European Catfish Silurus Glanis Research Articles

Ecosystem based approach to assess the impact of invasive or expanding species in the lower Saône River

The spread of invasive alien species is identified as one of the most important threats to freshwater ecosystems as they can modify their trophic structure, biomass and flows. The lower Saône River is one of the most biologically productive waterways in France. It has been in strong interaction with a wide range of human activities such as fisheries for at least three millennia. To implement an ecosystem based approach, an Ecopath static trophic model was used for the first time in this river to quantify the role of three invasive or expanding species over two contrasted periods (1988–1993 and 1994–2005). The parameters used in the model integrate on the one hand catch data from fishers (professional, amateur fishing gear users, and anglers), and on the other hand the available literature data on species biomass, diet and the expert assessments of scientists and managers. Species such as the filtering Asian clam Corbicula fluminea may explain the triggering of the ecosystem shift towards a functioning where summer phytoplankton blooms are rarer. In the high trophic levels, the great cormorant Phalacrocorax carbo appears to have low trophic impact while the development of a large population of European catfish Silurus glanis has a strong effect, maintaining important trophic flows in the ecosystem in substitution for the decrease in angling landings.

The effect of parasitism on boldness and sheltering behaviour in albino and pigmented European catfish (Silurus glanis)

Parasites can change the behaviour of their hosts, but little attention has been given to the relationship between parasite effects on host behaviour and colouration. The correlation between disrupted melanin production and alterations in various physiological and behavioural traits, e.g., aggression, shoaling behaviour, stress responsiveness and sensitivity to brood parasitism, has been reported in albino fish. We hypothesized that parasitism would affect the behaviour of albino and pigmented conspecifics differently. In laboratory conditions, we infested a group of pigmented and a group of albino individuals of European catfish Silurus glanis with glochidia of two Uninoidea species, namely, the native species Anodonta anatina and the invasive species Sinanodonta woodiana, and investigated the effect of parasitization on the boldness and sheltering behaviour of the hosts. The behaviour of albino individuals differed from that of pigmented conspecifics both before and after parasitization. Parasitization with glochidia did not affect sheltering behaviour, but it increased boldness in pigmented individuals, whereas albino individuals did not exhibit any changes in behaviour. Sheltering results were consistent in both binomial and continuous variable analyses, whereas boldness was significant only in the binomial analyses. Our results demonstrate the reduced susceptibility of the albino phenotype to glochidia infestation, together with questions of the choice of analyses.

Molecular and SEM studies on Thaparocleidus vistulensis (Siwak, 1932) (Monopisthocotyla, Ancylodiscoididae)

Presenting new molecular and scanning electron microscope (SEM) features, this study gives additional data to the better knowledge of Thaparocleidus vistulensis (Siwak, 1932) (Monopisthocotyla, Ancylodiscoididae), a parasite of the European catfish Silurus glanis Linnaeus, 1758 (Siluriformes, Siluridae) cultured in a commercial fish farm in Hungary. In addition, notes on the early development of sclerotized anchors are also provided. The main morphological difference of T. vistulensis compared to other congeneric species is associated with the male copulatory organ, which exhibits 5–7 loops in the middle of the penis length and a long open V-shaped sclerotized accessory piece, dividing terminally into two parts, securing the terminal part of the penis tube. The present study provides for the first time molecular characterization data based on the 2694 bp long nucleotide sequence of rDNA (ITS1, 5.8S, ITS2, and flanked with partial 18S and partial 28S) submitted in GenBank with the accession number OR916383. A phylogenetic tree based on ITS1 sequences supports a well-defined clade including T. vistulensis, forming a sister group with T. siluri, a species-specific monopisthocotylan parasite to S. glanis. The morphological characterization of T. vistulensis, especially for the male copulatory organ, together with the molecular data in the present study, extends knowledge about this monopisthocotylan species and provides new information for future phylogeny studies.

