Systemic amoebiasis in cultured European catfish, Silurus glanis L.

Abstract. Parasitic cells resembling amoeba trophozoites were found histologically and ultrastructurally to be associated with severe proliferate gill disease and systemic infection often leading to extensive granulomatous tissue changes in the European catfish, Silurus glanis L. Infections with the normally free-living amoeba leading to mortalities of up to 30% were considered to result from suboptimal water quality with heavy bacterial loading in a heated partial recirculation system.     

Triploidization of European catfish, Silurus glanis L., by heat shock

Heat shock was applied to fertilized eggs of European catfish, Silurus glanis L., for the induction of triploidy. A heat shock of 40. 5°C lasting 1 min and starting 9 min after gamete activation gave the best results with 88.93% of hatched viable fry (92.41% in control group). Yields of hatched viable triploid fry reached 63.14% or 50.60%, when expressed as percentage of the absolute number of viable fry or number of living eggs in eye-bud stage, respectively (P < 0.05).     

Different growth and processing traits in males and females of European catfish,Silurus glanis

Two experiments were developed in France to assess whether growth and processing traits differ for males and females in the European catfish, Silurus glanis. In the first experiment, fish were raised from 5 to 200 g in a pond for 7 months. A significant sex effect is demonstrated in males for live weight at the end of the experiment (males 147.5±5.4 g vs females 132.9±4.9 g) and head index (males 20.6±0.1 % vs females 21.2±0.1 %, P < 0.05). In the second experiment, fish were raised from 885±196 g to 2 266±418 g in a recirculated system at 20.7±1.4 °C for 120 days. A differential growth between the sexes is also registered. Males are heavier and longer (+ 357 g or + 17.0 % and + 6.2 % in length at day 120) and present a higher gutted weight and yield (+ 367 g or + 18.7 %; 95.0±0.9 % vs 93.8±1.8 %) and fillet weight (+ 233 g or + 20.9 %) than females after slaughter.     

Steroidogenesis by ovaries and testes of the European catfish,the wels (Silurus glanis), in vitro

Testosterone, 3,17-dihydroxy-5-pregnen-20-one, 17,20-dihydroxy-4-pregnen-3-one (17,20P) and 5-pregnane-3,17,20-triol were identified as the major metabolites of [³H] 17-hydroxyprogesterone in ovarian incubations of the European catfish Silurus glanis. 17,20P and the reduced triol were present only in ovaries from fish primed with carp hypophysial homogenate (chh) while testosterone yields were significantly higher in controls than in treated fish. 11-Ketotestosterone, 11-hydroxytestosterone and 17,20-dihydroxy-4-pregnen-3-one (17,20P) were identified as the major metabolites of [³H]17-hydroxyprogesterone in in vitro incubations of testes of a spermiating catfish. There was no significant production of conjugates or other water soluble metabolites by either sex. The stimulation of plasma 17,20P, 17,20P and 11-hydroxytestosterone by chh in primed but not control males suggests that the role of these steroids in spermiation should be further examined.     

Haematological and biochemical alterations in Korean catfish, Silurus asotus, experimentally infected with Edwardsiella tarda

This study determined the haematological changes in Korean catfish, Silurus asotus , experimentally infected with Edwardsiella tarda . Twenty-four or 48 h after infection with 1 × 10⁴ colony-forming units (CFU) mL⁻¹ of E. tarda , the fish were anaesthetized and the blood was collected. The haematological and biochemical tests included haematocrit (Ht), haemoglobin (Hb), leucocyte counts (Lc), total calcium (Ca), total protein (TP) concentration, alkaline phosphatase (ALP), glucose (GLU), aspartate aminotransferase, lysozyme and differential leucocyte populations. After 24- and 48-h infection, the values of Ht, Hb, Lc, TP, ALP and GLU were significantly decreased with respect to the control. Aspartate aminotransferase and lysozyme activity in both the 24- and 48-h groups exhibited higher levels compared with those in the control. However, the bacterial infection did not induce any significant alteration in the Ca concentration. After the 48-h infection, neutrophils and macrophage populations were reduced whereas lymphocytes were increased with respect to those in the control and the 24-h infection groups. The present study demonstrates that E. tarda infection causes haemato-biochemical responses that are related to the general physiological condition and defence system in catfish.     

