What’s happening around Lake Balaton? Tropical fish are now biting people!
Researchers have warned of a growing ecological threat around Lake Balaton after several tropical fish species (some capable of biting humans!) were identified in the Hévíz Canal and, more worryingly, in colder waters further from the lake’s thermal source. Scientists say the rapid rise of non-native fish in Hungarian waters demands urgent attention.
A surge in exotic species
According to the Balaton Limnological Research Institute, 89 new fish species have appeared in Hungary in the past 24 years, bringing the total number of known non-native species and hybrids to around 130. Most of these newcomers are heat-loving aquarium fish, often introduced by private owners.
The Hévíz Canal, which carries the surplus warm water of Hévíz Lake towards Balaton and remains between 22 and 25°C year-round, has become a hotspot for exotic species. Among those now thriving are Yucatán mollies, lemon cichlids, firemouth cichlids and the predatory jaguar cichlid.
“These fish are most likely aquarium pets that have been released, or their offspring,” explained Péter Takács, senior research fellow at the Balaton Limnological Research Institute, in an interview with Turista Magazin. “Owners may have tired of them or no longer had space. They don’t want to kill them, and returning them isn’t an option. A buy-back or return scheme for unwanted aquarium pets could significantly improve the situation.”
From warm canals to colder habitats
While tropical fish are typically restricted to warm waters, experts are increasingly concerned that some species are starting to tolerate cooler conditions. Researchers have spotted several non-native fish in colder, more distant stretches of the canal, raising fears that certain populations may eventually adapt to Hungary’s climate and spread further.
The history of the mosquitofish (Gambusia holbrooki) illustrates this risk. Introduced worldwide, including to Hungary in the 1920s, for mosquito control, the species escaped into the wild and slowly advanced from the thermal canal into nearby ecosystems. “It took around a hundred years and nearly a hundred generations for them to reach the Kis-Balaton,” Takács noted.
Biting incidents and an aggressive newcomer
During winter, the canal is used by rowers, while in summer, swimmers often enter the water despite bathing being prohibited. So far, the small tropical fish “only nibble playfully” at people in the water, researchers say. However, recent findings suggest a far more serious threat may be emerging.
A few juvenile snakehead fish have been identified in the canal: an alarming development given that most species in this family are highly aggressive predators capable of devastating local fish populations. Snakeheads are strictly prohibited for sale in Hungary due to their potential ecological impact.
Growing ecological pressure
Although experts stress that a nationwide spread of warmwater species is unlikely in the short term, the long-term risk cannot be ignored. Given enough time, even heat-dependent species may develop cold-tolerant strains capable of surviving winters and reproducing in new habitats.
With the Balaton region already under environmental pressure, researchers are urging improved monitoring, stronger prevention measures and, crucially, a system for the safe return of unwanted aquarium fish.
“Every new introduction carries a risk,” Takács warned. “If we do nothing, we may face increasingly aggressive, ecologically harmful species in our waters.”