Correction: European catfish Silurus glanis behaviour in response to a strong summer hypoxic event in a shallow lake

Correction: European catfish Silurus glanis behaviour in response to a strong summer hypoxic event in a shallow lake

Predicting the potential implications of perch (Perca fluviatilis) introductions to a biodiversity-rich lake using stable isotope analysis

Biological invasions, particularly of fish species, significantly threaten aquatic ecosystems. Among these invaders, the introduction of the European perch (Perca fluviatilis) can have particularly detrimental effects on native communities, affecting both ecosystem functioning and human well-being. In this study, carbon and nitrogen stable isotope analysis was employed, using perch originating from five different ecosystems, to model the effects of their hypothetical introduction into İznik Lake, an economically and ecologically important, biodiversity-rich lake in northern Turkey, to ultimately assess their potential predation impact and competition with native predators. The results revealed that if perch were introduced to the community, they would – considering gape size limitations – primarily prey upon Vimba vimba and Rutilus rutilus, indicating a significant feeding pressure on these species. Furthermore, the study identified a potential overlap and competition for resources between commonly mesopredator perch and the European catfish Silurus glanis, the current top predator in the ecosystem. Both species would occupy top predatory positions, emphasizing the potential disruption of predator–prey dynamics. Our findings underscore the potential ecological repercussions of perch invasions. The selective predation on V. vimba and R. rutilus, with the latter being consumed to a lesser extent by perch, could lead to cascading effects throughout the food web, altering the community structure, and ecosystem dynamics. Additionally, the competition between perch and S. glanis raises concerns about effects on the stability and functioning of the fish community. These results highlight the need for proactive management strategies to mitigate the risk of perch introductions. Strict regulations on the movement and introduction of invasive species, along with comprehensive monitoring, are crucial for preserving native communities and maintaining the ecological integrity of freshwater ecosystems. Our study demonstrates the potential predation impact of perch on vulnerable fish species and the competition with the established apex predator, emphasizing the importance of considering the ecological consequences of perch invasions and informing management decisions to ensure the conservation and sustainability of aquatic ecosystems.

Patterns of genetic variation in native and non-native populations of European catfish Silurus glanis across Europe

Patterns of genetic variation in native and non-native populations of European catfish Silurus glanis across Europe

Westwards expansion of the European catfish Silurus glanis in the Douro River (Portugal)

The current study reports the first occurrence and the spread of the European catfish Silurus glanis (Family: Siluridae) in the Portuguese section of the Douro River, suggesting a potential expansion of its distribution in Portugal either via westward dispersal across international rivers and/or human-assisted introductions into new reservoirs and drainages. The European catfish has unique features (e.g., opportunistic predator, hunting, and aggregation behaviour) that make it highly suitable for establishing self-sustaining populations in new areas and likely contribute to its invasion success. The species may severely affect native prey communities and modify food web structure and ecosystem functioning. Efficient and sustainable management actions are needed to prevent further introductions in the future.

Interannual variability in the trophic niche of young‐of‐year fish belonging to four piscivorous species coexisting in a natural lake

Abstract Predatory fish species play a key role in aquatic ecosystems by exerting top‐down control on the food web. Also, their intra‐guild trophic interactions (i.e. competition) are crucial for the stability of the community. However, most studies focus on adult stages, while juveniles remain poorly studied, although their recruitment is the basis for the maintenance of predator populations. We analysed carbon and nitrogen stable isotopes ratios of the young‐of‐year of four coexisting widespread predatory fish species (northern pike Esox lucius, European perch Perca fluviatilis, pikeperch Sander lucioperca, and European catfish Silurus glanis), sampled over 3 years in a shallow natural lake. We found that the hierarchy in trophic position between species was consistent across years and similar to that known for adults, but with large variations around a general pattern: pike and pikeperch tended to occupy the highest trophic positions while perch occupied the lowest, and catfish had very varying positions. Species partitioned their niches to decrease interspecific competition, but with some occasional overlaps, contributing to preserving their body condition. Depending on density, which was particularly impacted by harsh environmental conditions, niche overlap fluctuated across years, leading to niche enlargement of densely populated species, except for catfish. These mechanisms enabled species coexistence, allowing the co‐occurrence of alien and native predators within the same ecosystem. This work advocates for time‐integrated studies of trophic webs because they capture the variability of their dynamics better than a static picture. This is particularly true for juveniles whose survival strongly depends on their capacity to cope with competition. Information from trophic mid‐term studies of juveniles provides valuable guidance for optimised management of species.

