Monday, November 28

We have just caught a 2.67 meter catfish in Zaragoza. That’s the least of our problems

A catfish of 2.67 meters has been captured in the Ebro river as it passes through Zaragoza, a record with a dark side: the catfish is an invasive species and a voracious predator of native fauna, a fish that simply should not be there.

The visible face of a serious problem. The catfish (Silurus glanis) is a freshwater fish, native to Eastern Europe, Central Asia and Asia Minor. It is capable of exceeding two meters in length and weighing one hundred kilos and is easily recognizable for its lack of scales and, more than anything, for its “whiskers”, actually called perioral barbels. The Ebro is not the only Spanish river in which this species has been found, but it has also been found in rivers as diverse as the Guadalquivir or the Llobregat.

As explained in the Spanish Catalog of Invasive Alien Species, this fish was introduced for sport fishing, a fact that has resulted in negative ecological and socioeconomic impacts. The catfish is a predator that feeds on native species, especially fish and invertebrates, but also amphibians, rodents and waterfowl. This voracity affects the resources of the native fishermen of the areas that it “colonizes”.

A wide range of damage. The damage caused by invasive species is perceptible and there are different studies that have tried to quantify it. According to data from the European Commission from 2013, invasive species caused annual damage worth 12,000 million Euros. Another more recent study, published in the journal Nature, estimated annual damage of more than 160,000 million dollars per year in 2017, with an average of 26,800 million euros per year between 1970 and 2017.

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In Spain, the cost of dealing with these species has also been calculated: 261 million dollars between 1997 and 2022. The study explains that most of the expenditure associated with invasive species is linked to management costs. The economic damages were minor, but they also clarify that extrapolated costs, expected costs and those considered to be of low reliability were excluded from the calculation. That is, it is a conservative estimate of costs.

What is an invasive species? The law defines invasive species as “the one that is introduced or established in an ecosystem or natural habitat (…) and that is an agent of change and a threat to native biological diversity (…) due to its invasive behavior, or due to the risk of genetic contamination. Based on this law, a catalog of invasive species was created in order to control them as much as possible.

Invasive species cover a very broad spectrum, from plants and algae such as Pampas grass (Cortaderia spp.) or the killer algae (Caulerpa taxifolia); even mammals like the raccoon (procyon lotor) or the American mink (Mustela (Neovison) mink). Some of these species are known to cause severe impacts.


An increasingly common problem. An example of this is the tiger mosquito (Aedes albopictus), transmitter of diseases such as malaria, Chicungunya virus or West Nile virus.

The zebra mussel is another of the species that is often heard about, since it has a strong impact on ecosystems, displacing native species; and is capable of clogging infrastructures such as pipes, filters, tanks or turbines; in addition to being able to negatively affect tourism.

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The red, American or mudflat crab (Procambarus clarkii) is also an old acquaintance. Among the damages attributed to it are ecological (destruction of vegetation or the displacement of native crabs), economic (damaging rice crops) and health (since it accumulates heavy metals and is a carrier of microorganisms that cause diseases such as tularemia or aphanomycosis).

Some of these species, such as the tiger mosquito, the killer algae, the Argentine ant (Linepithema humile), or the common rat (rattus rattus) among others, are on the list of the most harmful invasive species in the world.

What to do against invasive species. When it comes to avoiding this problem, prevention is the first measure that administrations must take. Not all alien species are able to survive and take root in a new ecosystem, and not all of those that do are harmful (some are even beneficial to the ecosystem and/or the economy). Identifying potentially dangerous species is an important first step. Once the species have become established, it is necessary to catalog them to assess the damage and design plans for their eradication, such as the Spanish Catalog of Invasive Alien Species. In case of not being able to eradicate a species, it may be necessary to mitigate its damage and adapt to the new situation.

At the individual level, action is also possible. If we come across an invasive species, the recommendation is to inform the environmental authority of the corresponding Autonomous Community. Some of the species included in the catalog are pets, which must be registered with the competent authority, although the main recommendation is not to acquire them. Going to the veterinarian frequently and knowing the characteristics of the pet before acquiring it are also among the recommendations of the Ministry of Ecological Transition, as well as not abandoning it in the natural environment.

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Image | Fisherman poses with a fish from the Siluridae family, a distant cousin of the one caught in the Ebro. Clenex on Pixabay

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