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The aim of the study was to verify whether the use of heparin as an anticoagulant can affect the results of genome size measurements using a flow cytometer. The values obtained by measuring blood samples with different concentrations of heparin were compared. The differences observed were highly significant, suggesting that the results of previous comparative studies, or those determining individual polyploidy, may need reinterpretation. We anticipate that our findings will increase the accuracy of flow cytometric analysis and will be useful for further surveys of genome size undertaken using blood samples.

Interspecific hybridization may trigger the transition from sexual reproduction to asexuality, but mechanistic reasons for such a change in a hybrid’s reproduction are poorly understood. Gametogenesis of many asexual hybrids involves a stage of premeiotic endoreplication (PMER), when gonial cells duplicate chromosomes and subsequent meiotic divisions involve bivalents between identical copies, leading to production of clonal gametes. Here, we investigated the triggers of PMER and whether its induction is linked to intrinsic stimuli within a hybrid’s gonial cells or whether it is regulated by the surrounding gonadal tissue. We investigated gametogenesis in the Cobitis taenia hybrid complex, which involves sexually reproducing species (Cobitis elongatoides and C. taenia) as well as their hybrids, where females reproduce clonally via PMER while males are sterile. We transplanted spermatogonial stem cells (SSCs) from C. elongatoides and triploid hybrid males into embryos of sexual species and of asexual hybrid females, respectively, and observed their development in an allospecific gonadal environment. Sexual SSCs underwent regular meiosis and produced normally reduced gametes when transplanted into clonal females. On the other hand, the hybrid’s SSCs lead to sterility when transplanted into sexual males but maintained their ability to undergo asexual development (PMER) and production of clonal eggs, when transplanted into sexual females. This suggests that asexual gametogenesis is under complex control when somatic gonadal tissue indirectly affects the execution of asexual development by determining the sexual differentiation of stem cells and once such cells develop to female phenotypes, hybrid germ cells trigger the PMER from their intrinsic signals.

Despite its inherent costs, sexual reproduction is ubiquitous in nature, and the mechanisms to protect it from a competitive displacement by asexuality remain unclear. Popular mutation‐based explanations, like the Muller's ratchet and the Kondrashov's hatchet, assume that purifying selection may not halt the accumulation of deleterious mutations in the nonrecombining genomes, ultimately leading to their degeneration. However, empirical evidence is scarce and it remains particularly unclear whether mutational degradation proceeds fast enough to ensure the decay of clonal organisms and to prevent them from outcompeting their sexual counterparts. To test this hypothesis, we jointly analysed the exome sequences and the fitness‐related phenotypic traits of the sexually reproducing fish species and their clonal hybrids, whose evolutionary ages ranged from F1 generations to 300 ky. As expected, mutations tended to accumulate in the clonal genomes in a time‐dependent manner. However, contrary to the predictions, we found no trend towards increased nonsynonymity of mutations acquired by clones, nor higher radicality of their amino acid substitutions. Moreover, there was no evidence for fitness degeneration in the old clones compared with that in the younger ones. In summary, although an efficacy of purifying selection may still be reduced in the asexual genomes, our data indicate that its efficiency is not drastically decreased. Even the oldest investigated clone was found to be too young to suffer fitness consequences from a mutation accumulation. This suggests that mechanisms other than mutation accumulation may be needed to explain the competitive advantage of sex in the short term.

