Ján Koščo

Non-native fish species in Slovak waters: origins and present status

Freshwater fishes recorded in the territory of Slovakia include 95 fish species. As many as one third of these are allochthonous fish species belonging to 14 families, among which several have not occurred in Slovakia recently. Historically, there were three main periods of introduction: the first is the beginning of the 20th century, the second includes two decades between 1955 and 1975 and the third period is from the year 1990 up to the present time. The origins of the exotic species seen in Slovakia are the four continents — Africa (3), North America (7), Central America (3), and Asia (13) and ten of them are from different regions in Europe. The purpose of intentional introductions of non-native species was to occupy vacant ecological niches in the ecosystems reshaped by human activities, fish stocking, angling or fish farming. Some of these species spread from their original ranges or they penetrated spontaneously from the adjacent countries via the river network system. At the present time, 76 fish species in total form populations in Slovakia. There are 54 autochthonous and 22 allochthonous species, 14 of them are exotic fishes. The invasive characters in 13 fish species were considered, the recent native/total fish ratio is 0.71.

New records of endoparasitic helminths in alien invasive fishes from the Carpathian region.

Six non-native invasive fish species from the Slovak part of the Tisa River basin, namely Carassius gibelio, Pseudorasbora parva, Ameiurus melas, A. nebulosus, Lepomis gibbosus, Perccottus glenii, and three gobiid species from the Danube River, namely Neogobius melanostomus, N. fluviatilis and N. kessleri, were investigated for endohelminth parasites. The expanding Asian cestode Nippotaenia mogurndae (syn. Amurotaenia perccotti) (Nippotaeniidea) has been introduced to Europe with its invasive host P. glenii. Pumpkinseed, Lepomis gibbosus, is a new definitive host of Proteocephalus percae and it is reported as the second intermediate host of the bothriocephalidean cestode Triaenophorus nodulosus in Slovakia.

New data on an exotic Nippotaenia mogurndae (Cestoda), newly introduced to Europe

SummaryData on prevalence and current distribution of the cestode Nippotaenia mogurndae Yamaguti and Miyata, 1940 (Nippotaeniidea) in Slovakia, are provided. A total of 163 fish from 8 localities of different types in the Tisa River basin were infected with N. mogurndae. The mean intensity of infection was 1.8 with a maximum of 5 tapeworms. The expansion of the distribution of the cestode corresponds well with the spreading of its host, the invasive fish Amur sleeper Perccottus glenii Dybowski, 1877. The Spearmann correlation coefficient was used to test the relationship between the intensity of infection and standard length of the fish (r = 0.36; n = 163; P < 0.05), condition coefficient of the fish (r = 0.22; n = 115; P < 0.05) and season (r = −0.37; n = 355; P < 0.05). A significant correlation was confirmed for each pair of variables. There is a statistically significant difference between the prevalence of the cestode in two functional size groups (t = 3.28; n = 163; P < 0.05). The prevalence of the cestode increased with the standard length of fish. The potential risk of further expansion of N. mogurndae to other countries is discussed.

Longitudinal structure of fish assemblages in a minimally disrupted stream

The longitudinal distribution patterns of fish species are affected by both natural and anthropogenic variables. The role of these factors on the formation of species assemblages is well documented in North America and Western Europe, but detailed information is lacking from Central and Eastern Europe, and the Carpathian region especially. Therefore, we examined the structure of fish assemblages in response to six key environmental parameters in a natural stream system (Udava stream basin, Slovakia). We used the indirect ordination method of gradient analysis (Detrended Correspondence Analysis, DCA) to analyse the species groups and their connections to the sampled sites and to recognize the strongest gradient of assemblage composition. Subsequently, we used the direct ordination method (Canonical Correspondence Analysis, CCA) to identify the strongest gradients in relation to selected variables. Two major gradients were identified that follow the upstream-downstream pattern of fish communities and three variables (distance from source, depth and site slope) are correlated with the first CCA axis (P < 0.05) and two variables (depth and vegetation cover) are correlated with the second CCA axis (P < 0.05). We assume that these factors influence the temperature and the amount of dissolved oxygen that can cause oxygen and temperature stress to intolerant species (e.g., salmonids). Based on these results, we assume that the economically important species, brown trout and grayling, are not native to the stream basin and this status is only the consequence of natural factors. Furthermore, the results suggest that the Udava stream offers favourable conditions for fish species distribution — a view supported by the high variability of particular variables within the proposed model.

Growth differences in different biotypes of the hybrid complex of Cobitis elongatoides × Cobitis tanaitica (Actinopterygii: Cypriniformes: Cobitidae) in the Okna River (Danube River basin), Slovakia