Artificial spawning of European catfish Silurus glanis L.: differences between propagation results after stimulation of ovulation with carp pituitary and Ovopel

The effect of spawning on European catfish females with an average body weight of 5.6 kg and 11.2 kg was investigated, with carp pituitary and Ovopel being used as ovulation stimulators. Ovopel induced ovulation in a higher percentage of females of both smaller and larger body weight. The applied ovulation stimulators did not significantly affect the weight of the obtained eggs. On the other hand, the effect of the stimulators was highly significant (P≤ 0.01) with respect to the percentage of live embryos after 24‐, 48‐ and 56‐h incubation. The fish of greater body weight yielded eggs of a significantly (P≤ 0.05) greater weight, although of poorer quality. The interaction between the ovulation stimulator and female body weight was statistically significant (P≤ 0.05) for the weight of the obtained eggs and highly significant (P≤ 0.01) for the percentage of live embryos after 48‐h incubation. For the percentage of live embryos after 24‐ and 56‐h incubation, the statistical significance (P≤ 0.05) of this interaction was determined. In the case of females of smaller body weight, a statistically significant (P≤ 0.05) phenotypic correlation was found between the percentage of live embryos after 24‐h incubation and that after 48‐h incubation, and also between the percentage of live embryos after 24‐ and 56‐h incubation.     

Growth performance, feed intake and morphology of juvenile European catfish, Silurus glanis (L.) fed diets containing different protein and lipid levels

The study was carried out with juvenile European catfish to evaluate the effects of commercial diets on growth, feed utilization and changes of selected morphometric traits of fish. Three diets containing different levels of crude protein and lipid: 37 and 12 %, 45 and 15 %, 45 and 20 %, respectively, were fed to triplicate groups of European catfish for 50 days. The fish were fed continuously (24 h day^?1) by automatic belt feeders for fish with a clock drive. Biometric characteristics of fish included the determination of plasticity traits using modified Pravdin method. Fish growth rate and final body weight were statistically higher in variant 45/20 diet (specific growth rate of 2.6 % day^?1). The intergroup significant differences were recorded for food conversion ratio (FCR) and protein efficiency ratio (PER), during the particular decades of the experiment. For the whole period of the growth test, no significant differences in FCR were observed, but the most favorable values of PER were obtained in variant 37/12. Protein retention in fish body ranged from 18.7 to 21.0 %, and fat retention was significantly more variable, ranged from 87.5 to 121.3 %. Fish survival rate recorded during the growth test was higher in all variants (above 95 %). Statistically significant increases in protein and lipid content were found in fish fed diets 45/15 and 45/20. The tested diets have no effect on changes in fish body proportions. The most effective in juvenile European catfish rearing was diet with 45 % of crude protein and 20 % of lipid.     

Evaluation of body weight and color of cultured European catfish (Silurus glanis) and African catfish (Clarias gariepinus) using image analysis

Two cultured catfish species (European catfish Silurus glanis, and African catfish Clarias gariepinus) were evaluated for their weight estimation and colors by image analysis. A total of 60 whole fish from each species were first weighed, and then their pictures taken by a digital camera in a light box. Length, weight and color of all fish were determined by image analysis and results were compared between the two fish. Fish weight ranged from 7.4 to 39.61 g and 25.71 to 93.91 g for European and African catfish, respectively. Weight (W) vs length (L) data were fitted linear (W = A + BL), power (W = A L^B) and second order polynomial equations (W = C₀ + C₁ L + C₂ L²). The R² values ranged from 0.835 to 0.974. For the W vs view area (V) relationship, the same equations were used. The R² values for these equations ranged from 0.927 to 0.972. No significant difference was found between the average color values according to the L*, a* and b* distributions for both fish species (P > .05). Image analysis can easily determine length, view area, and color of fish and help in developing W vs L, and W vs V relationships.     

Effect of a constant magnetic field on water quality and rearing of European sheatfish Silurus glanis L. larvae

The influence of a constant magnetic field with an intensity ranging from 0.4 to 0.6 T (Tesla) was determined on physicochemical parameters of water and on rearing of larvae of the European sheatfish Silurus glanis L. larvae. In the experiment, feeding brood of European sheatfish was reared in two groups. One was kept in tanks supplied with magnetically treated water. The second group was kept in tanks supplied with water without treatment with a magnetic field (control). The fish tanks were supplied with circulating river water. Rearing was conducted for 15 days at an initial stocking density for both groups of 8 fish per litre. The mean fish mass obtained was 0.46 g, and in the control group – 0.78 g (P<0.05). Stocking mortality was 19.1% in the tanks with a constant magnetic field, and 13.5% in the control group. No changes were observed in water phosphate, ammonium, organic compounds or chloride concentrations.     

Replacement of fish meal with rapeseed protein concentrate in diets fed to wels catfish (Silurus glanis L.)

