Mitochondrial DNA variation in European populations of Silurus glanis

Mitochondrial DNA diversity of 13 wild Silurus glanis populations (covering the entire range of the species) and eight hatchery populations was investigated. PCR-RFLP analysis of four regions of mitochondrial DNA (cytochrome b, control region, ND-5/6) was used. Nineteen haplotypes were found. Thirteen of them were private. The proportion of total genetic diversity attributable to population differentiation was almost 80%. Despite the existence of significant differentiation between populations for mtDNA variation, no consistent pattern of geographic structuring was revealed and nucleotide divergence among S. glanis populations was low. These phenomena are discussed with regard to the impact of glaciation events. The domesticated stocks show less genetic diversity than natural ones, possibly due to their mode of management. Analysis of three European catfish species S. glanis, S. aristotelis and Silurus triostegus (sampled in the Euphrates river) revealed several endonucleases which produced restriction phenotypes diagnostic for the three species.     

Reduced genetic diversity and low effective size in peripheral northern European catfish Silurus glanis populations

Using 10 polymorphic microsatellites and 1251 individual samples (some dating back to the early 1980s), genetic structure and effective population size in all native and introduced Swedish populations of the European wels catfish or Silurus glanis were studied. Levels of genetic variability and phylogeographic relationships were compared with data from a previous study of populations in other parts of Europe. The genetically distinct Swedish populations displayed comparably low levels of genetic variability and according to one-sample estimates based on linkage disequilibrium and sib ship-reconstruction, current local effective population sizes were lower than minimum levels recommended for short-term genetic conservation. In line with a previous suggestion of postglacial colonisation from a single refugium, all Swedish populations were assembled on a common branch in a star-shaped dendrogram together with other European populations. Two distinct subpopulations were detected in upper and lower habitats of River Emån, indicating that even minor dispersal barriers may restrict gene flow for wels in running waters. Genetic assignment of specimens encountered in the brackish Baltic Sea and in lakes where the species does not occur naturally indicated presence of long-distance sea dispersal and confirmed unauthorised translocations, respectively.     

Development of microsatellite markers for southern catfish (Silurus meriaionalis) and cross‐species amplification in northern sheatfish (Silurus soldatovi)

Forty microsatellite markers were developed from a (CA)_n enrichment library created from the DNA of southern catfish (Silurus meriaionalis). Also, the population structure of northern sheatfish (Silurus soldatovi) was examined by 24 microsatellite loci. They are polymorphic in at least one of the two geographically distant populations sampled from the Heilongjiang River and the Songhuajiang River in North China, respectively. Unbiased expected heterozygosity levels varied from 0.435 to 0.946 and number of alleles per locus varied from three to 20. Results indicated that these microsatellite loci were highly polymorphic and could be used as genetic markers.     

A study of a polymorphic globulin in the serum of Silurus glanis L.

A polymorphism of S-globulin was detected in serum of Silurus glanis L. by starch gel electrophoresis. Three phenotypes were observed which are apparently controlled by two codominant alleles, Sg^A and Sg^B , of an autosomal locus, Sg . Although on electrophoresis S-globulin and transferrin have similar mobilities, the properties of the two proteins differ.     

Resistance of the European catfish (Silurus glanis) to channel catfish virus

European catfish (Silurus glanis) fingerlings (2 to 4 g each) were tested for susceptibility to channel catfish virus (CCV). They had supported CCV replication at 2 days after intraperitoneal injection with 0.1 ml of saline containing 10⁵ TCID₅₀. Homogenized visceral organs (liver, kidney and spleen) contained 10⁴ TCID₅₀/0.1 ml at 2 days post inoculation (PI) but at 4 days the titer decreased to 10¹ TCID₅₀. Bathing European catfish in CCV yielded only one positive sample with à titer of 10^0.83 TCID₅₀ per 0.1 ml of tissue. No clinical signs of CCV developed and no virus related deaths occurred.     

Chromosomal and morphological abnormalities caused by oocyte ageing in Silurus glanis

The effects of ageing oocytes for 6 h before fertilization in the European catfish Silurus glanis are compared with the same experiment under normal conditions (stripping and fertilization immediately after ovulation). Fertilization rate and hatching rate are lower in the aged groups, while the percentages of malformed larvae and chromosomal abnormalities are significantly higher. Several kinds of abnormalities are described in detail.     

Chromosome banding study of European catfish,Silurus glanis (Pisces,Siluridae)

The karyotype of European catfish (Silurus glanis L.) was analyzed sequentially by means of silver staining and the chromomycin A₃ (CMA₃)/distamycin A (DA)/DAPI fluorescence technique and by C-banding, respectively. The nucleolus organizer regions (NORs) were localized on the submetacentric pair No. 14. Brilliant CMA₃ fluorescent heterochromatin blocks corresponded to the NORs visualized by silver staining. No DA/DAPI-bright positive fluorescent patterns were detected while C-banding led to the detection of specific banding patterns on several chromosome pairs.—Using these banding data, the karyotype of S. glanis was redescribed.     

