The effectiveness of the induced anti-predator behaviour of zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> in the presence of molluscivorous roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis>

We checked whether the induced anti-predator defences of zebra mussels are able to affect the predation success of roach, being one of the most efficient zebra mussel predators in Europe. Previously, several anti-predator defences of mussels have been observed in the presence of roach, including stronger attachment, aggregation forming and inhibition of upward movement. However, the actual efficiency of these responses to reduce the mussel vulnerability to predation was unknown. To check the effectiveness of attachment strength, we exposed mussels for 6 (strong attachment), 1 (weak attachment) or 0 (unattached) days in ceramic trays and then presented the trays to fish in an experimental tank. To test the effectiveness of aggregation, we glued mussels to the trays in groups of three (touching one another) or singly using denture glue and exposed them to fish. To check the effect of the vertical position, we glued mussels with denture glue to the bottom and 10, 20 and 30 cm above the bottom of the tank with fish. After 1-h exposure, we determined the percentages of consumed mussels. Roach predation rate was lowest on strongly attached mussels, intermediate on weakly attached mussels and highest on unattached mussels. Aggregated mussels were less frequently consumed than singletons. Conversely, the vertical position of mussels did not affect the roach predation success. Our study demonstrates that the behavioural defences exhibited by zebra mussels can increase their survival in the presence of predators and thus emphasizes the importance of the anti-predator behaviour of this species.     

Natural hybridization of two mussel species <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas, 1771) and <Emphasis Type="Italic">Dreissena bugensis</Emphasis> (Andrusov, 1897)

Dreissenids display a high diversity of shell morphology, and it is frequently difficult to ascribe some individuals from mixed populations to one of the two species, Dreissena polymorpha (Pallas, 1771) or D. bugensis (Andrusov, 1897). Presumably, such individuals may be interspecific hybrids. We have analyzed species-specific allozyme loci of the typical representatives of these two mussel species and putative interspecific hybrids. A natural interspecific hybrid between D. polymorpha and D. bugensis was discovered for the first time by genetic methods. It has been demonstrated that D. bugensis was a maternal parent.     

Growth rate during early life affects sexual differentiation in roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>)

Many environmental factors have been shown to influence sex differentiation in fish, resulting in sex-biased populations, but the effects of growth rate have received limited attention. We conducted a controlled laboratory experiment in which growth rate and population density were manipulated in roach (Rutilus rutilus) during early development, and the subsequent effects on sex ratio determined. Significant differences in growth rate between fish populations were induced through provision of three different ration levels. In the slowest growing population there were fewer females compared within the fastest growing population (19% compared to 36% females), suggesting that in roach it may be more advantageous to become a small male than a small female when growth potential is limited. This may result from the fact that fecundity is limited by body size in female roach and that male roach are able to reproduce at a significantly smaller body size than females. In contrast, where roach were kept at different stocking densities, and there were no differences in growth rate, the subsequent proportion of females did not vary. Our data highlight the importance of controlling for growth rate in research on sexual differentiation in this species, notably when assessing for the effects of endocrine disrupting chemicals and other environmental factors, and have implications for fisheries management and aquaculture. The underlying mechanism for the influence of growth rate on sex differentiation has yet to be determined but is likely to have a strong endocrinological basis.     

Behavioral and morphological asymmetries in roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (Cyprinidae: Cypriniformes) underyearlings

The underyearlings of roach, Rutilus rutilus, displayed a bilateral asymmetry of C-bend—the initial stage of escape behavior. Most individuals exhibited a significant bias to turn leftward or rightward after being stimulated by electrical current. This individual asymmetry was consistent when the same fish were retested ten days later. A significant correlation was revealed between the behavioral asymmetry and the bilateral asymmetry of surface area of frontal (positive correlation) and parietal (negative correlation) cranial bones. No significant correlation was found with the bilateral asymmetry of other morphological characteristics: numbers of pores of the seismosensory canals (praeopercular-mandibular, supraorbital, and supratemporal) in flat cranial bones (dental, praeopercular, frontal, and parietal numbers of lateral line pores, and numbers of rays in pectoral and ventral fins.     

The limits of <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas) range in the Kama River basin

The distribution of Dreissena polymorpha in the northeastern part of the Kama River basin is limited to the area with the following geographic coordinates: 59°37′–54°00′ N and 57°10′–49°03′ E. The range of the zebra mussel is continuous along the Kama, Belaya, and Ufa rivers. Isolated populations of this mollusk exist in the Belaya and Vyatka river floodplains. The distribution of dreissena in the running waters of the Kama River basin is limited by the potamal conditions.     