Interspecific hybridization may trigger the transition from sexual reproduction to asexuality, but mechanistic reasons for such a change in a hybrid’s reproduction are poorly understood. Gametogenesis of many asexual hybrids involves a stage of premeiotic endoreduplication (PMER), when gonial cells duplicate chromosomes and subsequent meiotic divisions involve bivalents between identical copies, leading to production of clonal gametes. Here, we investigated the triggers of PMER and whether its induction is linked to intrinsic stimuli within a hybrid’s gonial cells or whether it is regulated by the surrounding gonadal tissue.We investigated gametogenesis in theCobitis taeniahybrid complex, which involves sexually reproducing species (Cobitis elongatoidesandC. taenia) as well as their hybrids, where females reproduce clonallyviaPMER while males are sterile. We transplanted spermatogonial stem cells (SSCs) fromC. elongatoidesand triploid hybrid males into embryos of sexual species and of asexual hybrid females, respectively, and observed their development in an allospecific gonadal environment. Sexual SSCs underwent regular meiosis and produced normally reduced gametes when transplanted into clonal females. On the other hand, the hybrid’s SSCs lead to sterility when transplanted into sexual males, but maintained their ability to undergo asexual development (PMER) and production of clonal eggs, when transplanted into sexual females.This suggests that asexual gametogenesis is under complex control when somatic gonadal tissue indirectly affects the execution of asexual development by determining the sexual differentiation of stem cells and once such cells develop to female phenotypes, hybrid germ cells trigger the PMER from their intrinsic signals.Significance StatementAlthough sexual reproduction is a dominant trait among all eukaryotes, many taxa have evolved the ability to reproduce asexually. While asexuality appears to be linked to interspecific hybridization, it remains unknown how the coexistence of diverged genomes may initiate such a swap in reproduction. In our study, we transplanted germ cells between asexual hybrids and their parents. On one hand, the ability of clonal gametogenesis occurred exclusively in hybrid germ cells, suggesting that asexual development is directly triggered by the hybrid genomic constitution of the cell. On the other hand, clonality was observed only in cells transplanted into females, suggesting that the execution of clonal development is influenced by signals from the gonadal environment and regulated by somatic factors.

Hybridization and polyploidization are important evolutionary processes whose impacts range from the alteration of gene expression and phenotypic variation to the triggering of asexual reproduction. We investigated fishes of the Cobitis taenia-elongatoides hybrid complex, which allowed us to disentangle the direct effects of both processes, due to the co-occurrence of parental species with their diploid and triploid hybrids. Employing morphological, ecological, and RNAseq approaches, we investigated the molecular determinants of hybrid and polyploid forms. In contrast with other studies, hybridization and polyploidy induced relatively very little transgressivity. Instead, Cobitis hybrids appeared intermediate with a clear effect of genomic dosing when triploids expressed higher similarity to the parent contributing two genome sets. This dosage effect was symmetric in the germline (oocyte gene expression), interestingly though, we observed an overall bias toward C. taenia in somatic tissues and traits. At the level of individual genes, expression-level dominance vastly prevailed over additivity or transgressivity. Also, trans-regulation of gene expression was less efficient in diploid hybrids than in triploids, where the expression modulation of homoeologs derived from the “haploid” parent was stronger than those derived from the “diploid” parent. Our findings suggest that the apparent intermediacy of hybrid phenotypes results from the combination of individual genes with dominant expression rather than from simple additivity. The efficiency of cross-talk between trans-regulatory elements further appears dosage dependent. Important effects of polyploidization may thus stem from changes in relative concentrations of trans-regulatory elements and their binding sites between hybridizing genomes. Links between gene regulation and asexuality are discussed.

Alizarin Red S marking and detection was tested on asp (Leuciscus aspius Linnaeus, 1758) in an experimental pool followed by a mark-recapture experiment in the field. Placing the asp in a 0.15 g L−1 solution for one hour produced marks that were detectable for at least one year. In order to detect the fluorescent marks, novel equipment was developed comprising a battery-powered laser source (

Loaches (genus Cobitis) in Slovakian tributaries (Danube River Basin) are represented by diploid-polyploid hybrid complexes of C. elongatoides and C. tanaitica. Uniquely, their coexistence is made possible by the presence of polyploid (mainly triploid) females that are sexually dependant on diploid male sperm (donors) for gynogenesis. Information on the spatial distribution of Cobitis with of differing ploidy remains relatively scarce. The main aim of this study, therefore, was to identify in ploidy in the species preferred microhabitat. Overall, 345 Cobitis were recorded in Rivers Okna and Ondava (Danube Basin) between 2011 and 2015, with 316 diploid and triploid individuals detected by flow cytometry examined were studied for the microhabitat preferences with the using the point sample method. The sex ratio differed significantly between localities, while diploid-polyploid ratio not. Moreover, each of ploidy-sex forms (i.e. diploid male, diploid female, triploid female) showed a preference for a specific substrate composition, velocity, depth and distance from the bank at both localities. Mixed effect linear models identified clear differences in fine substrate between seasons for individuals from the River Okna. Similarly, non-metric multidimensional scaling detected differences in environmental variables preference for both diploid and triploid forms. These finding indicate specific spatial and temporal microhabitat preference for diploid (sexual donors) and triploid (asexuals) C. elongatoides × C. tanaitica when coexisting as mixed a population.

