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Animals use dispersed resources within their home range (HR) during regular day-to-day activities. The high-quality area intensively used by an individual, where critical resources are concentrated, has been designated as the core area (CA). This study aimed to describe how animals utilize energy in the HR and CA assuming that changes would occur according to the size of the used areas. We observed energetic costs of space use in the largest European freshwater predator catfish, Silurus glanis, using physiological sensors. Catfish consumed significantly more energy within the CA compared to the rest of the HR area. In addition, energetic costs of space use within a large area were lower. These results generally indicate that utilization of larger areas is related to less demanding activities, such as patrolling and searching for new resources and mates. In contrast, fish occurrence in small areas appears to be related to energetically demanding use of spatially limited resources.

Some features of the biology of European catfish Silurus glanis in the Lower Kama Reservoir (Nizhnekamsk Reservoir) are elucidated for the first time based on the materials collected in 2005–2017. The size–age structure, sex composition, and growth rate of catfish are analyzed. A trend towards an increase in catfish catches is noted, which is also currently observed in other reservoirs.

Seasonal distribution, biology of reproduction, body length/weight composition, age of sexual maturation, and features of feeding in wels catfish Silurus glanis from the Volga River channel areas within the Volga–Ahtuba water systems (the lower Volga) have been studied. Within the study region, wels habitats are confined to the system of river-channel pits and to the deep-water sites of the main river channel; the fish roam within the surroundings of the pits. Wels spawns in the waterbodies of the subordinate system of the river: eriks (shallow channels) and branches between the Volga and Ahtuba rivers. In the study region, wels is represented by a long-lived late-maturing group. The fish of different body lengths/weights differ in the feeding modes: the specimens with body weights of <5 kg consume various small-sized prey, including nonfish food; larger individuals feed on large fish prey. Comparative analysis of the structures of wels populations from the Volga River delta and channel areas revealed considerable differences indicating the presence of two spatial groups of the population or subpopulation ranks: deltaic migrant and river channel settled. Development of an optimal strategy for exploitation of this valuable fish necessitates a differentiated approach and detailed analysis of biological traits of this species within the Volga basin. Such analysis should include population-genetic methods.

The study of epizoic diatoms in freshwater habitats is a practically virtually unexplored field of research that offers interesting perspectives from different points of view. In the present study, we have considered the invasive allochthonous fish Silurus glanis as a basibiont of epizoic diatoms. Recently, this species has undergone an impressive expansion in the main Italian hydrographic networks, leading to an increasing number of projects aimed at its control and/or eradication. The main objectives of our study were to shed light on the diatom species able to colonise the skin of S. glanis, highlighting possible putative obligate epizoic taxa and the possible role of S. glanis as a vector for allochthonous or potentially invasive diatoms. Epizoic diatom samples on S. glanis were surprisingly rich and diverse, confirming that the skin of this fish is a suitable substrate for the growth of these algae. We did not observe any obligate epibiont. Silurus glanis hosted very site-specific communities, confirming its strong site fidelity and sedentary habits. Interestingly, smaller individuals did not host a well-developed epizoic diatom community, probably due to behavioural and physiological issues, here discussed. Finally, our results highlighted that S. glanis is likely to be a suitable vector for allochthonous and/or invasive diatom taxa, such as Achnanthidium delmontii. In conclusion, the analysis of epizoic diatom communities can provide useful information on host habits, which is particularly important in the framework of management and eradication programmes, and can indirectly serve to control the spread of allochthonous and/or invasive diatoms.

Artificial reproduction of European catfish Silurus glanis was embarrassed by problems with stripping high-quality milt without contamination by urine. Analogical difficulties were noticed during milt stripping in male African catfish Clarias gariepinus. So fish-farmers sacrificed male catfishes for artificial propagation. Alternative method is non-lethal laparotomy for sperm collection. In this work we used surgical techniques for partial resection of testicular tissue in male catfish in vivo and a new method of urine descent before sperm selection. General anaesthesia was performed by immersion of fishes in tank with 25 L water with clove oil at the dose of 0.04 mL L-1. Only a small incision (5-8 cm) was sufficient for ablation of part of testis. For the first time, separate sutures were applied to the peritoneum and skin for creating additional anastomoses which hold and fix internal organs. The regeneration of testis was noted. As alternative to surgical method we used catheterization of urine bladder before sperm collection. These methods are designed to keep alive male catfishes and to obtain high-quality milt without contamination by urine. The techniques of partial gonadectomy and urinary bladder catheterization could be used in farming and conservation aquaculture of European catfish and other silurids.