Comparison of nutrition range in <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> and <Emphasis Type="Italic">Dreissena bugensis</Emphasis> mussels by biochemical markers

Based on biochemical markers, we studied the nutrition ranges of populations of Dreissena polymorpha and Dreissena bugensis mussels that inhabit the Volga reach of the Rybinsk reservoir and differ in the long-term population dynamics. Features of the nutrition ranges of mussels are regarded as the probable cause of changes in the number of mollusca.     

High prevalence of zoonotic trematodes in roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>) in the Gulf of Finland

The intention to increase roach (Rutilus rutilus) consumption is in focus for ecological and economic reasons in Finland. However, its safety as food has not been considered comprehensively. We collected and artificially digested 85 roach halves originating from the south-eastern coast of Finland, and found trematode metacercariae in 98.8% of the samples. Based on polymerase chain reaction (PCR) and sequencing of amplicons generated from the ITS2 gene region, zoonotic parasites of the family Opistorchiidae were identified as Pseudamphistomum truncatum and Metorchis bilis, and also non-zoonotic Holostephanus dubinini (family Cyathocotylidae) and Posthodiplostomum spp. (family Diplostomidae) were identified. The species identity of other trematodes found is currently being investigated. Mixed infections of several trematode species were common. The prevalence of morphologically identified zoonotic P. truncatum was 46%, and zoonotic M. bilis was found in one sequence sample. The high prevalence of zoonotic trematode metacercariae in roach from the Gulf of Finland is alarming. Only thoroughly cooked roach products can be recommended for human or animal consumption from the area.     

Variability in development of bilateral parts of the brain during ontogenesis of roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>)

A study exploiting the gravimetric method did not reveal identical development of paired parts of the roach (Rutilus rutilus) brain. In the studied sample, the proportion of fish with left or right asymmetry of this organ was 1: 1. The specificity of fluctuating asymmetry in studied plastic parameter depending on the fish age and growth was analyzed. In the ontogenetic sequence, from yearlings to nine-year-old fishes, the higher level of developmental instability was revealed in elder fish, six and more years old. Noted anatomical-morphological feature is likely determined by not only imperfect morphogenesis during early development: potential decrease in the threshold of noise immunity against unfavorable external and internal factors during later stages of fish development may contribute to the feature noted above. The analysis of sex-related traits revealed that in males fluctuating asymmetry of the brain bilateral parts is more pronounced.     

The zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>) impacts European bitterling (<Emphasis Type="Italic">Rhodeus amarus</Emphasis>) load in a host freshwater mussel (<Emphasis Type="Italic">Unio pictorum</Emphasis>)

The European bitterling, Rhodeus amarus, is a non-indigenous fish species in British fresh waters. It lays its eggs in unionid mussels which themselves are vulnerable to fouling by the non-indigenous zebra mussel, Dreissena polymorpha. Observations from an unmanipulated natural system showed that only 27% of zebra mussel-fouled Unio pictorum hosted bitterling, while 47% of unfouled U. pictorum hosted bitterling. We conducted a field experiment in the River Great Ouse catchment, Cambridgeshire, England in May–June 2007 and 2008 to quantify the impact of zebra mussels on bitterling load in host mussels. Zebra mussel-fouled unionids were significantly less likely to host bitterling than unfouled unionids. The number of unionids hosting bitterling did not differ significantly whether the zebra mussels fouling the unionid were alive or dead. Bitterling appeared to discriminate against zebra mussel-fouled unionids less as the 2007 breeding season advanced, potentially because preferred unfouled unionids had a higher bitterling load, and were therefore relatively lower quality hosts than at the start of the breeding season.     

The effect of raising conditions on behavior of juvenile roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) (Cyprinidae)

The behavior of juvenile 4.5-month-old roach Rutilus rutilus (L.) raised (starting on the 12th day after hatching) at different levels of habitat informational diversity (feeding with live and immobilized zooplankton and benthos, the presence of a predator, and a constant water flow in the nursery aquarium) was studied. The fish’s exploratory behavior and locomotor activity were tested in a circular chamber; swimming activity was tested in a hydrodynamic conduit. It was experimentally shown that juvenile roach raised in the presence of a predator differed significantly (p < 0.05) in regards to behavioral characteristics from the fries raised in a water current and in conditions of a high level of environmental deprivation.     