In the Czech Republic, the Balkan spiny loach Sabanejewia balcanica was historically only known from the River Becva, a left tributary of the River Morava, itself a main tributary of the River Danube. Following its assumed extinction in the Czech Republic, a small population was found in a 1 km stretch of the River Vlara at the Slovak border, with individuals presumably having migrated from Slovakia. In 2016, we recorded six individuals in the downstream stretch of the River Jihlava. Based on present knowledge, this appears to be a population situated wholly outside of its previously known area of distribution, and the only population presently found in the 26000 km2 River Morava drainage basin. The distance of this population from the species' present distribution area and historic findings in the River Becva clearly indicate a much wider historical distribution of this species in the past.

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. Materials 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.

Cyprinus carpio is a commercially important fish in the aquaculture of the Czech Republic, while Carassius gibelio is an invasive species combining sexual and gynogenetic reproduction and often entering breeding ponds. The occurrence of F1 hybrids of these two phylogenetically closely-related fish has recently been reported. The objective of this study was to investigate selected aspects of physiology, immunity and blood biochemistry (i.e. parameters reflecting health status and condition) in both parental species and their F1 hybrids, all of the same age. The morphology was intermediate between parental species. The majority of biochemical, physiological and immune parameters were primarily affected by sampling period. For these parameters, hybrids achieved an intermediate character between parental species, but for biochemical and immune parameters they were still more similar to common carp, i.e. the species in the paternal position. The intermediate glucose and cholesterol levels together with the intermediate intestine–body size index in hybrids suggest the role of genetic introgression in determining the range of food utilizable for C. carpio × C. gibelio hybrids as well as their nutritional status, metabolic activity, and energy intake. In spring, females of gibel carp and hybrids reached higher GSI when compared to common carp; however, no spring increase in calcium (important for egg development) was found in hybrid females. Leukocyte count and complement activity in hybrids were intermediate between parental species. IgM level was significantly higher in females in both sampling periods, probably reflecting the different costs of reproductive investment between genders. We propose that the intermediality of traits associated with health and condition status in hybrids resulting from genetic introgression may potentially represent some advantage for hybrid vigor. Our results also highlight the good condition status of C. gibelio and may indicate a potential risk of competition between this invasive species and the economically important C. carpio in breeding ponds.

Brook trout (Salvelinus fontinalis) is a species of fish native to North-East America. Brook trout are also commercially raised in large numbers for food production. Skin infection and/or parasite outbreaks can have a serious economics effect on aquaculture businesses. For this reason, it has been hybridized with the more resistant Arctic char (Salvelinus alpinus). The aim of this study was an examination of the epidermal structure and dynamic in brook trout and its Arctic char hybrid which is less sensitive to skin infection. The samples of fish (72 brook trout, 72 brook trout × Arctic char hybrid) from fish farm in Pravíkov (49°19’10”N, 15°5’40”E) were collected five times during the year 2011. Absolute and relative epidermal thickness (in relation to body size) and relative proportion of secretory cells in a given volume of epidermis were measured. The epidermis structure of brook trout and brook trout × Arctic char hybrid both display similar seasonal dynamics, with a decrease in absolute and relative epidermal thickness and a reduction in the relative percentage of mucous secretory cells over the summer. On the other hand, the lower absolute (mean 103 µm (range 84–146 µm) in brook trout; 88 µm (range 68–115 µm) in hybrids) and relative epidermal thickness (mean 4.8 (range 3.6–6.8) in brook trout; 4.4 (range 2.9–6.4) in hybrids) and lower volume of secretory cells was observed to the hybrid (mean 28% (range 19–33%) in brook trout; 23% (range 10–30%) in hybrids). It can interrelate with their higher resistance to infection and/or parasite outbreaks.