Fishes in the economy of Ancient Greek colonies (600 BC – 300 AD) on the Northern Black Sea Coast – new touches to an old portrait

The article presents the results of a thorough study of fish remains recovered during the excavations of three ancient Greek cities (Olbia, Berezan and Chornomorka) in the northern part of the Black Sea coast. These materials are dated in the range of 600 BC – 300 AC (in the case of Olbia and Berezan), and 500–400 BC for Chornomorka. Fish bones were processed for the identification of species used by the inhabitants of these ancient cities for food. The remains of about ten fish species are present in the studied sample. Of them, sturgeons (Acipenser spp.) were the most numerous in the region at that time. The other species which were usually caught in these ancient Greek cities are mostly represented by carp fishes (roach, common bream, white bream, blue bream, common carp, and crucian carp), but also European catfish Silurus glanis, pike Esox lucius, and pikeperch Sander lucioperca. The weight and size of some fish individuals were reconstructed based on complete bones. Comparison of the specimens from individual samples (series) showed no significant differences in their total length and weight. The economic activity of ancient settlements of the Northern Black Sea region is of interest to archaeologists for a long time. Many of the aspects of this activity, such as agriculture, crafts, and architecture, have been explored quite well (e.g., Christodoulou 2016 and references therein). At the same time, fishery, an important direction of the economy of coastal cities providing a valuable animal protein, often falls out of the scope of research interests. A significant amount of materials collected by archaeologists in the north of the Black Sea coast during the 20th century is still not processed and remains unpublished. Therefore, it is difficult to create a holistic picture of the economy of ancient Greek cities. A valuable information about fishing and fish consumption in ancient cities of the Northern Black Sea region according to archaeological data and osteological collections is presented in Lebedev (1960), Zhiteneva (1964), Hojte (2005), Morales et al. (2007) and Odrin (2010). A few recent publications are focused on the fish osteological material from ancient Greek cities discovered on the Northern Black Sea coast. Archaeozoological studies can show how important fish was in the diet of people, which species were preferred, and how intensive was fishing in this region in different periods. In addition, it is possible to find out whether there was a fish trade between these cities using the ratio of cranial and postcranial elements of the skeleton. Such studies can prove or disprove the statements of Strabo or Herodotus, who wrote about the culinary preferences of ancient Greeks. Therefore, the aim of this article is to present in detail the results of the study of fish bone samples from Olbia, Berezan and Chornomorka in the range from their formation (600 BC) until the end of the Roman period (300 AD). By comparing data from different periods, it is possible to track the role of fishery in the economy of these settlements and its dynamics over time. Key words: Olbia, antiquity, Berezan, archaeozoology, fishing, ancient Greeks, Black Sea

European catfish Silurus glanis behaviour in response to a strong summer hypoxic event in a shallow lake

Hypoxic events have always naturally occurred in freshwater ecosystems but are worsening due to anthropogenic activities. Hypoxia tolerance greatly varies among fish species and is difficult to quantify in nature in large fish species. We analysed the movements of 40 subadult and adult European catfish Silurus glanis [(727; 2150) mm] exposed to a natural summer hypoxic event in a shallow lake of southeastern France. Catfish could withstand very low dissolved oxygen concentrations (DOC), down to 1.3 mg/L in the upper half of the water column (corresponding to a mean dissolved oxygen saturation rate of 16%), when their preferred benthic habitats were anoxic. While hypoxia was becoming more severe, individuals significantly increased their activity and the surface area they visited, whatever their size. This led them to a refuge zone where they aggregated or stayed in close vicinity, very little mobile, over one and a half day during the overall anoxia of the lake. This zone, located very close to the well oxygenated water inflow, was probably one of the most oxygenated accessible zone. However, during this aggregation, the smallest individuals were more active than the largest ones. This was probably because they more often needed to move to better-oxygenated places within the gathering area, compared to larger dominant fish that occupied the best places. The ability of catfish to withstand very low DOC, along with its high optimum temperature range, could give it a competitive advantage over other predatory species in the context of global change.

