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The catfish, a key player in the food chain
The wels catfish (Silurus glanis), often perceived as a threat to our rivers by those who don't study it, is in fact a major ecological player.
This giant is a super-predator whose role goes far beyond simply consuming prey: it structures and regulates aquatic ecosystems. Contrary to popular belief, its presence is not simply an imbalance, but can actually enhance biodiversity and support intermediate carnivores. As a super-predator, it is capable of influencing the entire food chain, and even helps to combat certain invasive species
The trophic role of a super-predator
A super-predator sits at the top of the food chain, exerting a decisive influence on the entire food web. The catfish is a perfect example of this function. By feeding on carp, bream and barbel, it limits the dominance of these species, which sometimes tend to dominate in terms of biomass. By reducing their ecological weight, they free up space for other, smaller species, thus diversifying the balance.
This regulation has a cascading effect, with forage fish such as roach and rotengill becoming more abundant as they face less competition. These small fish are an essential resource for carnivorous fish such as perch, pike-perch and pike. Thus, through its indirect action, catfish encourage the development of these predators and support the overall balance of the fish community.
Added to this is its health role, as it often targets weakened or sick individuals, helping to clean up prey populations and maintain their vitality.
Dietary plasticity for balance
All scientific studies show that the catfish is not limited to one type of prey, and that it demonstrates astonishing dietary plasticity. In Lac du Bourget, for example, recent analyses have revealed that they eat crayfish, perch and rotengles, as well as pelagic and benthic fish. Each individual adapts its diet to its environment, demonstrating a remarkable capacity for adaptation.
In Italy's Lake Maggiore, catfish also prey on exotic species such as American crayfish and Corbicula bivalves, helping to regulate invasive species that often disrupt ecosystems. This dietary diversity shows that catfish not only exploit the most abundant prey, but also integrate into the complex dynamics of the environment they occupy.
An ally against imbalances
Because it occupies a central position in the food chain, the sheatfish acts as a major ecological regulator. Its presence prevents the overpopulation of certain dominant species, favors the balance between forage fish and predators, and indirectly contributes to fish diversity.
Its action is reminiscent of that of large terrestrial predators, such as wolves in forests or meadows, whose role is not limited to predation, but extends to reorganizing the entire ecosystem. By its very presence, the sheatfish embodies this same principle of ecological cascade applied to the aquatic world.
Promoting the trophic cascade effect
A concrete example of this regulatory approach can be seen in Germany's Elbe basin. In certain sections of this river, wels catfish have even been voluntarily reintroduced to control the overpopulation of common bream, their main natural regulator. These releases have been carried out in areas where the catfish is indigenous but had declined sharply due to commercial fishing and pollution, in order to restore a natural balance.
Post-introduction observations show a noticeable regulation of the dominant cyprinid populations and a better availability of forage fish to the benefit of other carnivores, illustrating in concrete terms the cascade effect that catfish can have when they play their full ecological role.
Better understanding for better value
This essential function is at the heart of a European project called "LIFE PREDATOR", launched in 2022 for a five-year period with a budget of 2.85 million euros. Italy, Portugal and the Czech Republic are collaborating to study the impact of catfish on aquatic biodiversity.
Far from seeking to demonize the species, this program aims to better understand its role, measure its effects on ecosystems and provide management keys adapted to different contexts. This project underlines the fact that it is no longer appropriate to reduce the sheatfish to a simple threat. On the contrary, it represents an opportunity to reassess the role of super-predators in freshwater environments, and to reflect on their contribution to ecological resilience.
A role that depends on the environment
However, the picture needs to be qualified. The regulating role of sheatfish is highly dependent on the ecological context in which it evolves. In a large river rich in species and diverse habitats, its presence clearly helps to structure and energize fish communities. But in a more restricted and closed body of water, it can become too dominant and exert excessive pressure on available resources, especially in the first years of implantation, when the population explosion occurs even before it plays the role of regulator for its own species.
Finally, the composition of the initial population also influences their effects. Where cyprinids are overabundant, sheatfish act as an effective regulator, whereas in an already fragile environment, their impact can be more mixed. This variability shows that its influence is contextual and must be assessed on a case-by-case basis, without making generalizations one way or the other.
Overcoming prejudice
Far from being a destructive intruder, the wels catfish is above all an essential regulator of our aquatic environments. As a super-predator, it helps to limit the dominance of certain species, promote the development of carnivores, control invasive species and maintain healthy populations. However, its role is conditioned by the environment in which it settles, requiring detailed analysis to fully understand its impact.
Ongoing research and European projects such as LIFE PREDATOR remind us that it's time to overcome prejudice: the sheatfish is a key piece in the complex puzzle of aquatic biodiversity, whose presence deserves to be understood and valued rather than feared.