The potential of rapeseed protein concentrate as fish meal alternative in diets for wels catfish (initial average weight 86.5 ± 1.9 g) was evaluated. Sixteen fish were stocked into each of 12 experimental tanks being part of a freshwater recirculation system. Fish were organized in triplicate groups and received isonitrogenous (603 ± 3 g CP kg^?1) and isocaloric (23.0 ± 0.3 kJ g^?1) experimental diets with 0%, 25%, 50% and 75% of fish meal replaced with rapeseed protein concentrate (710 g CP kg^?1). At the end of the 63‐day feeding period, weight gain, standard growth rate, feed intake, feed conversion ratio and protein efficiency showed no significant difference between control group and fish fed on diets with 25% reduced fish meal content by inclusion of rapeseed protein concentrate. Higher dietary fish meal replacement negatively affected diet quality and palatability resulting in reduced feed intake, feed efficiencies and fish performance. However, blood serum values of triglycerides, glucose and protein were not significantly different between treatment groups, still indicating a favourable nutrient supply from all experimental diets.     

Investigating the catch returns and growth rate of wels catfish, Silurus glanis, using mark–recapture

Abstract In January 2004, 46 wels catfish, Silurus glanis L., between 51 and 135 cm total length were tagged and released into a 0.4 ha recreational, catch and release, lake fishery in the UK, and their recapture by anglers monitored throughout the year. Of the 46 tagged fish, 16 were recaptured by anglers during 170 capture events. Some individual fish were captured up to 26 times. Catfish <75 cm appeared to be the least susceptible to capture and fish >100 cm most susceptible. Frequency of captures increased with temperatures >10 °C and peaked between June and August. Selected recapture weight data were used to produce a mass specific growth equation and revealed specific growth rate was a decreasing function of body mass over the size range of the recaptured fish. Their growth was slower than fish from elsewhere in their distribution range.     

Brief communication: rapid elimination of egg stickiness using sodium hypochlorite in wels catfish Silurus glanis

Fish Physiology and Biochemistry - The wels catfish Silurus glanis is valuable fish for aquaculture. Its production relies mainly on artificial reproduction. One of the crucial steps determining...     

Preliminary telemetry data on the movement patterns and habitat use of European catfish (Silurus glanis) in a reservoir of the River Ebro, Spain

Abstract –  Knowledge of the movements and diel behaviour of the European catfish ( Silurus glanis ), the largest European freshwater fish, is limited to anecdotal information. In a preliminary telemetry study of European catfish, the spring diel movement patterns of five adult catfish were examined. After intraperitoneal insertion of the acoustic tags, the positions of the fish were recorded automatically in the Flix Reservoir (River Ebro, NE Spain). A marked nocturnal mobility pattern was observed throughout the study. During daytime, the catfish were consistently located in the littoral zone and spent extended periods of the day hidden in concealed habitats. Catfish movements were in a radial pattern, with upstream and downstream excursions followed by returns to a previously occupied location. Significant individual variations in movement pattern were observed among the tagged fish and within the 24 h cycle for each fish. Mean instantaneous swimming speed was 0.17 body lengths per second (BL·s⁻¹) at night but 0.09 BL·s⁻¹ during the daytime.     

Detection of channel catfish virus DNA in acutely infected channel catfish, Ictalurus punctatus (Rafinesque), using the polymerase chain reaction

Channel catfish virus (CCV) causes an acute haemorrhagic disease in channel catfish, Ictalurus punctatus (Rafinesque), fry and fingerlings. The present study describes a polymerase chain reaction (PCR)-based assay for detection of CCV DNA in the tissues of acutely infected juvenile catfish. The assay is rapid, sensitive and specifically detects CCV DNA derived from epidemiologically distinct viral isolates. The use of two independent PCR primers sets, each specific for particular CCV genes (open reading frames 8 and 59), provides a means to confirm the results and minimize false-positive results. The method identifies CCV DNA in several tissues of acutely infected fish, including the brain, blood, intestine, kidney and liver. The CCV PCR assay is useful for the diagnosis of acute CCV disease and for studies to investigate the molecular basis of CCV pathogenesis.     

Histopathology of experimental Streptococcus sp. infection in tilapia, Oroochromis niloticus (L.), and channel catfish, Ictafurus punctatus (Ratinesque)

Nile tilapia, Oreochromis niloticus (L.), and channel catfish, Ictalurus punctatus (Rafinesque), were experimentally infected by immersion with three isolates (Lake, DL8O5 and MS91452) of Streptococcus sp. from diseased fish. To enhance infection, the lateral body surface of each fish was scraped prior to bacterial exposure. The Lake and DL8O5 isolates caused exophthalmia, ocular opacity and ocular haemorrhage in some tilapia. Histopathology of these fish revealed; meningitis; polyserositis of heart, liver, spleen, ovary and kidney; splenitis; ovaritis; and myocarditis. Isolate MS91452 induced only mild granulomas in spleen, kidney and ovary of tilapia. The Lake and DL8O5 isolates induced endophthalitis, Channel catfish infected with the Lake and DL805 isolates developed similar eye lesions to tilapia. Histologic lesions caused by all three isolates in channel catfish consisted of meningoencephalitis, mild myocarditis, splenitis and ovaritis, but these lesions were not as severe as in Nile tilapia.