Comparative study of stress responses, laterality and familiarity recognition between albino and pigmented fish

Oculocutaneous albinism is the result of a combination of homozygous recessive mutations that block the synthesis of the tyrosine and melatonin hormones. This disability is associated with physiological limitations, e.g., visual impairment expressed by lower visual acuity and movement perception, and eventually leads to acrophobia and/or photophobia, suggesting a potentially higher stress level associated with the behavioral responses of individuals with albinism to external stimuli compared to their pigmented conspecifics. However, in fish, differences in behavioral and/or physiological responses and stress levels between these phenotypes have been poorly documented. While acoustic perception of albino individuals is well known, the use of olfactory sensors for social communication, e.g., for the preference for familiar conspecifics, remains poorly understood. We performed two laboratory experiments with albino and pigmented European catfish Silurus glanis to observe: i) their behavioral and physiological responses to short-term stress induced by a combination of air exposure and novel environmental stressors and ii) their ability to use odor keys to recognize of familiar conspecifics and the influence of lateralization on this preference. In response to stress stimuli, albino fish showed higher movement activities and ventilatory frequencies and more often changed their swimming directions compared to their pigmented conspecifics. Blood plasma analysis showed significantly higher values of stress-, deprivation-, and emotional arousal-associated substances, e.g., glucose and lactate, as well as of substances released during intensive muscle activity of hyperventilation and tissue hypoxia, e.g., hemoglobin, mean corpuscular hemoglobin, erythrocytes, and neutrophil granulocytes. A preference test between environments with and without scented water showed the preference by both albino and pigmented catfish for environments with scent of familiar conspecifics, and both groups of fish displayed left-side lateralization associated with the observation of conspecifics and group coordination. The results tended to show higher physiological and behavioral responses of albinos to stress stimuli compared to the responses of their pigmented conspecifics, but the uses of olfactory sensors and lateralization were not differentiated between the two groups.

Harvest Rates of Rheophilic Fish Vimba vimba, Chondrostoma nasus, and Barbus barbus Have a Strong Relationship with Restocking Rates and Harvest Rates of Their Predator Silurus glanis in Lowland Mesotrophic Rivers in Central Europe

The European catfish Silurus glanis (Linnaeus, 1758) is an expanding apex piscivorous predator whose predation may drive fish harvest rates and fish populations. This study aimed to analyze the relationships between intensive catfish stocking/harvesting and harvest rates of putative catfish prey–three rheophilic fish species: vimba bream Vimba vimba, nase Chondrostoma nasus, and barbel Barbus barbus (Linnaeus, 1758). The GAM (generalized additive model) was used to analyze the relationships between the harvest rate and the stocking intensity rate of the catfish and the three rheophilic fish species. The harvest rates and stocking intensity rates were obtained from mandatory angling logbooks collected from 38,000 individual recreational anglers by the Czech Fishing Union on 176 fishing sites over the years 2005–2017 in central Bohemia and Prague (the Czech Republic). Our results show that a higher intensity of catfish stocking and harvesting resulted in a lower harvest rate of rheophilic fishes. Conversely, the stocking rates of rheophilic fishes were not significantly correlated to their harvest rates. In conclusion, a significant negative relationship was found between the harvest rate and the restocking rates of rheophilic fishes and their predator, suggesting that fisheries managers should not perform intensive stocking of both catfish and rheophilic fishes on the same rivers.

Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive Silurus glanis L. in a Deep, Large, and Oligotrophic Lake (Lake Maggiore, North Italy)

The ecological features of invasive alien species are crucial for their effective management. However, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore, where the species is present since 1990, but no scientific information is available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. The NPUE and BPUE (individuals (N) and biomass (B, in grams) per unit effort (m2), respectively) of catfish were generally higher in littoral (NPUE > 0.01; BPUE > 96) than in pelagic habitats (NPUE < 0.009; BPUE < 114), but the catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded, belonging to 12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad, and roach), whilst the diet of littoral catfish was more variable and dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.

A nitrogen factor for European pike-perch (Sander lucioperca), northern pike (Esox lucius), and sheatfish (Silurus glanis) fillets

Measures for consumer protection against food adulteration and misleading labeling are integrated into EU legislation, including methods for detection of misleading practices. Verification of meat content is available for marine products but not for freshwater fish because of the lack of standard nitrogen factors. The aim of this study was to establish nitrogen factors for European pike-perch Sander lucioperca (Linnaeus, 1758), northern pike Esox lucius Linnaeus, 1758, and sheatfish Silurus glanis Linnaeus, 1758. The study involved analysis of 808 fillet samples obtained in spring (March–April) and autumn (October–November) harvest seasons, 2018–2019, from seven Czech Republic fish rearing facilities. Samples with and without skin were analyzed for nitrogen content, dry matter, protein, ash, and fat according to established ISO methods. The recommended nitrogen factor for European pike-perch with the skin is 3.28 ± 0.09 and without the skin is 3.21 ± 0.09; for northern pike with the skin is 3.18 ± 0.09 and without skin is 3.15 ± 0.09; and for sheatfish with skin is 2.73 ± 0.13 and without skin is 2.75 ± 0.12. The established nitrogen factors will enable analysis of meat content to ensure that consumers are purchasing correctly described and labeled fish products.

A confirmed record of the European catfish Silurus glanis L., 1758 (Actinopterygii: Siluriformes: Siluridae) from the southern marshes of Iraq, with a new anatomical set of characters to separate S. glanis and S. triostegus

Investigations conducted in the southern Iraq freshwater systems allowed the authors to collect the European catfish, Silurus glanis L., 1758. These are the first confirmed records of S. glanis from the freshwater systems in Lower Mesopotamia, based on 13 adult specimens, each 325–525 mm in total length. Furthermore, a new set of anatomical characters of S. glanis and S. triostegus from Chibayish marsh area, south of Iraq, was examined to reveal similarities and differences between the two Silurus species. In addition to the traditional separation of the two species of Silurus by number of barbels, these two species can now be recognised based on a new set of morphological and osteological features.

Records of Invasive European Catfish Silurus Glanis (Linnaeus, 1758) in the Neretva River Delta (Croatia): Social Media as Information Source

Abstract Records of European catfish Silurus glanis in the Neretva River delta (Adriatic Sea basin) in Croatia are reported. The first occurrence of this non-native species was reported via social network which led to its timely detection by researchers. Origin of introduction is unknown but it is most likely the case of human-mediated introduction. The importance of social networks as a useful tool for the timely detection of non-native fish species, as well as the importance of raising awareness about the impacts of biological invasions, is discussed in this paper.

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 LB) 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.

Risk of invasiveness of non-native aquatic species in the eastern Mediterranean region under current and projected climate conditions