Efforts to positively influence ecological processes and water quality by manipulating the fish community (biomanipulation) are of particular importance in drinking water reservoirs. One of the principle measures employed is to increase the abundance of predatory fish species as a means of reducing planktonophagous and benthophagous cyprinids. However, there is little information available on the effectiveness of different predatory fish in biomanipulation exercises. We examined the diet of the five dominant predatory species (pike Esox lucius, zander Sander lucioperca, asp Leuciscus aspius, European catfish Silurus glanis, and perch Perca fluviatilis) in five representative reservoirs in the Morava River drainage basin (Czech Republic). Fish prey made up 75 % of total food intake, with undesirable small cyprinids dominant by biomass (40 %). European catfish and asp were not taken as prey and showed no sign of cannibalism. On the other hand, predation on conspecific predatory species (including cannibalism) was relatively high in perch, pike and zander, thereby reducing their net benefit overall. This little-considered aspect of predatory feeding needs to be taken into consideration in future biomanipulation stocking strategies.

Summary Sculpins occasionally form interspecific hybrids in areas of mutual contact. These can be verified genetically and, potentially, morphologically. At the study site (Svratka River, Czech Republic), Cottus gobio are common whereas C. poecilopus represent a geographically isolated alien population. Potential hybrids between these two species were compared with the parent populations to establish simple identification criteria. Analysis of nuclear and mitochondrial DNA confirmed the existence of a new European hybridisation zone. Hybrids were the result of unidirectional crossing, with female C. gobio taking the maternal position. With the exception of the lateral line position, morphometric characteristics and the epidermis structure were similar in many traits, reflecting the contribution of both species, as well as in the number of sacciform cells where hybrids were similar to C. poecilopus. The vertical position of the lateral line allows recognition of hybrids directly in the field, a useful feature for future studies. The occurrence of these hybrids confirms expansion of non-native C. poecilopus at the expense of native C. gobio in rivers under anthropogenic pressure.

The epidermis structure of the studied specimens of Cottus gobio and C. poecilopus from the Morava watershed showed important differences. We noted a lower number of sacciform secretory cells in C. gobio, and also differences in relation to reproductive activity (the decrease in the number of secretory cells during the spawning period in both species). Significant differences were found in the erythrocyte count (1.90 ± 0.15 T.l-1 in C. gobio and 1.57 ± 0.07 T.l-1 in C. poecilopus), whereas the leucocyte count did not differ. A three-day-long exposure in higher temperature and lower oxygen saturated water conditions caused a marked increase in both blood parameters. These differences can be related to the distant physiological and ethological requirements of the species.

Summary This study describes the length-weight relationship of pure diploid individuals of Cobitis elongatoides from the Nova Řise Reservoir, Czech Republic. The resultant length-weight relationship was highly dependent on the individuals included, thus the length-weight relationship of males, small females and large females differed significantly. Furthermore, these relationships varied between sampling seasons. Further studies are planned to test for differences between different ploidy levels.

Carassius auratus gibelio is considered an alien fish species in the hydrographic system of the Czech Republic. Around 1976, this form immigrated from the River Danube into the confluence of the Morava and Dyje rivers and gradually spread over the hydrographic network over the course of the next 15 to 20 years. Helped by man, this species overcame the boundaries between particular drainage areas, expanding its range and colonising suitable habitats. C. a. gibelio has become fully naturalised and has produced numerous stable populations. This is the only non-indigenous fish species in the Czech Republic showing distinct characteristics of an invasive taxon. Initial populations of C. a. gibelio colonising the new area consisted solely of triploid females. The occurrence of males after 1990 started a process of transformation of the originally monosexual female (triploid) population into a mixed population containing both females and males. At present, males are predominantly diploid, with occasional triploid individuals. Females are predominantly triploid and less frequently diploid. Tetraploid individuals are quite rare. At the Morava-Dyje confluence, the population reproduces both gynogenetically and sexually. C. a. gibelio exerts important competitive, as well as destructive, effects upon the indigenous ichthyofauna. Native species of Carassius carassius and Tinca tinca, previously abundant have vanished from those localities dominated by C. a. gibelio. C. a. gibelio is fished for on hook and line in natural habitats in the Czech Republic, with an annual recorded catch of 25–50 t. Annual production in fishponds varies between 15 and 70 t, yet its marketable utilization is problematic.

