The influence of temperature on the growth of the European catfish (Silurus glanis L.)

The influence of temperature on growth, feed conversion, and protein and gross energy utilization was assessed in two experiments using the European catfish, Silurus glanis L. Animals of 55 g and 24 g were used in trials lasting 6 and 7 weeks, respectively. The optimum temperature for growth was within the range of 25 to 28°C, with the best results obtained at 27°C. Using à feed of low protein content (30.3%), a feed conversion of 1.67 was achieved at à specific growth rate of 1.78% of body weight/day.     

Purification and properties of serine proteinases from European catfish Silurus glanis L. pancreas

Three trypsin isoforms (designated as T1, T2, and T3), three chymotrypsin isoforms (Kh1, Kh2, and Kh3), and two elastase isoforms (E1 and E2) were isolated from the pancreas of European catfish Silurus glanis L. by salting out with (NH4)2SO4, gel chromatography on Sephadex G-75, and ion exchange chromatography on DEAE cellulose. Isoelectric points of the enzymes, determined by isoelectric focusing, amounted to 4.42 for T1, 5.64 for T2, 6.90 for T3, 4.93 for Khl, 5.23 for Kh2, 6.18 for Kh3, 6.17 for E1, and 8.48 for E2. Molecular weights of proteinases within each group were close and amounted to 30100 Da for trypsins, 39800 Da for chymotrypsins, and 24000 Da for elastases. The enzymes isolated displayed maximal activities at alkaline pH values. Inhibitor analysis demonstrated that all the proteinases isolated from European catfish pancreas belonged to the serine type.     

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.     

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.     

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.     

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.     

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).     

Linolenic acid supplementation in the diet of European catfish (Silurus glanis): effect on growth and fatty acid composition

In an 18‐week treatment, the effect of linolenic acid on European catfish (Silurus glanis L.) growth indicators was investigated as to weight gain, feeding coefficient (FCR value), specific growth rate (SGR value), protein efficiency ratio (PER value), productive protein value (PPV) and survival rate. Concurrently, the fishmeat chemical composition was also investigated. The experiment was organized into four groups, each divided into three subgroups. Stocked in each of 12 cages were 30 × 1‐year‐old catfish, with individual weights ranging from 148.5 to 151.5 g/ind. All fish were given standard feed for European catfish which contained 45% protein. The first batch, control group (C), received no additional linolenic acid. Linolenic acid was added to the feed of the second (E₁), third (E₂) and fourth group (E₃), at 0.5, 1.0 and 1.5%, respectively. Growth indicator improvement was best in the E₂ group fed the 1% linolenic acid, whereby the fish weight gain was 12.6% higher and the feeding coefficient 12.9% lower, while SGR, PER and PPV values were 6.1, 12.0 and 15.8% better than the control group. Growth indicators were also significantly (P < 0.01) improved in the three groups receiving additional linolenic acid in comparison to the control group. Moreover, this addition positively affected fishmeat quality by increasing meat protein content from 18.04% (C) to 18.79% (E₃). The total unsaturated fatty acid content also increased from 65.07% (C) to 69.82% (E₃), and the total saturated fatty acid content decreased from 31.36% (C) to 26.50% (E₃); consequently, the ratio of unsaturated to saturated fatty acids increased from 2.07% (C) to 2.63% (E₃). It can be concluded that the addition of 1% linolenic acid to standard catfish feed has beneficial effects on fish growth indicators and meat quality.     

Genetic structure and phylogeography of European catfish (Silurus glanis) populations

The genetic structure of Silurus glanis (Europe's largest freshwater fish species) across most of its natural distribution was investigated using 10 microsatellite loci. The revealed levels of genetic diversity were much higher than previous allozyme and restriction fragment length polymorphism mitochondrial DNA analyses had shown; relative levels of variability among populations were however, in good agreement with the previous studies. Populations from large basins (Volga and Danube rivers) were the most polymorphic, while samples from the smaller Greek rivers, which are more prone to genetic bottleneck, exhibited the lowest levels of genetic diversity. Microsatellite multilocus genotyping permitted the assignment of individual fish to their population of origin with a score as high as 98.3%. Despite the great genetic differentiation of S. glanis populations, no consistent pattern of geographical structuring was revealed, in contrast to previous studies of European freshwater fish species. A model of isolation by distance seems more probable and a hypothesis of recent dispersion from only one glacial refugium is proposed. The discovery of the highest levels of microsatellite and mitochondrial diversity in the Volga sample and the presence of river connections, during the Pleistocene, between this area and all major areas of the present catfish distribution, place this refugium around the Ponto-Caspian region. Combining these data with those from previous studies, a number of markers are now available to monitor wild and hatchery populations even at the individual level.     

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.     

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.     

Proteinases for the gastric mucosa of the European sheatfish, Silurus glanis L

Three proteinases named as P1, P2 and P3, were isolated from European sheatfish (Silurus glanis L.) gastric mucosa by salting-out of (NH4)2SO4, gel-chromatography on Sephadex G-75 and ion-exchange chromatography on DEAE-cellulose. Isoelectric points of isolated proteinases were determined by isoelectric focusing and were equal to 1.9, 3.2 and 4.75 respectively for P1, P2 and P3. The molecular weight of P1 was 39,800 Da and proteinases P2 and P3 had a molecular weight of 30,200 Da. The optimum pH for three peptidases isolated from sheatfish gastric mucosa and maximum stability of these enzymes were found at acidic pH. It allowed identifying these proteinases as pepsin-type enzymes of fish.     

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.     

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.     

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.     

Partial characterization of transferrins of catfish (Silurus glanis L.) and pike (Esox lucius L.)

Basic composition and properties of isolated transferrins of Silurus glanis and Esox lucius have been compared. In transferrin of S. glanis carbohydrate is absent, but it is present in transferrin of E. lucius (2.5%). The N-terminal amino acid is alanine in both species. Mol. wts are 68,400 (S. glanis) and 86,800 (E. lucius). Transferrins of the two species are heterogeneous, but genetic polymorphism was not observed.     

Explicit site fidelity of European catfish (Silurus glanis,L., 1758) to man‐made habitat in the River Meuse,Netherlands

After a century of near absence, records of European catfish (Silurus glanis, L., 1758) in the Netherlands have increased markedly since 1994. The majority of records (about 60% of the total) originate from a 12 km dammed section of the River Meuse in the province of Limburg. This paper reports on a study conducted to obtain information on the behaviour and habitat preferences of catfish at this location, whereby 20 adult Silurus glanis were implanted with both acoustic and transponder tags and their behavior monitored using a combination of passive and active methodologies. All fish remained within the study area and did not enter either the contiguous riverine sections or connected lakes. The catfish expressed schooling, nocturnal activity and strong site fidelity to a specific river section containing artificial habitat (in the form of moored boats) and were influenced by the presence and operation of nearby energy generation plants. The results are discussed in relation to the potential growth and dispersal of catfish populations and the extent to which anthropogenic activities (particularly energy generation schemes) at the site have inadvertently created favourable habitat that has assisted the colonization of catfish and impacted negatively on the wider fish community.