INTRODUCTION

Chinese sleeper Perccottus glenii Dybowski, 1877 is an alien species of the Far Eastern ray-finned fish introduced into the reservoirs of Europe and Siberia. The neighborhood of St. Petersburg is chronologically the point of the primary introduction of the Chinese sleeper. In 1916, specimens were released from an aquarium into one of the suburban garden ponds [6]. Now this species is found in many water bodies of St. Petersburg and Leningrad oblast, including the desalinated eastern part of the Gulf of Finland [2, 8, 11]. It was first discovered in the early 1950s in the littoral part of the Gulf of Finland [6].

Large-scale parasitological studies of the Chinese sleeper were carried out in 2008–2015 [26]. Nevertheless, some new territories of the expanded range of this fish species, including the northwest of Eastern Europe, have not yet been covered by these studies.

This study aims to describe the parasitic fauna of the invader Perccottus glenii in the reservoirs of St. Petersburg and its environs (Russia).

MATERIALS AND METHODS

The Chinese sleeper was caught in the reservoirs of St. Petersburg and its environs: the artificial ponds of Aviator Park (59°52ʹ N, 30°18ʹ E) and Sosnovka Park (60°10ʹ N, 30°21ʹ E), the dammed Zybin Brook (59°58ʹ N, 30°28ʹ E), and the desalinated water area of the eastern part of the Gulf of Finland. Five specimens were examined from the pond in Aviator Park (total length of body (L) 105–175 mm, June 2015), one specimen from the pond of Sosnovka Park (L = 91 mm, June 2015), and four specimens from the Zybin Brook (L = 115–160 mm, June 2015). In the Gulf of Finland, the Chinese sleeper was caught in the coastal area of Kotlin Island (60°10ʹ N, 29°43ʹ E) and in the water area free from thickets near the city of Sestroretsk (60°5ʹ N, 29°54ʹ E). Fourteen specimens were examined from the area of Kotlin Island (L = 62–156 mm, May 2016) and two specimens from the area nearby Sestroretsk (L = 220–250 mm, June 2015). Freshly caught specimens were examined. Fixation and subsequent treatment of parasites were carried out by standard methods [5]. To identify the parasites, the taxonomical keys [3, 4, 17, 18, 21] and research data [1, 7, 9, 12, 20, 22] were used. Two indicators of host contamination were used: the prevalence expressed in terms of the number of infected fish (for all groups of parasites) and the intensity of infection (the number of parasite individuals found in the host) for macroparasites only.

RESULTS AND DISCUSSION

Twenty-seven parasite species/taxa have been found in the studied fish (Table 1). Specific parasites for this host were represented by one species only, Goussia obstinata Sokolov et Moshu, 2014. The species composition of parasites of the individuals caught in the park ponds and the dammed Zybin Brook was extremely poor; most of the parasite species were presented in the fish sampled in the Gulf of Finland. The larvae and juveniles of the imaginal phase of development prevailed among the macroparasites recorded in the Chinese sleeper of this reservoir, both in number of species and in number of individuals (Table 1). Sexually mature specimens of macroparasites have been registered only in the largest fish.

Table 1.   Parasites and indices of infestation of the Chinese sleeper in the studied reservoirs of St. Petersburg and its environs
Full size table