Wild-captured 16 diploid, five triploid and one tetraploid Prussian carp Carassius gibelio males produced motile haploid, aneuploid (1·5n) and haploid to aneuploid (> 2n) sperm, respectively, in similar concentration and with the lowest percentage of live spermatozoa in sperm for the tetraploid male (mean ±s.d. 83·03 ± 1·76%; P 0·05).

Morphometric and genetic variation were examined in parental Carassius auratus gibelio and Carassius carassius individuals, and their natural hybrids. Of meristic traits, only the number of gill rakers clearly distinguished hybrids (39·4 ± 1·4) from parental C. a. gibelio (48·3 ± 0·7) and C. carassius (28·6 ± 1·1). MtDNA sequences showed that the hybrids were descendants of female C. a. gibelio. Microsatellite analysis confirmed the presence in hybrids of variants typical of C. a. gibelio and C. carassius.

A Carassius auratus complex from an artificial wetland in the Morava River basin is composed of triploid females. Based on body depth, sampled females could be divided into two groups: (i) high-dorsal (42.5% of standard length); and (ii) low-dorsal (36.1% of standard length). Both groups differed also in number of gill rakers (50.2 versus 45.4, respectively). In concordance with morphological differences, genetic analysis proved the existence of two haplotypes in examined individuals. The first haplotype is bound to the high-dorsal form with higher number of gill rakers. This is the most frequent haplotype in populations of the C. a gibelio form in the Czech Republic. The second haplotype is characteristic of the low-dorsal form with a lower number of gill rakers. This haplotype is close to haplotypes described in the C. a. langsdorfii form, which is known from Japan. and its occurrence within haplotypes specified in European territory is sporadic.

The karyotype of Zingel zingel from the Morava River (Czech Republic) was analyzed. The diploid chromosome number was 2n=48 in females and 2n=47 in males, however, one large unpaired metacentric chromosome was present in males. This proves to be the X1X1X2X2/X1X2Y multiple sex chromosome system developed from the fusion of two sub- or acrocentric chromosomes where a sex chromosome Y was present as one of them.

Gill characteristics and the size and number of erythrocytes were observed for three species of goby: Neogobius melanostomus, N. fluviatilis and N. kessleri. While erythrocyte size was similar in all species, N. fluviatilis had a statistically higher erythrocyte count. Significant differences were found in gill apparatus structure, with N. melanostomus having 25% and 50% greater gill contact area than N. kessleri and N. fluviatilis, respectively. Secretory goblet cells, which produce a protective mucous, were also present in highest numbers in N. melanostomus gill tissues. These physiological and morphological differences may be one reason for differences observed in the invasiveness of these three species.

The phylogenetic relationships and taxonomy of the spirlins in the genus Alburnoides are examined by comparative sequencing analysis of mitochondrial and nuclear markers. Molecular analyses revealed 17 Eurasian lineages divided into two main clades, termed the Ponto-Caspian and European in accordance with the lineage distribution. The indel diagnostics of β-actin and S7 markers and translation of cyt b to the amino acid chain were evaluated as a reliable identifying tool for most of the recognised lineages. Lineage richness is closely connected with the existence of known glacial refugia in most cases. The underestimation of species richness in the genus Alburnoides is confirmed: the genetic analyses support the validity of 11 morphologically accepted species; apart from them, four phylogenetic lineages requiring descriptions as separate species were revealed. The distribution area of the nominotypical species A. bipunctatus s. stricto is newly defined. Two diverging phylogenetic lineages, A. ohridanus, and A. prespensis complex, were observed in the Southeast Adriatic Freshwater Ecoregion, confirmed as a hotspot of endemic biodiversity. A. ohridanus demonstrates high divergence from the A. prespensis complex, represented by three similar mitochondrial lineages with the same nuclear haplotypes and sympatric occurrence. The range restricted endemism was confirmed for at least seven species. The Albanian river systems, as well as the wider Ponto-Caspian basin exhibit complications among definite species delineations and gaps in understanding of microevolutionary processes; these areas require further investigations.

