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Protistology 9 (2), 67-74 (2015) Protistology
Prevalence of Myxidium rhodei (Cnidaria, Myxosporea) in the Lake Baikal basin*
Marina Batueva1
Nikolay Pronin1 and Svetlana Pronina2
1 Laboratory of Parasitology and Ecology of Hydrobionts, Institute of General and Experimental Biology of Siberian Branch of Russian Science Academy, Ulan-Ude, Russia
2 Faculty of Medicine, Buryat State University, Ulan-Ude, Russia
Summary
Distribution and prevalence of a myxosporean parasite, Myxidium rhodei Leger, 1905, infecting two cyprinid fish, a roach Rutilus rutilus and Siberian dace Leuciscus leuciscus baikalensis, have been studied in water bodies of the Lake Baikal basin. Over 15-year period (1998-2013), a total of 246 roaches and 189 daces from 27 stations were surveyed. Plasmodia of M. rhodei were registered in the Bowman's capsules and interstitials in fish kidneys. M. rhodei was recorded in roach and dace almost in all studied water bodies and rivers of the Lake Baikal basin, except Lake Ugii-Nur and the northern part of Lake Khovsgol. Infection intensity of roaches was significantly higher in Lake Baikal than in rivers and lakes of the basin. Benthophagous roaches displayed significantly higher infection intensity than euryphagous daces.
Key words: distribution, fish, Lake Baikal, Myxidium, Myxosporea, parasites
Introduction
According to the estimates (Pugachev and Podlipaev, 2007; Eiras et al., 2011), the genus Myxidium Butschli, 1882 includes from 110 to 232 species. Myxidium rhodei Léger, 1905 is one of the most common parasites in cyprinids of the Palaearctic region (Shulman, 1966). The majority of investigations have been devoted to distribution,
* The Editorial Board appreciates the valuable input of the Referee (Y.S.) whose advices significantly improve the quality of article and greatly contributed to its preparation for publication.
biology and ecology of M. rhodei in Europe (Shulman, 1966; Kepr, 1987; Dykova et al., 1987; Athanassopoulou and Sommerville, 1993; Alvarez-Pellitero, 1989; Brummer-Korvenkontio et al., 1991; Saraiva et al., 2000; Dzika et al., 2006).
M. rhodei was registered for the first time within the Lake Baikal basin in 1961 in a crucian carp from Lake Karas of the Ivano-Arakhley lake group (Pronin, 1975) and later in Chivyrkuy Bay of Lake Baikal (1981-1990) (Tarmakhanov, 1991). Since 1998, comprehensive studies ofM. rhodei have been performed in the Lake Baikal basin (Badmaeva et al., 2005; Pronin et al., 2010). M. rhodei was the dominant species in the roach infracommunities of all age groups in Chivirkuy Bay and Selenga River
© 2015 The Author(s)
Protistology © 2015 Protozoological Society Affiliated with RAS
Delta (Dugarov et al., 2011). This paper presents the data on spatial distribution of M. rhodei in two major hosts, fish of the family Cyprinidae: a roach Rutilus rutilus and Siberian dace Leuciscus leuciscus baicalensis inhabiting Lake Baikal basin. These species are widespread and have commercial importance in the Lake Baikal basin.
Material and methods
Samples for studying spatial distribution of M. rhodei were collected in the gulfs of Chivyrkuy Bay (Fig. 1), the second largest bay (300 km2) after Barguzin Bay, from different depths ranging from the shallow eutrophic area in the south (2—4 m), mean-depth mesotrophic area (5—10 m) to the oligotrophic area in the north (up to 100 m) (Pronin, 2000). Sampling was also performed in shallow gulfs ofthe coastal sand bars (sors) of Lake Baikal: Posolsk Sor (area, S 35 km2), Cherkalov Gulf (S 25 km2), Proval Gulf (S 185 km2), and in the southern part of the Selenga River shoal. The samples were collected from the Selenga River (length, L 1024 km) and its tributaries: channels of Kharauz and Galuta, and near the settlement of Murzino; from the Selenga River near the city of Ulan-Ude, upstream of the Khujir River; near the settlement of Zuunburen, as well as from Lake Gusinoye (S 164.7 km2) and Lake Khovsgol (S 2,620 km2) and its tributary, the Eg River (L 475 km). Fishes were sampled from the following locations along the Orkhon River (L 1,124 km), the main tributary ofthe Selenga River: near the settlement of Orkhon, near the city of Sukhbaatar, from the Ero River (L 323 km), a right tributary of the Orkhon River, and from Lake Ugii (S 25 km2). The roaches were examined from the Barguzin River (L 480 km), the second largest tributary of Lake Baikal, near the settlement of Kurumkan. In Pribaikalye (Fig. 1), samples were collected from Lakes Arangatuy (S 55 km2) and Kotokel (S 70 km2). Stationary investigations were performed at the Ecohydrobiological Station "Monakhovo" of the Institute of General Ecology and Biology SB RAS located in Chivyrkuy Bay.