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.

Apex predators play a key role in ecosystem stability across environments but their numbers in general are decreasing. By contrast, European catfish ( Silurus glanis ), the European freshwater apex predator, is on the increase. However, studies concerning apex predators in freshwaters are scarce in comparison to those in terrestrial and marine ecosystems. The present study combines stomach content and stable isotope analyses with diet preferences of catfish to reveal its impact on the ecosystem since stocking. Catfish niche width is extremely wide in comparison to the typical model predator, Northern pike ( Esox lucius ). Catfish and pike have different individual dietary specialization that results in different functional roles in coupling or compartmentalizing distinct food webs. The role of both species in the ecosystem is irreplaceable due to multiple predator effects. The impact of catfish is apparent across the entire aquatic ecosystem, but herbivores are the most affected ecological group. The key feature of catfish, and probably a common feature of apex predators in general, is utilization of several dietary strategies by individuals within a population: long-term generalism or specialization and also short-term specialization. Catfish, similar to other large-bodied apex predators, have two typical features: enormous generalism and adaptability to new prey sources.

Sea lamprey ( Petromyzon marinus ) is a unique jawless vertebrate among the most primitive of all living vertebrates. This migratory fish is endangered in much of its native area due to dams, overfishing, pollution, and habitat loss. An introduced predator, the European catfish ( Silurus glanis ), is now widespread in Western and Southern European freshwaters, adding a new threat for sea lamprey migrating into freshwater to spawn. Here, we use a new prototype predation tag coupled with RFID telemetry on 49 individuals from one of the largest sea lamprey European populations (Southwestern France) to quantify the risk of predation for adult sea lampreys during its spawning migration in rivers with large populations of European catfish. We found that at least 80% of tagged sea lampreys (39 among 49) were preyed upon within one month, and that 50% of the released lampreys were rapidly consumed on average 8 days after tagging. This very high predation rate suggests that the European catfish represents a supplementary serious threat of extirpation for the native sea lamprey population we studied. This threat is likely to happen throughout most of the native lamprey distribution area, as the European catfish is becoming established almost everywhere the sea lamprey is.

The number of artisanal fishers and consequently their catch in the Sava River have been declining significantly for years. The aim of this study is therefore to examine how this affects the average weight of the most important fish species caught. The average weight increased significantly for bream Abramis brama (P < 0.01), pike-perch Sander lucioperca (P < 0.01) and wels catfish Silurus glanis (P < 0.05), while this was not the case for common carp Cyprinus carpio and pike Esox lucius (P > 0.05). Although recreational anglers also catch fish in the same waters, together with the two groups of fishermen from Bosnia and Herzegovina from the other bank of the river, it is expected that the average weight of the main fish caught will not decrease under the current circumstances.

The extreme body sizes of megafishes associated with their high commercial values and recreational interests have made them highly threatened in their native range worldwide by human-induced impacts such as overexploitation. Meanwhile, some megafishes have been introduced outside of their native range. A notable example is the European catfish (Silurus glanis), one of the few siluriforms native to Eastern Europe. It is among the 20 largest freshwater fish worldwide, attaining a total length over 2.7 m and a documented mass of 130 kg. Its distinct phylogeny and extreme size imply many features that are rare among other European fish, including novel behaviours (massive aggregations, beaching), consumption of large bodied prey, fast growth rates, long lifespan, high fecundity, nest guarding and large egg sizes. The spread of the species is likely to continue due to illegal introductions, primarily for recreational angling, coupled with natural range extension associated with climate change. Here, the most recent knowledge on the current distribution and the ecology of the species are reviewed. A series of key research questions are identified that should stimulate new research on this intriguing, yet largely unknown, species and, more generally, on the ecology of freshwater invaders.