Academic journal article Estonian Journal of Ecology

New Data on the Helminths of the Muskrat (Ondatra Zibethicus) in Lithuania/ Uued Andmed Ondatra (Ondatra Zibethicus) Helmintidest Leedus

Academic journal article Estonian Journal of Ecology

New Data on the Helminths of the Muskrat (Ondatra Zibethicus) in Lithuania/ Uued Andmed Ondatra (Ondatra Zibethicus) Helmintidest Leedus

Article excerpt

INTRODUCTION

The muskrat (Ondatra zibethicus) is a semi-aquatic rodent belonging to the order Rodentia and family Cricetidae native to North America, but in the 20th century it was introduced to Europe and Asia from Canada. There were three centres of its spreading: the area of the present-day Czech Republic (from 1905), Finland (from 1916-1919), and France (from 1919) (Sokolov & Lavrov, 1993).

In 1951, 114 muskrats from Arkhangelsk were released into a tributary of the Nemunas River near the Curonian Lagoon (Slavsk District, Kaliningrad Region, Russia) (Lavrov, 1957) (Fig. 1). In 1954, 82 muskrats from Arkhangelsk were introduced into eastern Lithuania, and in 1956, 204 more were introduced from Kazakhstan to eastern and southern Lithuania. Since 1960 muskrats have been found in Silute District in the Nemunas delta. In 1964 they were first encountered in Vilkaviskis District (Prusaite et al., 1988).

The years 1967-1975 are considered a plentiful period (Prusaite et al., 1988); then there were about 40 000 muskrats in Lithuania. By today the number of muskrats has reduced. Now there are only 2000-2500 individuals in Lithuania (our unpublished data), the same number as in 1966 (Prusaite et al., 1988). Although muskrats are widespread, the density of these animals is different in various parts of Lithuania (Baleiauskas et al., 1999). The largest populations are in Utena, Moletai, Zarasai, Varena, Vilkaviskis, and Salcininkai districts. In the north of Lithuania the muskrat is rare.

[FIGURE 1 OMITTED]

From the parasitological aspect, the muskrat is an interesting object to study. It is fascinating to follow how its parasite fauna has changed after its acclimatization in Eurasia. During the acclimatization of the muskrat, new parasite species could have been introduced. The question arises what helminth species this mammal acquired in Eurasia. In the former USSR helminths of American origin were detected during parasitological studies of the muskrat (Lavrov, 1957).

In Lithuania the helminth fauna of the muskrat was studied in 1973-1976. A total of 222 muskrats from different localities of Lithuania were examined by the method of total helminthological dissection. Twenty species of trematodes, larvae of one species of cestodes, and one species of nematodes were found (Kiseliene & Mickus, 1976a, b; Kiseliene, 1983).

In later studies of five muskrats hunted in Silute District in 2001, six helminth species were detected (Mazeika et al., 2003). In that study the cestode Echinococcus multilocularis was found in rodents in Lithuania for the first time. The aim of the current study was to examine helminths of the muskrat from the Nemunas delta (Rusne Island) in Lithuania.

MATERIAL AND METHODS

The material for the investigation was collected on Rusne Island, Silute District, Lithuania (Fig. 1). Thirty-four muskrats, hunted in 2006-2007, were examined using the method of total helminthological dissection of individual organs. The intestines, stomach, and liver were examined. The content of the intestines and of the stomach was studied by the method of consistent flushing (Ivashkin et al., 1971). The helminths found were picked out and fixed in 70% ethanol. The helminths were coloured with acetic carmine and mounted in Canada balsam on slides or temporary water-glycerine preparations were made.

Helminthological terms were used according to the recommendations of Bush et al. (1997). The 95% confidence intervals for prevalence were calculated as described by Rojtman & Lobanov (1985). To estimate the parasite aggregation we used the simplest and most commonly used aggregation index: the ratio of the variance to the mean abundance ([S.sup.2]/A) (Poulin, 1998).

RESULTS

Of the 34 muskrats hunted in 2006-2007 21 or 61.8% were infected with helminths. In total eight helminth species were found (Table 1); four of them were found both in 2006 and 2007. …

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