Overall, 246 roaches (5 to 7 yrs old) and 189 Siberian daces (5 to 7 yrs old) were examined (Table 1).
To assess distribution of myxosporidia among fish, two parameters were estimated: prevalence of infection, equal to percentage of the infected fish and infection intensity measured as the number of plasmodia per fish (Bush et al., 1997).
To determine the infection intensity, kidneys were squeezed between two glasses and examined
in a stereomicroscope Stemi Carl Zeiss. They were fixed in 10% formalin or Bouin's solution. Paraffin sections (5—6 ^m) were stained with hematoxylin-eosin and azure-eosin. Histological analysis of kidney tissues and spore morphology were performed with a light microscope Axio Imager M.2 Carl Zeiss. Statistical data were treated with Kruskal-Wallis test (H-test). A package "Statistica, ver. 8, StatSoft Russia" was used for multiple comparisons, also known as a posteriori tests (post-hoc) for non-parametric data. The 95% confidence intervals for prevalence were calculated as described by Rojtman and Lobanov (1985). Differences in intensity of M. rhodei infection of roach and dace among localities were demonstrated by box plots.
Results
Morphology and tissue tropism of the parasite
Spores of Myxidium rhodei were either fusiform, or crescent-form, or spiral S-shaped, with somewhat pointed ends. Each valve displayed longitudinal ridges. Spores contained pear-shaped polar capsules, with polar filaments forming 4 to 5 coils inside (Figs 2, 3).
Amoeboid embryo was located between the polar capsules. The middle part of the spore was narrowed, and the spore ends were pointed (Fig. 2). In Bowman's capsules M. rhodei plasmodia with pseudopodia were registered from April to June (Fig. 4, a-b). When the level of infection was low, plasmodia were recorded only in Bowman's capsules (Fig. 4, a-c). A visceral layer ofthe Bowman's capsule and mesangium ofthe renal corpuscle atrophied with the development ofplasmodium, whereas a parietal layer was preserved, thus protecting the parasite from the attack of immune cells and further development of granulomatous inflammatory reaction.
M. rhodei plasmodia that penetrated interstitials were surrounded by a thick macrophage capsule (153.6 ± 2.67 ^m in diameter) (Fig. 4, d).
Distribution
M. rhodei was recorded in roach and dace almost in all examined water bodies and rivers of the Lake Baikal basin, except Lake Ugii-Nur and the northern part of Lake Khovsgol (Table 1). Maximal M. rhodei prevalence (100%) was registered in the roach populations from Lake Arangatuy and the coastal-sor area of Lake Baikal (Chivyrkuy Bay, Proval Bay, Cherkalov Sor, and Posolsk Sor), as well
100° 56° 104° 108° 112° 54°
100° 46° 108°
Fig. 1. Map of sample sites of the studies performed in 2000-2013. 1 — Lake Arangatuy; 2 — Chvirkuy Gulf, Monakhovo Bay; 3 — Chivirkuy Gulf, Onkogon Bay; 4 —Barguzin River; 5 — Lake Kotokel; 6 — Proval Bay; 7 — Selenga Delta, Galuta tributary; 8 — Cherkalov Bay; 9 — Posokskiy Bay; 10 — Selenga Delta, near settlement ofMurzino; 11 — Selenga River, near the settlement of Zenith; 12 — Selenga River, near the city of Ulan-Ude; 13 — Lake Gusinoye, discharge of warm water from thermal electric station; 14 — Lake Gusiniye, near the settlement of Baraty; 15 — Orkhon River, near the city of Sukhbaatar; 16 — Selenga River, near the settlement of Zuunburen; 17 — Ero River; 18 — near the Khujir River; 19 — Orkhon River, near the city of Orkhon; 20 — Eg River; 21 — south part of Khovsgol Lake; 22 — nothern part of Khovsgol Lake; 23 — Ugii Nuur.
