Kateřina Rylková

Massive mortality of Prussian carp Carassius gibelio in the upper Elbe basin associated with herpesviral hematopoietic necrosis (CyHV-2)

From 22 May to 10 June 2011 massive mortality of Prussian carp Carassius gibelio was observed in alluvial Lake Řehacˇka close to the Elbe River in the Czech Republic. More than 1400 kg of dead fish were collected and no other fish species were affected. Further molecular and cytogenetic investigation of fish (n = 232) revealed that the Rˇehacˇka population of Prussian carp consisted exclusively of gynogenetic triploid females. The causative agent was identified by means of molecular and electron microscopy as a herpesviral hematopoietic necrosis virus (Cyprinid herpesvirus 2, CyHV-2). This is the first report of CyHV-2 from the Czech Republic and the second finding worldwide of CyHV-2 causing mass mortality of C. gibelio. Some other localities in the upper Elbe River basin where C. gibelio was affected are also noted. We assume that the massive wave of deaths of all female gynogenetic Prussian carp can be attributed to limited genetic variation and the favourable conditions for development of viral disease.

Aquarium hitchhikers: attached commensals imported with freshwater shrimps via the pet trade.

The keeping of home aquaria is one of the most popular hobbies globally. In contrast to the ornamental fish trade, decapod crustaceans such as shrimps, crayfish and crabs are relatively new to the pet trade. Nevertheless, the popularity of ornamental shrimp in freshwater aquaria has rapidly increased in recent years. Indonesia is one of the leading producers and exporters of ornamental aquatic animals globally and the Czech Republic is a gateway for these animals into the European Union territory. The pathway for introductions of organisms unintentionally moved in association with ornamental shrimps via the international trade has to date not been evaluated. We examined a small number of shrimps imported from Indonesia into the Czech Republic in May 2015 and found large numbers of the protozoan Vorticella sp., one species of scutariellid temnocephalidan (Caridinicola sp.), and one species of bdelloid rotifer, associated with two species of atyid shrimps, indicating an invasion risk from fauna carried unintentionally by this vector. Although our observations were limited in scale, we estimate the total number of commensal fauna imported into the Czech Republic with ornamental shrimps via the pet trade to be in the order of hundreds of thousands per month. As attached organisms can directly or indirectly cause diseases in certain species of decapod crustaceans, we recommend five steps to reduce risks of introduction of “hitchhikers” to aquaria and wildlife.

Chromosome studies of European cyprinid fishes: cross-species painting reveals natural allotetraploid origin of a Carassius female with 206 chromosomes.

A single female with 206 chromosomes and another 26 females with 156 chromosomes identified as Prussian carp, Carassius gibelio, and 5 individuals with 100 chromosomes identified as crucian carp, C. carassius, were sampled during field survey in one locality in the upper Elbe River. To identify the origin of females with high chromosome numbers, comparative karyotype analysis, GISH, with whole C. carassius DNA as probe and phylogenetic positions of sampled individuals revealed by cytochrome b mitochondrial marker were performed. GISH showed consistently bright labeling of 50 chromosomal elements out of 206, corresponding to the haploid chromosome number of C. carassius. The position of these females with high chromosome numbers in a reconstructed phylogenetic tree was within the clade of C. gibelio, documenting its affiliation to C. gibelio mitochondrial, i.e. maternal lineage. Our findings indicated that the mother of the female with high chromosome numbers was a gynogenetically reproducing 156-chromosome C. gibelio female and the father a bisexually reproducing C. carassius male. We, therefore, hypothesized that the C. gibelio × C. carassius allopolyploid female with 206 chromosomes arose by a mechanism of sperm genome addition to an unreduced egg of the mother.

Population-specific responses to an invasive species

Predicting the impacts of non-native species remains a challenge. As populations of a species are genetically and phenotypically variable, the impact of non-native species on local taxa could crucially depend on population-specific traits and adaptations of both native and non-native species. Bitterling fishes are brood parasites of unionid mussels and unionid mussels produce larvae that parasitize fishes. We used common garden experiments to measure three key elements in the bitterling–mussel association among two populations of an invasive mussel (Anodonta woodiana) and four populations of European bitterling (Rhodeus amarus). The impact of the invasive mussel varied between geographically distinct R. amarus lineages and between local populations within lineages. The capacity of parasitic larvae of the invasive mussel to exploit R. amarus was higher in a Danubian than in a Baltic R. amarus lineage and in allopatric than in sympatric R. amarus populations. Maladaptive oviposition by R. amarus into A. woodiana varied among populations, with significant population-specific consequences for R. amarus recruitment. We suggest that variation in coevolutionary states may predispose different populations to divergent responses. Given that coevolutionary relationships are ubiquitous, population-specific attributes of invasive and native populations may play a critical role in the outcome of invasion. We argue for a shift from a species-centred to population-centred perspective of the impacts of invasions.

The first determination of Trichuris sp. from roe deer by amplification and sequenation of the ITS1-5.8S-ITS2 segment of ribosomal DNA

Trichuris nematodes were isolated from roe deer (Capreolus capreolus). At first, nematodes were determined using morphological and biometrical methods. Subsequently genomic DNA was isolated and the ITS1-5.8S-ITS2 segment from ribosomal DNA (RNA) was amplified and sequenced using PCR techniques. With u sing morphological and biometrical methods, female nematodes were identified as Trichuris globulosa, and the only male was identified as Trichuris ovis. The females were classified into four morphotypes. However, analysis of the internal transcribed spacers (ITS1-5.8S-ITS2) of specimens did not confirm this classification. Moreover, the female individuals morphologically determined as T. globulosa were molecularly identified as Trichuris discolor. In the case of the only male molecular analysis match the result of the molecular identification. Furthermore, a comparative phylogenetic study was carried out with the ITS1 and ITS2 sequences of the Trichuris species from various hosts. A comparison of biometric information from T. discolor individuals from this study was also conducted.