Background. Many of Cobitis subpopulations exist as diploid–polyploid hybrid complexes where polyploid gynogenetic females act as “sperm parasites” of diploid individuals. In addition to sexual strategy, the life history of such individuals is also affected by their growth performance. In order to elucidate unknown aspects of the Cobitis hybrid complexes we decided to identify differences in the annual size increments between individuals representing different ploidy and sex, and to compare the condition factor expressed by length–weight (L–W) relation within the same ploidy and sex groups. Material and methods. In total, 158 specimens representing Cobitis elongatoides (Băcescu et Mayer, 1969) × Cobitis tanaitica (Băcescu et Mayer, 1969) hybrid complex were caught in August and September 2014, of which 132 were analysed. The fish were caught in the Okna River (Danube River basin), Slovakia. Sex was determined based on externally visible morphological features or based on microscopic observation of the gonads. Ploidy level was determined by means of flow cytometry on fin clips taken from each specimen. Age was estimated based on the total number of annuli visible on vertebrae. All statistical models were performed in the R statistical environment. Results. Sex ratio varied within age classes, with 3+ fish primarily composed of females and, 4+ fish mostly triploid. Maximum back-calculated lengths for diploid females were obtained up to 3+, and for the 4+ age group for triploid. L–W relations for adult males and females also differed significantly, but did not vary between diploid and triploid females. There were differences in at specific body lengths for Cobitis with different ploidy level. Diploid males were characterised by short annual age and length increments during the first two years of life. Annual increments in diploid females were highest overall though their frequency decreased after the reaching the fourth year of life (3+). On the contrary, annual increments in triploid females were the lowest within all groups until their fourth year, thought their frequency in the oldest age group (4+). Conclusion. In our study, we first confirmed that yearly increments and maximal age of Cobitis individuals are affected by different ploidy. Contrary, the L–W relations of gutted diploid and triploid females did not differ and they were affected only by sex. We suggest that the intensity of growth is more affected by ploidy, while the L–W of Cobitis is determined by intensity of feeding and stage of gonad development at the local conditions during season. Therefore, in the future studies of Cobitis growth and condition parameters the ploidy level of individuals should also be considered.

First report of Gussevia asota (Monogenea: Dactylogyridae), destructive parasite of A stronotus ocellatus (Perciformes: Cichlidae) in Europe

Abstract During epizootological monitoring of local pet-shops and aquarium fish breeders, 45 juvenile fish of Astronotus ocellatus Agassiz, 1831 were examined in March 2013 and October 2014. Fish were imported from a Singapore farm. We found massive infection by Gussevia asota Kritsky, Thatcher & Boeger, 1989 with 100% prevalence and high mean intensities 246 and 265 parasites. Fish displayed visible asphyxia, neurological symptoms, uncoordinated locomotion and sudden death. High 98% mortality of imported juveniles suggests reduced capacity to tolerate hypoxia among oscar juveniles. This is the first report of infection by G. asota in A. ocellatus juveniles in commercial shop from Slovak Republic, in Europe.

Juvenile red swamp crayfish growth affected by isolation from their mother

Abstract The red swamp crayfish (Procambarus clarkii Girard, 1852) which is indigenous to North America, is the most commercially exploited species in astaciculture. Farming profitability depends mainly on crayfish growth rates. Thus research focused on factors affecting growth of crayfish is of high priority in this sector of aquaculture. Growth rate retardation related to social deprivation in crayfish has never been evaluated in crustaceans. The present experiment was carried out in order to compare growth rates of the Stage 3 juvenile red swamp crayfish from two offspring origins: maternal incubation and early separation from the mother. Juveniles were kept in three types of groups composed each by six individual: maternal incubated, early separated, and mix of both of them. Offspring origin significantly affected juvenile crayfish growth rates when maternally incubated individuals grew faster than crayfish from the other two group types. Moreover, the same significant differences were shown in number of moults. The results of the present study provide new insight into crayfish behaviour related to prior social experience of juveniles, but future studies are needed to verify our assumption.

Frequency of new marble-colored morph in wild population of Austropotamobius torrentium (Decapoda: Astacidae)

In contrast with the usual coloration of stone crayfish (Austropotamobius torrentium), we newly discovered a rare marble morph in a brook in the Czech Republic (Central Europe). During mark-recapture sessions, we captured by hand 1,103 individuals over the 3 years 2008–2010 from which only 5 were marble-colored. This color morph’s frequency of occurrence was thus less than 1% within the estimated subadult and adult stone crayfish population. Although many biological papers and determination keys regarding crayfish are based upon analysis of exoskeletal coloration, recent studies have asserted that this characteristic provides unreliable guidance when determining species inasmuch as it easily results in errors because many crayfish species exhibit an extensive variety of color morphs.

The first record of Piscicola fasciata (Hirudinea, Piscicolidae) in Slovakia

Material examined: E Slovakia, Latorica River at Kamenná Moľva, 2 km east from the village of Brehov (48◦29′15′′ N, 21◦51′ E), altitude 95 m a.s.l., 34 ind. 13–40 mm long, attached on the head, mainly the beard and gill covers of Silurus glanis L., 1758 (105 cm in length), 4.VII.2003, leg. Koščo. Remarks: Piscicola fasciata is a specific parasite of S. glanis and differs from the other European fish leeches by very large anterior and posterior suckers, the posterior one exceeds the diameter of the body minimally two times. We suppose that the distribution of this leech in Slovakia follows mostly that of S. glanis. Distribution: The geographical distribution of this leech covers the ponto-Caspian basin (LUKIN, 1976). It has been found in all the countries bordering with Slovakia: the Czech Republic (LUCKÝ & DYK, 1964), Poland (PAWLOWSKI, 1968; BIELECKI, 1978), Ukraine (ERGENS et al., 1975; LUKIN, 1976), Hungary (SOÓS, 1964; NESEMANN, 1994) and Austria (NESEMANN, 1994). References