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.     

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.     

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.     

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.     

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.     

Shock-induced triploidy and its effect on growth and gonad development of the European catfish, Silurus glanis L.

Triloidy was induced in European catfish, Silurus glanis L., by cold-shocking eggs at 4°C for 30 and 40 min respectively, starting 5 min after fertilization. The hatching success of cold-shocked eggs was 25–30%. Cold shocks longer than 1 h caused total mortality. The triploid character of the cold-shocked European catfish was proved by karyological and red blood cell size analyses. The gonads of the triploid fish were significantly smaller than those of the diploids, while the growth rate values of the triploids were significantly higher than those of the diploids.     

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.     

Electron microscopic demonstration of lectin binding sites in the taste buds of the European catfish Silurus glanis (Teleostei)

Summary Taste buds in the European catfish Silurus glanis were examined with electron microscopic lectin histochemistry. For detection of carbohydrate residues in sensory cells and adjacent epithelial cells, gold-, ferritin-and biotin-labeled lectins were used. A post-embedding procedure carried out on tissue sections embedded in LR-White was applied to differentiate between the sensory cells: The lectins from Helix pomatia (HPA) and Triticum vulgare (WGA) bound to N- acetyl-galactosamine and to N-acetylglucosamine residues occurring especially in vesicles of dark sensory cells. This indicates a secretory function of these cells. Most light sensory cells — with some exceptions, probably immature cells —, are HPA-negative. The mucus of the receptor field and at the top of the adjacent epithelial cells was strongly HPA-positive. Pre-embedding studies were performed in order to obtain information about the reaction of the mucus with lectins under supravital conditions. The mucus of the taste bud receptor field exhibited intensive binding to WGA, but not to the other lectins tested. Most lectins bound predominantly to the surface mucus of the nonsensory epithelium and to the marginal cells close to the receptor field. The strong lectin binding to mucins and the relatively weak lectin binding to cell surface membranes in pre-embedding studies suggest that the mucus possibly serves as a barrier which is passed selectively only by a small amount of lectins or lectincarbohydrate complexes. Lectin-carbohydrate interactions may play a role in recognition phenomena on the plasmalemmata of the taste bud sensory cells. Recognition processes directed to bacteria or viruses should be considered as well.Parts of this investigation were presented at the XI. Annual Meeting of the Association for Chemoreception Sciences (AChemS XI), held at Sarasota, Fl, April 12–14, 1989 (Witt and Reutter 1989)     

Membrane integrity, mitochondrial activity, ATP content, and motility of the European catfish (Silurus glanis) testicular spermatozoa after freezing with different cryoprotectants.

The extent of cellular damage was investigated after freeze-thawing of the European catfish testicular sperm with various cryoprotectants. The best protection was given by dimethylacetamide (10 and 15%) in a sucrose solution. Under these conditions, the percentage of cells with an intact membrane was high (90%), and the protection of the activity of the mitochondria was medium (47%). It was shown that the addition of dimethylacetamide largely increased the ATP content of the spermatozoa. It is suggested that this phenomenon is a decisive factor for the freezing resistance of European catfish testicular spermatozoa in the presence of dimethylacetamide (60% motility after thawing versus 90% before freezing).     

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.     

Susceptibility of European catfish (Silurus gianis) to Edwardsiella ictaluri

European catfish (Silurus glanis) were tested for their susceptibility to the bacterium Edwardsiella ictaluri. The LD₅₀ of E. ictaluri when injected into European catfish was 5.4 × 10⁶ compared to 7.1 times; 10⁴ for channel catfish (Ictalurus punctatus). E. ictaluri was isolated from dead and moribund European catfish and the bacterium was also detected in kidney smears by an indirect fluorescent antibody (FA) technique. The bacterium was not isolated or detected by FA from surviving fish 15 days after injection. No clinical signs of E. ictaluri infection were noted in European catfish, but these were prevalent in the channel catfish. These experiments indicate that under experimental conditions European catfish are not as susceptible to E. ictaluri as channel catfish.     

Production,consumption and prey availability of northern pike (Esox lucius), pikeperch (Stizostedion lucioperca) and European catfish (Silurus glanis): a bioenergetics approach

Bioenergetics models were applied for the assessment of food consumption of northern pike, pikeperch and European catfish in drainable ponds of 0.4 ha. The ponds were stocked with known numbers of the 0⁺ predators. The prey fish consisted of naturally recruited 0⁺ cyprinids (rudd, roach and bream). The study shows that the impact of the three 0⁺ piscivores on the aquatic system differs, which is related to the feeding behaviour and habitat use of the fish. All piscivores realised part of their production on a non-fish diet.     

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.     

Spawning and season affect lipid content and fatty acid composition of ovary and liver in Japanese catfish (Silurus asotus)

The influences of spawning and season on lipid content, lipid classes, and fatty acid composition were assessed in ovary and liver of wild and cultured Japanese catfish (Silurus asotus). The lipid content (7.3+/-1.6 g/100 g wet wt.) of ovary from wild catfish at spawning was higher than that at post-spawn. However, no influence of spawning on the lipid content of liver was observed. Docosahexaenoic acid [DHA, C22:6(n-3)] in ovary lipids was 12.3+/-0.5% of total fatty acids. The percentage of n-7 monounsaturated fatty acids in triacylglycerol from the ovary and liver in the spawning season was high. Percentages of C22:6(n-3) in phosphatidylcholine and phosphatidylethanolamine from ovary were higher during spawning than after spawning. No significant differences were observed in the lipid content of ovary and liver from cultured catfish between seasons (summer vs. winter). Content of arachidonic acid (C20:4n-6) in ovary and liver from cultured catfish was higher in summer than in winter. There were differences in lipid classes of ovary and liver by spawning and season. These results suggest that the lipid metabolism in Japanese catfish is greatly influenced by spawning and season.     

南方鲇

南方鲇是我国特有的大型肉食性名优鱼类。具有个体大,生长快,抗病力强等特点。其形态特征、生活习性、繁殖与生长、人工养殖等都具有自身的特殊性,也是一种很好的实验研究材料。     

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.     

Influence of protein content of diet on growth and lipid composition of European eel muscle and liver

The influence of diet protein content (35-45-55%) on growth and lipid composition of muscle and liver of European eel (Anguilla anguilla) was studied for the first time. In control eel, triacylglycerols constituted about 90% of total lipids in muscle and about 40% in liver. Triacylglycerol content in eel muscle significantly increased after two months of treatment with any diet assayed, with independence of protein content and source. In liver, this increase was comparatively higher in herring meal diets. Total phospholipid content in both muscle and liver drastically decreased after one month of all the experimental treatments, although some recuperation was found at the second month. No significant differences in lipid composition of muscle eel were found among the various experimental groups, in spite of the differences observed in the body weight gain.