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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. [ABSTRACT FROM AUTHOR]

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.

Information about ploidy is important in both commercial and conservation aquaculture and fish research. Unfortunately, methods for its determination, such as karyology, determination of the amount of DNA in a cell using microdensitometry or flow cytometry and/or measuring erythrocytes in a blood smear can be stressful or even destructive. Some of these methods are also limited by the relatively large minimum size of the individual being measured. The aim of this study was to test a new low-stress method of determining ploidy by measuring the size of erythrocytes in the capillaries of a fish, including small individuals. First, we examined diploid and triploid loach (Cobitis sp.) and gibel carp, Carassius gibelio (Bloch, 1782), using flow cytometry and blood smears, with these results being used as a control. Subsequently, we measured the size of erythrocytes in the caudal fin capillaries of anesthetized fishes of known ploidy under a light microscope. For both the loaches and gibel carp, direct observation of the mean erythrocyte size in epithelial fin capillaries provided a consistent and reliable determination of ploidy when compared with the controls based on flow cytometry and blood smears. This new method allows for rapid determination of ploidy in living small fish, where collection of tissue using other methods may cause excessive stress or damage. The method outlined here simply requires the measurement of erythrocytes directly in the bloodstream of a live fish, thereby making it possible to determine ploidy without the need for blood sampling. The method described is sufficiently efficient, less demanding on equipment than many other procedures, can be used by relatively inexperienced personnel and has benefits as regards animal welfare, which is especially important for fish production facilities or when dealing with rare or endangered species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three species of loaches (Cobitis L., 1758) were collected and examined for endohelminths from North Bulgaria. The most common was the trematode Allocreadium transversale (Rudolphi, 1802), which is reported for the first time in Bulgaria. Measurements and figures as well as host-species and locality details are presented. Allocreadium transversale was recorded from all three loach species: Cobitis elongatoides, C. elongata and C. strumicae, the last two being new host records for A. transversale. In addition, metacercariae of Clinostomum complanatum (Rudolphi, 1814) and one unidentified nematode were found. The helminth fauna of loach was quite depauperate, the factors of which have to be elucidated. [ABSTRACT FROM AUTHOR]

While fish communities have been studied in Czech reservoirs for decades, monitoring has increased since implementation of the EU Water Framework Directive (2000 / 60 / EC). Despite this, many smaller drinking water reservoirs have yet to be surveyed. Between May and July 2016, we undertook a pilot-study examining the fish communities of five Moravian reservoirs (Ludkovice, Bojkovice, Hubenov, Nová Říše and Landštejn). Fish were sampled using boat electrofishing along the littoral zone and Nordic gill nets in the pelagic zone. Both methods were evaluated separately and combined as CPUE and relative abundance and biomass ( %). Nineteen fish species and one hybrid were recorded, with roach Rutilus rutilus dominating overall by abundance, but carp Cyprinus carpio, pike Esox lucius and wels Silurus glanis dominating by biomass in electrofishing samples. Predatory species represented up to 60 % of biomass in the combined sample, with an F / C index ranging from 0.5 - 3, implying a high abundance of predators. Electrofishing tended to underestimate the abundance of bleak and ruffe, while gill nets underestimated the biomass of predatory species. In some reservoirs, the abundance of pike and wels was high (though it is difficult to say if these fish were stocked or the result of natural reproduction). In others (e.g. Landštejn), zander Sander lucioperca were not registered by either sampling method, despite intensive stocking. Overall, gill netting alone appears inadequate for gaining a true picture of the fish community in reservoirs and we suggest a combination of electrofishing and gill netting in future. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the Czech Republic, the Balkan spiny loach Sabanejewia balcanica was historically only known from the River Bečva, 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 Vlára 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 Bečva clearly indicate a much wider historical distribution of this species in the past. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Carassius auratus complex is 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. Results: Our 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 of C. auratus complex. Conclusions: Our study indicates that a similar amount of energy is invested by both gynogenetic and sexual females of C. auratus complex 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-sexual C. auratus complex. [ABSTRACT FROM AUTHOR]

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 x 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 x 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 urn (range 84-146 urn) in brook trout; 88 urn (range 68-115 urn) 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article discusses the fish occurrence related to water temperature, fish size, and water flow on the lowland area in the fish pass of the River Elbe in Czech Republic in 2003-2004. It discusses the interaction of the fish species including roach, bleak, and gudgeon to the water temperature and flow. An overview of the rheophily of the fish or its bottom dwelling nature is also provided.

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. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article focuses on a study which tested the hypothesis that the appearance of spawning marks in Danubian spined loach Cobitis elongatoides females resulted from grazing by males while attached to the female. The study found that the average thickness of the outer layer of the integument is about 100 µ meter. The dermis of Cobitis elongatoides females contains scales that cause an undulation of the line between epidermis and dermis. Study authors concluded that the appearance of spawning marks in Cobitis elongatoides females is caused by physiological change sin female organism while spawning.