Catfish boom threatens salmon reintroduction in Baden-Württemberg waterways

Rapid expansion

Catfish, the largest native freshwater fish in Europe, are spreading quickly through rivers, lakes and even isolated gravel pits across Baden-Württemberg. Alexander Brinker, head of the fisheries research station in Langenargen, reports that the share of rivers in the state where the species has been detected has nearly tripled over the past 20 to 40 years. The animal is highly adaptable and benefits directly from warmer water, which accelerates its growth and reproduction.

The migratory fish, which are very, very heavily threatened, often pass through bottlenecks like fish ladders. And the catfish is very good at positioning itself at these bottlenecks and eating the migratory fish there.

Lake Constance catch data

Data from Lake Constance illustrates the scale of the increase. Until 1990 the annual catfish catch was around 100 kilograms. By 2020 that figure had reached 4.5 tonnes, and by 2024 it had climbed to nearly 8 tonnes. Over the same period the measured surface temperature of the lake rose from about 11-12 degrees Celsius to 13-14 degrees.

Threat to salmon reintroduction

The Landesfischereiverband Baden-Württemberg runs a programme to re-establish salmon in the state’s waters, but catfish are undermining that effort. At a fish ladder on the Kinzig river in the Ortenau district, catfish lie in wait to ambush migrating salmon. Ingo Kramer, managing director of the association, says the losses and injuries are significant.

We are seeing both significant losses of salmon there, as well as injuries to the salmon.

The Ministry of Agriculture describes the catfish as a top predator that grows quickly and, in good conditions, can exceed a metre in length. Large specimens occasionally take waterfowl, but their main prey are other fish and crustaceans.

Climate driver

Both scientists and fishery managers point to climate change as the main force behind the catfish’s success. Rising water temperatures create ideal conditions for the species, allowing it to out-compete many native fish. Kramer calls the catfish the principal profiteer of the changing climate.

We are simply observing that catfish, as the main beneficiaries of climate change, are multiplying very rapidly.

Brinker notes that the species already inhabits not only the Rhine, Neckar and Lake Constance, but also smaller and isolated water bodies across the south-west. Without intervention, the pressure on threatened migratory species and the wider aquatic ecosystem is expected to grow.