The Gulf of Finland, as a very large natural body of water with a rich parasitofauna, has a considerable potential for this fish species in regard to being a host for parasites. However, in the studied Chinese sleeper individuals, this potential was realized only for a part of species/taxa: for all protists, glochidia, metacercariae, and nematode juveniles with tissue localization, as well as, possibly, for plerocercoid of Eubothrium rugosum (Batsch, 1786). The Chinese sleeper is an undoubted eliminator for Acanthocephalus ranae (Schrank, 1788). Tailless amphibians are the obligatory final hosts of A. ranae [18]. In the vicinity of St. Petersburg, the coastal zone of the Gulf of Finland is inhabited by at least one of the species of these vertebrates, Pelophylax ridibundus (Pallas, 1771) [10]. For many intestinal helminths (juveniles of Bucephalidae, Lissorchiidae, and Opecoelidae families of trematodes, as well as juveniles of Camallanus), the degree of suitability of the Chinese sleeper as a host is unclear. The facts of registration of adult worms Sphaerostoma spp., Camallanus spp., and Bunodera luciopercae (Müller, 1776) in some specimens of the Chinese sleeper are unlikely to clarify this issue (Table 1). It is known [2, 23] that large individuals of the Chinese sleeper in the eastern part of the Gulf of Finland feed mainly on fish, and these parasites could pass to them from the swallowed fish. It should be noted that, in a number of other European water bodies, Camallanus sp., Bucephalus polymorphus Baer, 1827, Sphaerostoma globiporum (Rudolphi, 1802), and Parasymphylodora markewitschi (Kulakowskaya, 1947) have been registered in the Chinese sleeper; all of these parasite species were represented by juvenile individuals (larvae and young marites) [13, 26]. The plerocercoid Diphyllobothrium vogeli Kuhlow, 1953 was found in the intestine of one individual, where it passed undoubtedly from a three-spined stickleback Gasterosteus aculeatus Linnaeus, 1758 that it had swallowed; the last is the obligate second intermediate host of this cestode species (its remains were present in the intestines of the Chinese sleeper). Among the parasites recorded in the Chinese sleeper in the Gulf of Finland, there were no species reliably attributed to the marine fauna. It is noteworthy that there were no Chinese sleeper-specific parasites with a heteroxenous life cycle found in the reservoirs of St. Petersburg and its environs; this agrees with the origin of local populations of this fish species from the aquarium individuals [24, 25].

Chronologically, the second point of introduction of the Chinese sleeper (in 1950), associated with the release of individuals from aquaria, refers to the upper part of the Moscow River basin [19, 28]. In comparison with that population [15, 25, 26], fewer species/taxa of parasitic ciliates (5 versus 10), in particular, of ectoparasitic infusorians (3 versus 7), but more metazoan parasites (22 versus 11), have been recorded in the Chinese sleeper from the water bodies of St. Petersburg and its environs (Table 1). In this case, all types of parasite–host relations (from obligate to captive) in the Chinese sleeper were taken into account. These differences in the number of species/taxa of metazoan parasites are regular. The species richness of the parasites of the introduced Chinese sleeper is largely due to the diversity of the fish in the recipient reservoir [13]. The qualitative and quantitative composition of the freshwater and euryhaline fish in the eastern part of the Gulf of Finland [19] is richer than that of all the surveyed reservoirs near Moscow (the Neverovo sand-pit, Glubokoe Lake, etc.) [14, 15]. Differences in the species composition of the ectoparasitic ciliates are apparently random. The Chinese sleeper from the Gulf of Finland and from the ponds of St. Petersburg was infested by them poorly (Table 1), which depleted their species composition. Accordingly, in order to obtain representative data on the species richness of the ciliates parasitizing on the Chinese sleeper in the Gulf of Finland and in the city ponds of St. Petersburg, additional studies are needed.

CONCLUSIONS

Twenty-seven species/taxa of parasites have been registered in the Chinese sleeper sampled in the first chronological point of the primary introduction; one of these parasite species (Goussia obstinata) is species-specific for this host. The species composition of parasites is consistent with the origin of the local populations of this fish species from the aquaria individuals. The maximum species richness of parasites (26 species/taxa) is found in the Chinese sleeper sampled in the desalinated water area of the eastern part of the Gulf of Finland. The suitability of the Chinese sleeper as a host is unequal for all parasites found.

ACKNOWLEDGMENTS

I am grateful to V.N. Voronin and A.S. Dudin for their help in sampling the fish and for technical support of the work. The material was collected with the financial support from the Program of the Department of Biological Sciences of the Russian Academy of Sciences “Biological Resources of Russia: Dynamics in the Context of Global Climate and Anthropogenic Impacts.”

COMPLIANCE WITH ETHICAL STANDARDS

Сonflict of interests. The authors declare that they have no conflict of interest.

Statement on the welfare of animals. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.