Vete‰nik L., K. Halaaka, V. Luskova, S. Lusk: Erythrocyte Profile of Diploid and Triploid Silver Crucian Carp (Carassius auratus). Acta Vet. Brno 2006, 75: 203-207. Haematological analysis was performed on 27 adult specimens of Carassius auratus irrespective of sex in 2003 and on 32 juveniles of distinguished sex in 2004. In this study we found that the ploidy level affected significantly (p < 0.01) the values of the erythrocyte count, mean corpuscular volume and mean corpuscular haemoglobin. Although we did not prove any significant effect of sex in juvenile diploids of C. auratus on the values of erythrocyte profile, the erythrocyte count, haematocrit value and haemoglobin content value were higher for males than for females. The erythrocyte count decreased significantly (p < 0.01) with increasing ploidy level. The index of haemoglobin content followed the same trend of a decreasing mean value with increasing ploidy level. Mean corpuscular volume and mean corpuscular haemoglobin increased with the increasing ploidy level (p < 0.01). Haematocrit value and mean corpuscular haemoglobin concentration did not significantly differ from the point of view of the ploidy level.

Changes in the ichthyocenosis of five smaller streams of 2nd to 4th order existing in the spring section of the River Odra (Oder) catchment area, in the territory of the Czech Republic, were observed before and after the catastrophic floods of July 1997. Quantitative catches using electro-fishing were performed in June, August, and September 1997, i.e. a month before and 2 months after the floods. The maximum flow of water in the examined sites usually reached or exceeded the limit of the so-called ȁ8once in a century high waterȁ9. Extreme floods did not influence statistically the proven average readings of species diversity of ichthyocenosis in the examined sites (p = 0.5625), species variety (p = 0.7316), abundance per hectare (p = 0.3125), and biomass per hectare (p = 0.4375). A distinctive decline in abundance and also in the biomass of the ichthyocenosis took place in geomorphic reaches. Significant incisions and alterations in the routes of the streams were also observed. Statistical data of catches of key reophilous fish species from the River Oder catchment basin, all of which were affected by the floods, in the periods 1995–1996, 1997, and 1998–1999, were evaluated. Catches of the species of Salmo trutta and Thymallus thymallus in 1997 considerably increased. Only Thymallus thymallus experienced a more pronounced decrease in the years after the floods, when compared with the average readings made in the period 1995–1996. The readings of the adult abundance of Barbus barbus and Chondrostoma nasus did not prove a negative impact of the floods on the adult population of both species in the assessed years. Our findings suggest that the original fish communities may be naturally well adapted to culmination flows.

BackgroundCarassius auratus complexis an extraordinary species complex including the diploid and polyploid forms exhibiting asexual and sexual reproduction modes. The coexistence of both forms in the same habitats is currently reported. The stable coexistence of asexual and sexual forms assumes some disadvantages for asexuals that balance the costs of sex. In our study, we hypothesized and tested the differences in physiological (including heamatological and immunological), growth-related, condition-related, and fitness-related traits between gynogenetic females and sexuals.ResultsOur results revealed similar growth performance in gynogenetic females and sexuals measured by body size and weight, or expressed by condition factor. The energy allocation in reproduction measured by the relative size of gonads revealed no difference between gynogenetic and sexual females; in addition, both females in spawning expressed the same estradiol levels in blood plasma. We found a gender specific trade-off between investment in reproduction and immunocompetence (measured by the spleen-somatic index). Higher aerobic performance expressed by the heart index and higher oxygen-carrying capacity were found in sexual males, with increasing values before and during spawning. Our study evidenced significantly lower aerobic performance but higher oxygen-carrying capacity per erythrocyte in gynogenetic females when compared to sexuals. IgM production differed between gynogens and sexuals ofC. auratuscomplex.ConclusionsOur study indicates that a similar amount of energy is invested by both gynogenetic and sexual females ofC. auratuscomplex in reproductive behaviour. We suggest that lower aerobic performance in gynogens may represent their physiological disadvantage balancing the cost of sexual reproduction. A trade-off between the number of erythrocytes and the oxygen-carrying capacity per erythrocyte in sexual males and gynogenetic females may contribute to the coexistence of gynogenetic and sexual forms. In addition, the differences in specific immunity between gynogens and sexuals may also reduce the evolutionary disadvantage of sexual reproduction. In conclusion, we propose that several mechanisms contribute to the coexistence of the gynogenetic-sexualC. auratuscomplex.