Age and growth of the European catfish (Silurus glanis) in a Turkish Reservoir and comparison with introduced populations

The European catfish, Silurus glanis, is native to eastern Europe and western Asia and is among the largest freshwater fish in the world. Despite its increasing economic importance and its frequent introductions, the ecology and life-history of this species is poorly known due to the difficulty of sampling such a large species in large rivers and standing waters. Our study provides the first data on age and growth of this species in Turkish waters, where it is native. We report the length-weight relationships and age and size structure of this population, which were significantly different between females and males. A marginal increment analysis indicated that annulus formation occurred between May and June. The estimates of three growth functions (von Bertalanffy, logistic and Gompertz) are reported, with the von Bertalanffy growth providing a better fit and more realistic parameter estimates. Growth rates were significantly higher in males than in females and were overall higher compared to other native populations but similar to introduced populations of similar latitude.     

Genetic structure of Eurasian badgers Meles meles (Carnivora: Mustelidae) and the colonization history of Ireland

The present study examined the contemporary genetic composition of the Eurasian badger, Meles meles, in Ireland, Britain and Western Europe, using six nuclear microsatellite loci and a 215‐bp fragment of the mitochondrial DNA control region. Significant population structure was evident within Europe (global multilocus microsatellite F_ST = 0.205, P < 0.001; global mitochondrial control region Φ_ST = 0.399, P < 0.001). Microsatellite‐based cluster analyses detected one population in Ireland, whereas badgers from Britain could be subdivided into several populations. Excluding the island populations of Ireland and Britain, badgers from Western Europe showed further structuring, with evidence of discrete Scandinavian, Central European, and Spanish populations. Mitochondrial DNA cluster analysis grouped the Irish population with Scandinavia and Spain, whereas the majority of British haplotypes grouped with those from Central Europe. The findings of the present study suggest that British and Irish badger populations colonized from different refugial areas, or that there were different waves of colonization from the source population. There are indications for the presence of an Atlantic fringe element, which has been seen in other Irish species. We discuss the results in light of the controversy about natural versus human‐mediated introductions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Efficacy of tagging European catfish Silurus glanis (L., 1758) released into ponds

The efficacy and sub‐lethal consequences of single and double tagging European catfish Silurus glanis with Petersen disc and passive integrated transponder (PIT) tags were examined in short (laboratory) and longer‐term (field) experiments. Tag retention in the laboratory was 100%, with normal behaviour (i.e. feeding) in all fish returning within 36 h. In the field, 65 of 120 tagged S. glanis were recaptured from five small study ponds, with 85% retaining their PIT tags, though recapture rates and tagging efficacy were highly variable amongst locations. This is consistent with literature for other fishes, suggesting that tagging efficiency is variable across species and largely context dependent (fish length, tagging location, habitat).     

Mutual influence of protein and lipid feed content on European catfish (Silurus glanis) growth

We wished to determine protein and lipid content in pelleted raw fish food, necessary for optimal growth of European catfish (Silurus glanis). Experiments were set up in 20 cages, each holding 30 young catfish. Fishes in each cage received a different food combination over a 98‐day period at favourable physical and chemical water conditions. Food protein content varied between 37.5 and 45%, while lipid content, added in the form of soybean oil, varied between 3 and 11%. The oil contained an adequate ω‐fatty acids concentration, necessary for fish growth. The main growth indicators determined at the end of experiment were total body gain, specific growth rate and feed conversion ratio. There was a high statistical difference among the experimental groups receiving variable food combinations for each growth parameter (P < 0.001). Both protein and lipid food content affected growth parameters, but in a different manner. Further analysis – percentage of change depending on lipid to protein ratio and bivariate surface analysis – allowed us to recognize the most economical combination: 39.5% protein + 9% lipid content. The addition of 9% soybean oil to the fish food reduces the necessary protein concentration by 5.5%, with resulting identical catfish growth effects.     

