type host

Cirrhinus mrigala Hamilton.

Type locality

Canning, South 24 Parganas, West Bengal, India.

Type specimens

Slide No. MB/PA/KU/07-08 containing Holotype and four slides MB/PAKU/09-12 containing Paratype have been deposited in the collection of Prasitology Laboratory, Department of Zoology, University of Kalyani, Kalyani 741235, W.B.

Symbiotype

The host specimen bearing no. CM/PARA/01-07 deposited in the museum of the Parasoitology Laboratory, Department of Zoology, University of Kalyani, Kalyani 741235, W.B.

Site of infection

Gill lamellae.

Prevalence of infection

8 out of 21 hosts examined (38.095 %).

Specific epithet

The name of the species has been given after the name of Professor Moohanmmed Zohur Chisti, Emeritus Professor, University of Kashmir, Srinagar, India for his outstanding contribution in the field of Parasitology.

Discussion

Taxonomic affinities

The Myxozoan parasite under discussion having two polar capsules, with or without iodinophilus vacuoles and generally two sporogenic nuclei justifies its inclusion under the family Myxobolidae and genus Myxobolus Bütschli 1882 as described by Kudo (1933).

The present species resembles a number of Myxobolus species in morphology or morphometry of the spores and polar capsules. These species includes M. karnatakae Hagargi and Amoji 1981; M. mahendrae Sarkar 1986; M. variformis Haldar et al. 1996; M. orissae Haldar et al. 1996; M. rocatlae Basu and Haldar 2002; M. catmrigalae Basu and Haldar 2004. A comparative statement has been incorporated in Table 2.

Table 2.

Comparative morphology of M. zoohuri sp. n. with other related species

Name of the species	Host	Site of infection	Length of spore	Breadth of spore	Length of larger polar capsule	Breadth of larger polar capsule	Length of smaller polar capsule	Breadth of smaller polar capsule	Polar filament	Filamentous coils (FC)
M. catmrigalae Basu and Haldar (2004)	Catla catla Ham. × Cirrhinus mrigala Ham. (Hybrid)	Gill lamellae	20.4	16.3	11.9	2.3	11	2.3	Absent	Larger: 20–25 Smaller: 20–23
M. karnatakae (Hagargi and Amoji 1981) Landsberg and Lom (1991) [Syn. Myxosoma Kare Hagargi and Amoji (1981)]	Barbus chola Ham. and Buch.	Caudal muscles	16.30–19.40 (17.58)	10.88–13.60 (11.1)	10.88	5.44	7.3	3.58	Absent	6–7
M. mahendrae Sarkar (1986)	Catla catla Ham.	Gill arch epithelium, bucco-pharyngeal cavity	11.52–13.96 (12.7)	9.77–10.47 (9.2)	6.28–7.33 (6.98)	3.49–4.19 (3.73)	4.19–6.98 (5.44)	3.14–3.49 (3.42)	Absent	Large: 6–7 Small: 4–5
M. orissae Haldar et al. (1996)	Cirrhinus mrigala Ham.	Gills	13.0–19.5 (15.71)	4.9–8.1 (6.8)	7.3–11.8 (8.8)	2.4–3.2 (1.78)	6.5–11.4 (7.58)	1.6–3.4 (2.57)	Absent	_
M. rocatlae Basu and Haldar (2002)	Catla catla Ham. × Labeo rohita Ham. (Hybrid)	Gills, guts	17.5–19.3 (18.5)	5.6–6.2 (5.9)	11.8–13.7 (12.9)	2.5–3.0 (2.85)	10.0–12.2 (11.3)	2.0–2.4 (2.2)	Absent	Larger: 17–19 Smaller: 15–18
M. variformis (Haldar et al. 1996) Kalavati and Nandi (2007) [Syn. Myxobolus variabilis Haldar et al. (1996)]	Mystus gulio Ham.	Body muscles, gills	13.0–17.9 (15.2)	4.9–8.1 (5.65)	8.1–11.7 (9.67)	1.6–4.0 (2.84)	6.5–11.4 (8.6)	1.6–3.2 (2.4)	_	_
Myxobolus n. sp. present study	Cirrhinus mrigala Ham.	Gill lamellae	13.26–17.34 (14.89)	4.99–7.03 (6.32)	10.41–12.04 (11.17)	2.24–3.16 (2.83)	10.1–11.22 (10.63)	2.04–3.06 (2.71)	Absent	Larger: 17–18 Smaller: 15–16

The present species is larger in comparison to M. mahendrae while it is smaller than M. catmrigalae, M. rocatlae, M. karnatakae and M. orissae respectively in relation to its length. Whereas, M. catmrigalae, M. karnatakae and M. orissae are larger in relation to both its length and width of the spore than the present species but in M. rocatlae and M. variformis the length of the spore is much longer than the present form while the breadth is slightly smaller in size. The length of large polar capsule is bigger in case of only M. rocatlae while it is smaller in all the compared species along with the present form. Where as the width is larger in M. karnatakae and M. mahendrae but resembles closely with M. catmrigalae, M. rocatlae and M. variformis respectively. Furthermore, while comparing the length and breadth of smaller polar capsule it is found that the length is larger only in M. rocatlae and M. catmrigalae while it is smaller in case of other compared species and breadth is larger in M. karnatakae, M. mahendrae and smaller in rest of the species. M. catmrigalae and M. rocatlae possesses larger polar capsule in comparison to M. karnatakae, M. orissae, which possesses smaller polar capsule in comparison to present form. The shape of the spore also varies. It is oval and somewhat elongated in shape in all the compared species where as it is tear shaped in the present form. Polar filament is absent in all the forms but the species differs from each other in respect to the number of filamentous coil. The highest number of filamentous coil has been observed in M. catmrigalae in comparison to other forms while M. rocatlae resembles the present species under study having comparatively same number of coils.

The size of the spore of the present form resembles closely to M. variformis, in respect to its length and morphometry but the polar capsules are smaller than that of present one. Although in some cases M. variformis shows equal sized polar capsules along polar filaments. Furthermore, in M. rocatlae the surface of the spore along with the length and breadth of larger and smaller polar capsule is much bigger in comparison to present form.

Considering all these points, the present Myxobolus species under description is new to science and hence it is designated as Myxobolus zoohuri sp. n.

Abbreviations

LS

Length of the spore

BS

Breadth of the spore

LLPC

Length of the larger polar capsule

BLPC

Breadth of the larger polar capsule

LSPC

Length of the smaller polar capsule

BLPC

Breadth of the smaller polar capsule

PC

Polar filament

FC

Filament coil