Specific features of thermoregulation behavior in early juveniles of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> under thermogradient conditions

Specific features of thermoregulation behavior were studied, and values of the selected and final selected temperature (25.1°C) for early juveniles of roach Rutilus rutilus aged 11–28 days after hatching were first studied in long-term experiments (16 days). Two periods of the process of thermoselection—transient (selected temperature, up to 7–9 days after the beginning of the experiment) and final (final selected temperature, 8–10 days after the beginning of the experiment)—have been identified. The selection by larval roach of final selected temperature values occurs with use of the adaptation response of “excessive responding.” It was shown that correct determination of final selected temperature values for early juveniles of fish is possible only in long-term experiments (more than 7 days). The obtained results can be used during the analysis of behavior and distribution of larval roach under natural and experimental conditions.     

Zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>) affects the feeding ecology of early stage striped bass (<Emphasis Type="Italic">Morone saxatilis</Emphasis>) in the Hudson River estuary

Variability in the feeding ecology of young fishes over short and long time scales in estuaries is likely to affect population dynamics. We studied 14 years of early stage Striped Bass feeding ecology in the Hudson River Estuary over a 25-year time span, including years in which invasive zebra mussels markedly altered energy flow within the estuary. We predicted that feeding success would be low and that diet composition would be altered during years of high zebra mussel impact, particularly in upriver locations where mussels occur. Feeding success in the short term was indicated by volume of gut contents and in the long term by dry mass at length, i.e. condition; these measures were positively intercorrelated and varied significantly year to year. We tested for associations between condition and multiple biotic and abiotic environmental variables. There was a strong negative effect of zebra mussel grazing rate on condition in upriver locations and a weak positive effect in downriver locations. In upriver locations, condition was 33% higher when local salinity was high and zebra mussel grazing rates were low, whereas in downriver locations, condition was 35% higher when zebra mussel grazing rates and copepod abundance were high and local dissolved oxygen was low. Copepods, amphipods, mysids, and Leptodora constituted the highest prey-specific index of relative importance throughout the estuary. There was no evident effect of the zebra mussel invasion on diet composition. This long-term study corroborates the inferences of earlier studies that zebra mussels reduced early-stage striped bass growth rate.     

Genetic diversity of the cytochrome b gene fragment haplotypes in red-backed vole <Emphasis Type="Italic">Myodes</Emphasis> (<Emphasis Type="Italic">Clethrionomys</Emphasis>) <Emphasis Type="Italic">rutilus</Emphasis> Pallas, 1779

For the first time, genetic analysis of the cytochrome b gene fragment haplotypes encoding the identical and the most common cytochrome b polypeptide (F1) in M. rutilus from eastern and Beringian maternal lineages was carried out. The F1 frequencies for the vole populations from Northern Priokhotye and the Kolyma basin were calculated. Considerable polymorphism of the cytochrome b F1 haplotypes within two major phylogroups of red-backed vole was supported by high molecular diversity indices for these clades. The proportion of genetic variation between the maternal lineages of F1 red-backed vole individuals (60.71%) was considerably higher than inter(24.44%) and intrapopulation (14.85%) components. The data obtained make it possible to advance a hypothesis on the convergence of the cytochrome b polypeptide structure upon sequence divergence of the corresponding gene.     

Effect of thyroid hormones on the development of pharyngeal dentition in roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (Cyprinidae,Cypriniformes)

Development of teeth on the pharyngeal bones of roach Rutilus rutilus and the effect of thyroid hormones on this development are investigated. The addition of exogenous triiodothyronine leads to accelerated development of the teeth, but the deficit of triiodothyronine (provoked by the addition of thiourea in the media) stimulates the retardation of this development. Change of developmental rate of the organism leads to change in the definitive state of the pharyngeal teeth formula. Owing to accelerated development, the number of teeth significantly decreases, and the formulas 5–5, 5–4, and 4–4 appear instead of the typical formula 6–5 in the control group and in the fish from natural populations. Retarded development of the organism leads to increased frequency of occurrence of the formula 6–6. The directed asymmetry in the numbers of pharyngeal teeth with the formula (6–5), most likely, is connected with different types of teeth development on the left and right pharyngeal bones.     