Canalization of the lower reaches of the River Dyje included the isolation of its meanders. One of these meander lakes remained connected at its downstream end with the River Dyje at river kilometre (r. km) 4.44. The meander lake was 500 m long, with a width varying from 30 to 50 m, and a surface area of 1.2-2.0 ha depending on the water level in the river. In 1997-1999 we studied the temporal changes in the species composition of the fish stock, using gill nets and electrofishing. We found 38 fish species in the backwater under study. Cyprinid fishes were most common, especially Rutilus rutilus, Alburnus alburnus, Abramis brama, A. ballerus, Blicca bjoerkna, Carassius auratus. We also caught rare species such as Abramis sapa, Pelecus cultratus and Gymnocephalus schraetser, or species new to the Czech Republic, Sander volgense, Gymnocephalus baloni and Proterorhinus marmoratus. In addition to the cyprinid species mentioned above, we also found Esox lucius, Sander lucioperca, Perca fluviatilis and Gymnocephalus cernuus spawning in the backwater. There was also a permanent population of Cobitis elongatoides. The fish stock in the backwater was highly variable. Species diversity, size structure and abundance varied over the course of the year. It was markedly affected by the water discharge in the River Dyje. The results obtained document the importance of river backwaters for the fish communities inhabiting the river channel.

The skin histology from the Danubian spined loach Cobitis elongatoides disputes the notion that the spawning marks (lighter spots on the body sides of the females) are the result of physical damage to the epidermis by a male during spawning. Physiological changes that induce a specific local decrease in lateral pigmentation in some individuals appear to be a more likely source.

Despite being genetically very closely related, the marble trout Salmo marmoratus and the brown trout Salmo trutta exhibit marked phenotypic differences, particularly with regard to skin pigmentation. Histological analysis of skin from the head and gill cover of differently aged individuals of the two species was carried out in order to characterize differences in skin structure. The basic structure of skin of the individuals studied corresponded with that described for other salmonids, though the head epidermis was somewhat thicker in S. marmoratus than in S. trutta, thickening with age in both species. Numerous secretory goblet cells and sporadic secretory sacciform cells were observed in the upper and middle part of the epidermis in both species. Melanophores were present in both species only in the dermis, and were bigger in S. marmoratus and present at lower average density than in S. trutta, and more or less constant across all age classes. In adult S. marmoratus with fully established marble pigmentation, light areas at low density with small (i.e. aggregated) melanophores were present, while in S. trutta melanophores were more uniformly distributed.

The basic biochemical profile of gibel carp (Carassius gibelio), diploid–triploid cyprinid species complex with dual reproduction modes, was investigated. The aim of the study was to test for the effect of fish group (which combines the effects of ploidy and sex) and temporal changes on indicators of the biochemical profile of blood in gibel carp. We showed that the basic biochemical profile of blood is significantly influenced by season and fish group. Triploid gynogenetic females had a better condition measured by total protein concentration than sexual diploids. The higher concentrations of triacylglycerols and cholesterol in triploid females when compared to diploids indicate a higher metabolic rate and higher energy intake during the whole year, which may represent a disadvantage for triploids. Differences in the concentrations of blood biochemical analytes between triploid females and diploids suggest a potential difference in the regulation of a wide range of physiological and biochemical processes in which these analytes participate. The biochemical profiles of two forms of C. gibelio could at least partially explain the changes of character of its naturally occurring populations.