Cryopreservation of European catfish Silurus glanis sperm: sperm motility, viability, and hatching success of embryos

The aim of this study was to elaborate cryopreservation methods for ex situ conservation of European catfish. The success of sperm cryopreservation was evaluated by post-thaw sperm motility and velocity, percentage of live spermatozoa and fertility (hatching rates) using frozen/thawed sperm. The best hatching rates of 82-86% were obtained with sperm stored for 5 h before freezing in immobilizing solution and frozen with Me2SO in concentrations of 8, 10, and 12%, or with a mixture of 5% Me2SO and 5% propandiole. These results did not significantly differ from the fresh sperm control sample. The percentage of live spermatozoa in frozen/thawed sperm did not correlate with hatching rate or motility of spermatozoa, but was negatively correlated with velocity of spermatozoa (r=-0.47, P=0.05). The percentage motility in frozen/thawed sperm ranged from 8 to 62%, when sperm was stored in immobilizing solution 5h before freezing. The average value in the fresh sperm (control) was 96%. The frozen/thawed sperm motility rate significantly correlated with the hatching rate (r=0.76, P=0.0002), but not with the percentage of live spermatozoa (r=0.16, P=0.52) or the sperm velocity (r=0.07, P=0.79). The velocity of frozen/thawed spermatozoa ranged from 37 to 85 microm/s, whereby methanol concentrations of 7.5 and 10% resulted in highest velocities. Freezing sperm volumes of 1-4 ml did not affect the quality of frozen/thawed sperm.     

Genetic structure in Orchesella cincta (Collembola): strong subdivision of European populations inferred from mtDNA and AFLP markers

Population genetic structure is determined both by current processes and historical events. Current processes include gene flow, which is largely influenced by the migration capacity of a species. Historical events are, for example, glaciation periods, which have had a major impact on the distribution of many species. Species with a low capacity or tendency to move about or disperse often exhibit clear spatial genetic structures, whereas mobile species mostly show less spatial genetic differentiation. In this paper we report on the genetic structure of a small, wingless arthropod species (Orchesella cincta: Collembola) in Europe. For this purpose we used mtDNA COII sequences and AFLP markers. We show that large genetic differences exist between populations of O. cincta, as expected from O. cincta's winglessness and sedentary lifestyle. Despite the fact that most variability was observed within populations (59%), a highly significant amount of AFLP variation (25%) was observed between populations from northwestern Europe, central Europe and Italy. This suggests that gene flow among regions is extremely low, which is additionally supported by the lack of shared mtDNA alleles between regions. Based on the genetic variation and sequence differences observed we conclude that the subdivision occurred long before the last glaciation periods. Although the populations still interbreed in the lab, we assume that in the long term the genetic isolation of these regions may lead to speciation processes.     

Comparison of methods for hatchery-scale triploidization of European catfish (Silurus glanis L.)

Heat-, cold- and hydrostatic pressure shocks were applied in order to improve triploidy induction in European catfish ( Silurus glanis L . ). A 41°C heat shock (45 s, starting 9 min after gamete activation) provided 88% triploids and a high percentage of malformation (38.8 ± 4.1%). The superior 6°C cold shock (20 min, starting 9 min after gamete activation) gave 100% triploids and a 33.4 ± 3.8% triploid yield. The earliest hydrostatic treatments (600 kg cm²), lasting 4 min and starting 3 min after gamete activation, gave 97.8 ± 1.8% triploids and a 33.7 ± 16.9% triploid yield. The ploidy level was investigated using four approaches: karyotyping, quantification of Ag-stained nucleoli per cell, flow cytometry, and erythrocyte nuclear sizing by computer-assisted image analysis. Induction of triploidy under mass conditions in three experiments gave triploid percentages of 74%, 83% and 66%. Five months later, the percentage of triploids significantly decreased to 12.4%, 8.2% and 21.4%. The growth performance of yearlings was better in diploids than in triploids. Differences between diploids and triploids were 13.5% (NS), 27.6% (P   < 0.001) and 25.4% (P   < 0.05) in the three experiments. Analysis of variance showed the influence of ploidy (P   < 0.001) on growth rate, and multiple range analysis (LSD) assessed differences between total diploids (12.6 g) and total triploids (9.5 g) at the P   < 0.01 level.     