as at several stations of the Selenga River and in the Barguzin River. The infection prevalence in roach was significantly lower in Lake Khovsgol (42.8%), Gusinoye (26%) and Kotokel (47%). The M. rhodei prevalence among dace populations varied from 33, 3 % (the Orkhon River near the city of Sukhbaatar) to 93% (the Orkhon River near the settlement of Orkhon) (Table 1).
The comparison of data on infection intensity using the Kruskal-Wallis test showed significant differences (H=322. 07; N=649; df=26; p=0.000) between samples of roach and dace at 27 stations. The subsequent (post-hoc) pairwise comparison of the M. rhodei infection intensity in roach and dace revealed significant differences between the stations belonging to the coastal-sor zone of Lake Baikal,
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Table 1. Prevalence and infection intensity of Myxidium rhodei in Rutilus rutilus and Leuciscus leuciscus baicatensis at the sampling sites.
Region № Locality Year Prevalence (°/o) Intensity Year Prevalence (°/o) Intensity
range average range average
Roach Dace
Lake Baikal, Chivirkuy Gulf 1 Lake Arangatuy 2000 100 91- 6800 2538.45 - -
2 Monakhovo Bay 2000 100 2-3227 1149.04
3 Onkogon Bay 2001 100 24-638 246.3 2001 36,6 1-164 12,2
Barguzin River 4 Near the settlement of Kurumkan 1999 100 50-127 82.33 -
5 Kotokelskoye Lake 2009 47.0 1-401 48.25 -
Lake Baikal 6 Proval Bay 2000 100 7-1070 178.93 - - - -
Selenga Delta 7 Galuta tributary 2001 100 13-1825 334.2 - - -
Lake Baikal 8 Cherkalov Bay 2003 100 53-1350 543.9 2003 80 8-58 21,93
9 Posolskiy Bay 2003 100 14-3360 480.2 - - -
Selenga Delta 10 Near settlement of Murzino 2001 100 50-467 78.4 2001 71,4 2-141 20,43
Selenge River 11 Near the settlement of Zenith 2005 53,8 2-185 48
12 Near the city of Ulan-Ude 1998 37.5 1-393 28.31 -
Gusinoye Lake 13 Discharge of warm water from Thermal electric station 2013 26.66 2-127 14.46 - - -
14 near the settlement of Baraty 2013 57.14 3-36 9.5 - - -
Orkhon River 15 Near the city of Siikhbaatar 2013 66.7 5-150 49.5 2013 33,3 1-79 33,3
Selenga River 16 Near the settlement of Zuunburen 2013 73.33 14-1560 310.4 2013 86,7 5-1500 166,53
Orkhon River 17 Ero River - - - - 2005 89,47 1-309 119,31
Selenga River 18 Upstream of the Khujir River 2013 100 11-650 136.66 - " - -
Orkhon River 19 Near the settlement of Orkhon - - - - 2013 93,3 1-108 23,2
20 Eg River - - - - 2005 73,9 1-393 69,17
Khovsgol Lake 21 South part 2005 42.8 2-6 1.71 - - -
22 Nothern part 2011 0 0 0 - - - -
23 Ugii Nuur 2005, 2013 0 0 0 - - -
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Fig. 2. Spores M. rhodei from the kidney. Scale Fig. 3. Schematic illustration of M. rhodei spores.
bar: 10 ^m. A, B — frontal view; C — sutural view. Scale bar: 10 ^m.