P. Abelló ...et al.-- 3 pages, 1 table, This article documents the addition of 123 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Brenthis ino, Cichla orinocensis, Cichla temensis, Epinephelus striatus, Gobio gobio, Liocarcinus depurator, Macrolophus pygmaeus, Monilinia vaccinii-corymbosi, Pelochelys cantorii, Philotrypesis josephi, Romanogobio vladykovi, Takydromus luyeanus and Takydromus viridipunctatus. These loci were cross-tested on the following species: Cichla intermedia, Cichla ocellaris, Cichla pinima, Epinephelus acanthistius, Gobio carpathicus, Gobio obtusirostris, Gobio sp. 1, Gobio volgensis, Macrolophus costalis, Macrolophus melanotoma, Macrolophus pygmaeus, Romanogobio albipinnatus, Romanogobio banaticus, Romanogobio belingi, Romanogobio kesslerii, Romanogobio parvus, Romanogobio pentatrichus, Romanogobio uranoscopus, Takydromus formosanus, Takydromus hsuehshanesis and Takydromus stejnegeri

A reduction of epidermal club cells and an increase of goblet cells were found in Carassius gibelio during spawning when compared to postspawning. A significantly lower proportion of club cells at spawning was found in diploid males and triploid females than in diploid females. It could be linked to male efforts to avoid a fright reaction and the potential adoption of this strategy by gynogenetic females, or alternatively to a higher parasite infection or immunosuppression during spawning.

Morphological (meristic and morphometric traits), karyological and molecular (microsatellites, cytochrome b) analyses were performed to characterize a hybrid of the roach Rutilus rutilus and nase Chondrostoma nasus. Meristic and morphometric traits were different between hybrid and both parental species. The number of chromosomes found in hybrid specimen indicated that this individual represents the post-F(1) generation of hybrids and the microsatellite analysis of the hybrid showed the presence of variants typical for R. rutilus and C. nasus.

The phylogenetic relationships among gudgeons that represent most nominal taxa within Gobio gobio sensu lato were examined by mitochondrial and nuclear genome sequencing. The molecular analyses confirmed the separate generic status of Gobio as a monophyletic group and revealed 15 Eurasian lineages divided into two main clades, the Northern European and the Ponto-Caspian. The validity of eleven nominal taxa as distinct species was confirmed, gudgeons from the Volga River basin were described as a new species G. volgensis, and three revealed phylogenetic lineages were submitted for a comprehensive revision as "species-in-waiting". The species G. gobio showed a wide range extending from the British Isles to the Black Sea coast and overlapped the areas of several other species. Four pure lineages were detected in the middle Danube River basin. The Crimean Peninsula was found to be a region with the occurrence of individuals of hybrid origin. This region will require special investigation to define species participating in hybridization events, and to establish further steps for the conservation of endemic native gudgeon species. A simple diagnostic method, based on different lengths of the PCR products, called "S7indel diagnostics" is presented for further taxonomic investigations in the genus Gobio.

The effect of water temperature and flow on the migration of fish was observed using weekly inspections of a fishpass on the lowland section of the River Elbe (Střekov, Czech Republic) from spring to fall 2003 and 2004. The effect was examined separately for immature (up to 2 years old) and adult fish and also the most abundant species (roach Rutilus rutilus, bleak Alburnus alburnus, chub Squalius cephalus, gudgeon Gobio gobio). More than 13 thousand fish from 23 species were recorded in the fishpass during both years. The highest levels of fish occurrence in the fishpass were observed during the spring spawning migrations of adults (April–May) as well as during the late summer and fall migrations of adult and immature fish (September–November). While the total number of both fish age categories was significantly related to the interaction of water temperature and flow, however, responses of individual species and age categories differed from each other. The numbers of adult bleak, chub and gudgeon increased with higher temperature. The maximum numbers of adult bleak migrated at medium values of temperature (15–20 °C) and flow (140–270 m3 s-1). The abundances of adult chub and adult plus immature gudgeon were higher with higher flow. The numbers of immature bleak and chub decreased with increasing flow. The numbers of adult and immature roach were influenced only by water flow with maximal numbers migrating under medium values of flow. Generally, we observed that immature fish and small- and middle-sized species required lower values of water flow than adult fish or large species to facilitate their movement. The exception was gudgeon, which required higher values of flow for its migration, a feature that could be related to its bottom dwelling nature or rheophily.