Invasive fish disrupts French ecosystems

The pseudorasbora, also known as the Asian gudgeon, is a small freshwater fish that has become a major threat to ecosystems in France. This species, originally from East Asia, has spread across the country since the late 1970s and is now found in many waterways, where it has caused significant ecological damage.

Origins and spread of the invasive species

The pseudorasbora was first introduced to Europe in the 1960s, when it was accidentally brought in with Chinese carp imports to Romania. From there, it spread through the Danube River and eventually reached France in the late 1970s. Since then, it has expanded its range gradually, becoming a well-established presence in several regions, including the Tarn basin.

Habitat preferences and ecological impact

The pseudorasbora thrives in calm or slow-moving waters such as ponds, canals, and floodplain areas with abundant vegetation. These conditions are common in regions with many fish farms and frequent exchanges of fry, which have facilitated its spread. The fish’s ability to adapt to a wide range of environments has made it a successful invader.

Hidden threat: the fungal parasite

What makes the pseudorasbora particularly dangerous is the fungal parasite it carries. This parasite infects other fish species without affecting the pseudorasbora itself, leading to severe population declines. In some affected areas, fish populations have dropped by as much as 80 to 90 percent in a short period.

Reproductive strength and competition

In addition to the parasite, the pseudorasbora’s rapid reproduction and broad diet put it in direct competition with local fish species for food and spawning areas. In some Mediterranean regions, 56 percent of fish species are now considered threatened, with 18 percent classified as critically endangered, showing the severe impact of this invasion.

Global significance and irony

The pseudorasbora is one of the few known invasive species that carries a pathogen capable of infecting a wide range of species. It spreads quickly, colonizing five new countries on average every decade. Despite its ecological damage, the fish has no commercial value in Europe and is used mainly as forage for other fish in aquaculture, highlighting the irony of its role as an ecological disruptor.

Ecosystem vulnerability and future concerns

The spread of the pseudorasbora underscores the fragility of aquatic ecosystems, where even a small, unnoticed species can cause widespread disruption. Practices such as restocking ponds, while beneficial for fish farming, have also facilitated the spread of invasive species. Today, managers are more cautious during fry transfers, but the question remains: how many other hidden invaders are still undetected?