rivers and lakes of the Baikal basin. The infection intensity in roach varied from the maximal (over 6,000 cysts) in Lake Arangatuy to high (more than 3,000 cysts) in Monakhovo Gulf of Chivyrkuy Bay, and the lowest in Lake Khovsgol (1-6 cysts). Significant differences were observed in Lake Baikal (p=0.00) but not the lakes and rivers (p=0.49). The infection intensity in dace varied greatly (51,500 cysts) in fish from the Selenga River (near the settlement Zuunburen) or insignificantly (1-79 cysts) in dace from the Orkhon River near the city of Sukhbaatar. The differences in infection intensity of dace among Lake Baikal and rivers stations were significant (p=0.04), among Lake Baikal and lakes of the basin were insignificant (p=0.23). The significant differences in infection intensity between two hosts were observed for the populations of roach and dace from Lake Baikal (p=0.00), from lakes (p= 0.00), and from rivers (p=0.01) (Fig. 5).
Discussion
The studies presented showed that Bowman's capsules were the main M. rhodei infection in roach and dace kidneys, whereas kidney interstitials were infected only occasionally. This is consistent with the data of other researchers on tissue tropism of M. rhodei in roach Rutilus rutilus, chub Leuciscus cephalus, bream Abramis brama, and undermouth Chondrostoma polylepis from other areas (Shulman, 1966; Dykova et al., 1987; Alvarez-Pellitero, 1989; Saraiva et al., 2000; Longshaw et al., 2005). M. rhodei induced immune response of the host when it was localized in the interstitial.
The higher prevalence and infection intensity of roach-benthophage comparatively to dace-euryphage (Fig. 5) suggest that the roach is a
dominant obligate host of M. rhodei in Lake Baikal, whilst the dace is a subdominant one.
M. rhodei infection intensity in the local roach populations within Chivyrkuy Bay was significantly higher in its eutrophic part (Monakhovo Gulf) than in the oligotrophic area (Onkogon Gulf). Outside Lake Baikal, we observed opposite relations between the trophic level of the water body and intensity of infection: minimal prevalence and intensity of infection in roach populations was observed in eutrophic Lake Arangatuy, it increased in mesotrophic Lake Gusinoye and reached maximum in oligotrophic Lake Khovsgol. In Finland and Poland, a positive bond between prevalence/intensity of M. rhodei infection in roach and the trophic level of the water body was recorded: in the oligotrophic Lake Vatia (Finland) the infection intensity was lower (65%) than in eutrophic Lake Saravesi (79%) (Brummer-Korvenkontio et al., 1991). High level of M. rhodei infection in fish inhabiting eutrophic lakes can be explained by abundance of oligochaetes, the definitive hosts of myxosporea. The absence of M. rhodei in roach from Lake Ugii Nuur is likely to be a consequence of considerable annual changes in the water level, species composition of zoobenthos and ichthyofauna, and anthropogenic pollution (Dgebuadze et al., 2009). The importance of the latter factor corroborates with low infection intensity (4.4%) recorded in roach populations inhabiting highly polluted Lake Wulpicskie in Poland (Dzika et al., 2006).
Acknowledgements
The work was supported by the basic project SB RAS (No. VI.51.1.3) and RFBR grant 14-04-91176 GFEN_a. The authors are thankful to the colleagues
Fig. 4. Histological sections of the kidney of Rutilus rutilus. a — Plasmodia of M. rhodei developing within hypertrophied Bowman's capsules, H&E; b — Bowman's space of a renal corpuscle almost filled with a plasmodia, H&E; c — plasmodia of M. rhodei with mature spores, surrounded by connective tissue capsule, H&E; d — inflammatory reaction provoked in the renal interstitial by an early stage of a plasmodia, H&E.
from Laboratory of Parasitology, Institute of General and Experimental Biology SB RAS for their assistance in joint field works. They also express many thanks to P. Gunin and Yu. Dgebuadze, leaders of the Joint Russian-Mongolian Integrated Biological Expedition, for organization and support of studies performed in the Selenga River basin on the Mongolian territory.
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Address for correspondence: Marina D. Batueva. Laboratory of Parasitology and Ecology of Hydrobionths, Institute of General and Experimental Biology of Siberian Branch of Russian Science Academy, Sakhya-nova street 6, Ulan-Ude, 670047, Russia; e-mail: badmm_@rambler.ru