Occurrence of bifidobacteria and lactobacilli in digestive tract of some freshwater fishes

Distal parts of the fish intestine were analyzed for presence of bifidobacteria and lactobacilli using selective agars. Seventy seven samples from Cyprinus carpio, Oncorhynchus mykiss, Carassius auratus, Tinca tinca, Perca fluviatilis, Rutilus rutilus, Scardinius erythrophthalmus, Oreochromis niloticus, and Squalius cephalus were collected randomly throughout years 2008 and 2009. Bifidobacteria were detected in 5 samples from 4 fish species at counts 2.18–4.29 log CFU/g, lactobacilli were present in 6 fish species at counts 1.21–3.65 log CFU/g. Seven bifidobacterial isolates were identified to the species level using biochemical tests and by sequencing of 16S rRNA gene. Three strains belonged to species B. longum, two isolates were identified as B. dentium, one strain as B. asteroides and one isolate was not determined to the species level by employed methods. As identified bifidobacterial species are considered to be of human, animal or honeybee origin, they probably derived as contamination from sewage or other sources. After further more detail testing, the possible use of isolated bifidobacteria as probiotics is promising since they were able to pass through the digestive tract successfully.

New mtDNA data reveal a wide distribution of the Japanese ginbuna Carassius langsdorfii in Europe.

In this study, records on the occurrence of the Japanese ginbuna Carassius langsdorfii from northern Germany, north-western Italy and southern Bosnia and Herzegovina are presented. The new findings, in addition to former studies reported in the Czech Republic and Greece, show that C. langsdorfii is much more widespread in Europe than was previously believed.

Morphologically indistinguishable hybrid Carassius female with 156 chromosomes: A threat for the threatened crucian carp, C. carassius, L

The crucian carp Carassius carassius (Linnaeus, 1758), is native to many European freshwaters. Despite its wide distribution, the crucian carp is declining in both the number and sizes of populations across much of its range. Here we studied 30 individuals of a putative pure population from Helsinki, Finland. Despite clear external morphological features of C. carassius, an individual was of a higher ploidy level than the others. We therefore applied a set of molecular genetic (S7 nuclear and cytochrome b mitochondrial genes) and cytogenetic tools (sequential fluorescent 4’, 6-diamidino-2-phenylindole [DAPI], Chromomycin A3 [CMA3], C-banding and in situ hybridization [FISH] with both 5S and 28S ribosomal DNA probes) to determine its origin. While all examined characteristics of a diploid representative male (CCAHe2Fi) clearly corresponded to those of C. carassius, a triploid individual (CCAHe1Fi) was more complex. Phylogenetic analysis revealed that the nuclear genome of CCAHe1Fi contained three haploid sets: two C. gibelio and one C. carassius. However the mitochondrial DNA was that of C. gibelio, demonstrating its hybrid origin. The FISH revealed three strong (more intensive) 5S rDNA loci, confirming the triploid status, and an additional 24 weak (less intensive) signals were observed in the chromosome complement of CCAHe1Fi. On the other hand, only two strong and 16 weak 5S rDNA signals were visible on the chromosomes of the CCAHe2Fi male. 28S rDNA FISH revealed four strong signals in both CCAHe1Fi and CCAHe2Fi individuals. CMA3 staining revealed four to six CMA3-positive bands of CCAHe1Fi, while that of diploids contained only two to four. The fact that a polyploid hybrid Carassius female with a strong invasive potential may share morphological characters typical for endangered C. carassius highlights a need to combine genetic investigations of Carassius cryptic diversity with conservation measures of C. carassius in Europe.

Radio-telemetry shows differences in the behaviour of wild and hatchery-reared European grayling Thymallus thymallus in response to environmental variables.

Juvenile wild and hatchery-reared European grayling Thymallus thymallus were tagged with radio-transmitters and tracked in the Blanice River, River Elbe catchment, Czech Republic, to study their behavioural response to stocking and environmental variation. Both wild and hatchery-reared T. thymallus increased their diel movements and home range with increasing light intensity, flow, temperature and turbidity, but the characteristics of their responses differed. Environmental variables influenced the movement of wild T. thymallus up to a specific threshold, whereas no such threshold was observed in hatchery-reared T. thymallus. Hatchery-reared fish displayed greater total migration distance over the study period (total migration) than did wild fish, which was caused mainly by their dispersal in the downstream direction.

Prussian carp Carassius gibelio: a silent invader arriving to the Iberian Peninsula

In the last decades, the invasive Prussian carp, Carassius gibelio, has been detected in most of the European countries. The Prussian carp has been undetected in many European countries since it is morphologically indistinct from the long-established goldfish Carassius auratus. In this study, genetic markers were used to identify the Prussian carp in several locations of the Iberian Peninsula (Portugal and Spain). The presence of polyploid C. gibelio is confirmed for the first time in Iberian Peninsula, in four large river systems (Guadalquivir, Guadiana, Tagus and Douro). The introduction of C. gibelio to these Iberian drainages is discussed in light of the potential vector to the Iberian Peninsula.