The role of thyroid hormones in the formation of behavioral responses in juvenile roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) (Cyprinidae)

The effect of thyroid hormones (THs) on the formation of behavioral responses in juvenile roach was studied. Eggs taken from one pair of spawners were split into three groups and kept in different environments: a clean water control, with the addition of a hormone, and with the addition of a substance blocking thyroid-gland synthetic activity. It was revealed that control fish and those with an enhanced hormonal status manifest more mature behavior than the fish with a lowered hormonal status.     

Morphological variation in <Emphasis Type="Italic">Laboulbenia polymorpha</Emphasis> (Laboulbeniales)

Specimens of the type collection of Laboulbenia polymorpha Sugiyama (1978) were reexamined. The holotype, M. Ishikawa 673, is composed of three slides and includes three morphologically different forms of thalli, of which two forms were illustrated (Sugiyama 1978, fig. 1-D, 1-E). On the other hand, one of the paratypes, M. Ishikawa 674, has now been lost but photographs were made earlier from this slide, in which one mature individual illustrated as fig. 1-C (Sugiyama 1978) is included. This individual was not correctly shown in Sugiyamas illustration, but actually has a strong resemblance to a form in slide 673-b that was not illustrated by Sugiyama (1978). Thus, three different forms have been recognized as variations of L. polymorpha. In the present article, each variation was termed C-form, D-form, and E-form because Sugiyama (1978) used the same notation in his figures. A mature specimen of C-form in slide 673-b has been selected as a lectotype. Slide 673-d includes only young thalli, one of which was illustrated as fig. 1-G (Sugiyama 1978). This young thallus undoubtedly belongs to another species; mature thalli of the same species were also found in slide 673-b. Another paratype, K. Sugiyama 2101, includes C- and D-forms of L. polymorpha. Infection sites of the C- and D-forms have been determined: the C-form grows mainly on the lateral margins of the elytra of the host, and the D-form occurs mainly on the basal part of the elytra and the mesothorax.     

Cryopreservation of <Emphasis Type="Italic">Marchantia polymorpha</Emphasis> spermatozoa

The liverwort Marchantia polymorpha has become one of the model organisms, since it has less genetic redundancy, sexual and asexual modes of reproduction and a range of genomic and molecular genetic resources. Cryopreservation of fertile spermatozoa eliminates time, space and labor for growing and maintaining male plants in reproductive phase, and also provides an optional way to backup lines. Here we report a protocol to cryopreserve spermatozoa of M. polymorpha in liquid nitrogen. A cryoprotective solution containing sucrose, glycerol and egg yolk and controlled cooling and warming processes led to successful recovery of motile M. polymorpha spermatozoa after the cryogenic process. The survival rate and average motility of spermatozoa after cryopreservation were maintained at 71 and 54% of those before cryopreservation, respectively. Cryopreserved spermatozoa were capable of fertilization to form normal spores. The technique presented here confers more versatility to experiments using M. polymorpha and could be applied to preservation of plant spermatozoa in general.     

Threshold environmental concentrations of cations defining the range of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> L. in freshwater reservoirs

Threshold levels of sodium, potassium, calcium, and magnesium that define the distribution range of roach in fresh water are 0.015–0.019, 0.012–0.015, 0.006–0.009, and 0.002–0.003 mmol/L, respectively. A reduction in water mineralization is accompanied by a significant decrease in the concentration gradient of cations between the organism of a fish and the environment and by the increased stress on the systems responsible for salty exchange. Many reservoirs are characterized by lower concentrations of potassium in the water than is needed for the success of the roach population. The survival of roach in these waterbodies depends on the amount of potassium consumed by fish with their food. A comparative analysis is performed to assess the threshold levels of cations for roach, two bivalve mollusk species, crayfish, and the filamentous algae Spirogyra.     

Reproductive parameters of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) from the Rybinsk Reservoir reaches differing in anthropogenic loads

The results of a study on the parameters of reproductive capacity in roach from the Sheksna and the Volga reaches of the Rybinsk Reservoir are presented. The Volga reach is relatively clean, while the Sheksna reach is subject to the strongest anthropogenic load. In 2011, the average values of the absolute and relative fecundity, as well as the egg size, in roach Rutilus rutilus (L.) from the Volga reach were higher than those in roach from the Sheksna reach, but differences are mainly statistically insignificant. The data of the study indicate the adaptation of the investigated roach to the negative influence of the Sheksna reach contamination and, in particular, its preservation of a sufficient level of reproductive capacity.