东北大口鲇2个群体的微卫星DNA多态分析

利用磁珠富集法克隆制备的24个大口鲇（Silurus meriaionalis Chen）微卫星标记,对黑龙江野生群体与松花江养殖群体2个东北大口鲇（S．soldatovi）的地理种群的等位基因频率（P）、观测杂合度（Ho）、期望杂合度（He）、多态信息含量（PIC）和有效等位基因数（Ne）等进行了遗传检测,以遗传偏离指数（d）检验Hardy—Weinberg平衡,并以Nei氏遗传分化系数（GST）和AMOVA分析（ФST）群体遗传变异的来源。同时,使用PHYLIP3．63软件绘制基于Nei氏遗传距离的个体间UPGMA系统树。结果表明：24个微卫星标记在东北大口鲇的2个群体中共扩增出1357条多态性片段,片段长度为1024385bp,总体平均等位基因8．875个,可以用于东北大口鲇遗传多样性的评估。并发现8个可区分这2个种群的遗传标记;黑龙江群体的P、Ho、He、PIC和Ne依次为0．165、0．435、0．758、0．742和5．019,松花江群体为0．147、0．299、0．847、0．764和5．944,在这些多样性参数上,方差分析也显示2地理种群差异不显著,在大多数位点并无显著差异,仅HLJcf37位点具有显著差异：在多个位点偏离Hardy—Weinberg平衡,2群体呈现不同程度的杂合体过度,纯合体完全缺失现象,其原因有待证实;群体遗传变异分析证实2群体间遗传分化较弱,其98％以上的变异是由群体内个体间的遗传变异引起的,群体间的变异对总变异影响不显著。UPGMA系统树也显示出个体间遗传距离小,亲缘关系很近。结果表明,人工繁殖没有对东北大口鲇的遗传多样性产生影响,该种群遗传分化小,种质资源状况良好。     

Diel dualism in the energy consumption of the European catfish Silurus glanis

Twenty individuals of the largest European freshwater predator, the European catfish Silurus glanis, were tagged with electromyogram (EMG) physiological telemetry sensors. The fish were observed during diel cycles during the spring and summer in the Elbe and Berounka Rivers, Czech Republic. The purpose of this study was to determine whether diel dualism in the activity of S. glanis occurs naturally or is induced by the laboratory environment and by the conditions occurring in aquaculture. The results obtained from the riverine environment tended to show dualism in the use of the light and dark phases of the day because 35% of the individuals varied from a site‐specific common diel activity pattern. The EMG values increased in accordance with the mass (M) of the fish. To eliminate the influence of M on individual energy consumption, the EMG records were analysed in terms of the EMG:M ratios. High individual variability was found in these ratios. The diel activity pattern of the individuals with relatively high energy consumption differed from the common diel activity pattern. In contrast, the fish that adopted the common diel activity pattern displayed relatively low energy consumption. The results of this study indicated that dualism and energy consumption are related. The EMG values also varied with the values of the environmental variables. Increasing temperature was associated with high EMG values, whereas the EMG values decreased with increasing flow.     

Genetic differentiation of European grayling populations across the Main, Danube and Elbe drainages in Bavaria

Analysis of mitochondrial ( ND-1/3/4 genes) and nuclear ( GH-1 gene, four microsatellite loci) DNA markers of European grayling Thymallus thymallus populations identified strong genetic differentiation between the Rhine/Main, Elbe and Danube drainages in Bavaria, as a result of both present processes and past history. The Danube and the Main-Elbe group diverged about five times earlier than the populations of Main and Elbe. These data suggest that exchange and transfer of grayling stocking material between these drainages should be avoided, to maintain the genetic diversity and integrity of populations.     

Application of DNA metabarcoding on faeces to identify European catfish Silurus glanis diet

In this study, the results of conventional stomach‐content analysis are compared with the recent DNA metabarcoding approach on faeces to identify fish species consumed by non‐native European catfish Silurus glanis in the Garonne River (south‐western France), with a special emphasis on anadromous prey. Fourteen prey species were identified in the stomach contents or faeces, including four anadromous fish species. Despite higher intestine than stomach emptiness, more species were identified through faecal analysis (11 of 14) than through stomach‐content analysis (five of 14) suggesting that DNA metabarcoding on faeces is an efficient, non‐intrusive technique to study the diet of predatory fishes.     

Genetic variation and population structure in Scandinavian wolverine (Gulo gulo) populations

Wolverine (Gulo gulo) numbers in Scandinavia were significantly reduced during the early part of the century as a result of predator removal programmes and hunting. Protective legislation in both Sweden and Norway in the 1960s and 1970s has now resulted in increased wolverine densities in Scandinavia. We report here the development of 15 polymorphic microsatellite markers in wolverine and their use to examine the population sub-structure and genetic variability in free-ranging Scandinavian wolverine populations as well as in a sample of individuals collected before 1970. Significant subdivision between extant populations was discovered, in particular for the small and isolated population of southern Norway, which represents a recent recolonization. Overall genetic variability was found to be lower than previously reported for other mustelids, with only two to five alleles per locus and observed heterozygosities (H(O)) ranging from 0.269 to 0.376 across the examined populations, being lowest in southern Norway. Analysis of the mitochondrial DNA control region revealed no variation throughout the surveyed populations. As the historical sample did not show higher levels of genetic variability, our results are consistent with a reduction in the genetic variation in Scandinavian wolverines that pre-dates the demographic bottleneck observed during the last century. The observed subdivision between populations calls for management caution when issuing harvest quotas, especially for the geographically isolated south Norwegian population.