Human-induced biological introductions pose a major threat to global biodiversity, and this is especially frequent in the eastern Mediterranean region, which is a globally important biodiversity hotspot area of high conservation value. To predict at which level introduced species in this region might become invasive under current and projected climate conditions, 232 non-native aquatic organisms were screened using the Aquatic Species Invasiveness Screening Kit. Based on receiver operative characteristic curve analysis, thresholds were identified to distinguish between low, medium and high risk species. The “top invasive” (very high risk) species identified were: brown bullhead Ameiurus nebulosus, blue crab Callinectes sapidus, gibel carp Carassius gibelio, Philippine catfish Clarias batrachus, Chinese mitten crab Eriocheir sinensis, bluespotted cornetfish Fistularia commersonii, silver carp Hypophthalmichthys molitrix, silver-cheeked toadfish Lagocephalus sceleratus, half-smooth golden pufferfish Lagocephalus spadiceus, Suez pufferfish Lagocephalus suezensis, signal crayfish Pacifastacus leniusculus, fathead minnow Pimephales promelas, channeled applesnail Pomacea canaliculata, red swamp crayfish Procambarus clarkii, devil firefish Pterois miles and European catfish Silurus glanis. The risk of being invasive of more than half of the screened species increased after taking global warming predictions into account, and several species considered to be globally invasive (cf. high risk) were classified as posing only a medium risk for the eastern Mediterranean region. Region-specific risk screenings, as implemented in this study, are therefore essential for setting priorities in preventative management for the conservation of key biodiversity hotspots and the optimal allocation of resources in view of full risk assessment for the species identified as (very) high risk.

“The giants’ feast”: predation of the large introduced European catfish on spawning migrating allis shads

European catfish Silurus glanis is a large non-native opportunistic predator able to develop hunting strategy in response to newly available prey where it has been introduced. Migrating spawning anadromous prey such as allis shad Alosa alosa could represent this available and energy-rich food resource. Here, we report an impressive catfish hunting behavior on shad spawning act in one of the main spawning grounds in Europe (Garonne River, Southwest France). Shad spawning act consists of at least one male and one female swimming side by side, trashing the water surface with their tail which, therefore, produces a splashing noise audible from the river bank. The catfish hunting behavior on shad spawning act was studied, at night, during spring months, using both auditory and video survey. Simultaneously, catfish individuals were fishing to analyze their stomach content. Catfish disturbed 12% of the 1024 nocturnal spawning acts we heard, and this proportion increased to 37% among the 129 spawning acts when estimated with low-light camera recording. Stomach content analyses on 251 large catfish individuals (body length > 128 cm) caught in the same river stretch revealed shad represented 88.5% of identified prey items in catfish diet. This work demonstrates that European catfish predation must be considered as a significant factor of mortality of allis shad. In a context of the extension of the European catfish range area in western and southern European freshwaters, this new trophic impact, with other ones previously described for salmon or lamprey, has to be considered in European conservation plans of anadromous species.

Behavioural and fitness effects of translocation to a novel environment: Whole-lake experiments in two aquatic top predators.

Translocation into a novel environment through common fisheries management practices, such as fish stocking, provides opportunities to study behavioural and fitness impacts of translocations at realistic ecological scales. The process of stocking, as well as the unfamiliarity with novel ecological conditions and the interactions with resident fish may affect translocated individuals, leading to alterations of behaviours and causing fitness impacts. Our objectives were to investigate how aquatic top predators behaviourally establish themselves and compete with resident individuals following introduction in a novel lake environment and to investigate the resulting fitness consequences. Using high-resolution acoustic telemetry, we conducted whole-lake experiments and compared the activity, activity-space size and fate of translocated and resident individuals in two model top predators, the northern pike Esox lucius (n=160) and European catfish Silurus glanis (n=33). Additionally, we compared the reproductive success of translocated and resident northern pike. The experiment was conducted with large (adult) individuals of different origins, resilient to predation, but subject to agonistic interactions and competition with resident fish. Over a period of several months, the translocated catfish exhibited consistently larger activity-space sizes than resident catfish, but did not differ from residents in activity and survival. The pike from one of the two translocated origins we tested also showed elevated space-use, and both translocated origins revealed higher mortality rates than their resident conspecifics, indicating maladjustment to their novel environment. When non-resident pike reproduced, they overwhelmingly produced hybrid offspring with resident fish, indicating that introductions fostered gene flow of non-native genes. Our study indicates that fish introductions result in behavioural and fitness impacts even in large-bodied top predators that experience low levels of natural predation risk.