A new deadly disease, carried by an invasive fish species, is threatening European fish diversity according to a paper published in the journal Nature on 23 June 2005.

Lead author Rodolphe Gozlan from the Centre for Ecology & Hydrology (CEH) said: “We have found a parasite that may pose a severe threat to some freshwater fish species in Europe. This discovery has major biological implications and may have economic implications.”

The scientists working for CEH and the Centre for the Environment, Fisheries & Aquaculture Science (CEFAS) have found an infectious disease carried by the topmouth gudgeon – the most invasive fish species in Europe. The disease stops the European sunbleak, an endangered species in mainland Europe (although not native to the UK), from spawning – leading to its rapid decline and possible eventual extinction.

The scientists blame the disease for the rapid demise of the sunbleak in parts of Europe following the spread of the Asian topmouth gudgeon. “The new disease is already affecting other freshwater fish such as the fathead minnow and may affect native UK fish species,” added Dr Gozlan.

But the researchers, funded by Natural Environment Research Council and Defra, found that the parasite does not harm the topmouth gudgeon.

Dr  Gozlan said: “The topmouth gudgeon is a healthy host for this deadly parasite.’

‘This parasite could threaten commercial fisheries, including salmon farms,”

he went on to say.

The researchers believe the parasite is closely related to Rosette Agent, identified in the United States for the first time in 1986, which kills salmon and similar species, both farmed and wild. Work is in progress to determine any differences between the present parasite and Rosette Agent.

The scientists say more work is required to determine the extent of the threat to European fish diversity, but have observed that sunbleak populations have declined dramatically in the last forty years and the species is now on the European list of threatened freshwater fishes. This decline coincides with the rise in numbers of the topmouth gudgeon and its rapid spread throughout Europe since its introduction into Romanian ponds close to the river Danube in the 1960s.

Topmouth Gudgeon have been recorded in several rivers and lakes in England and Wales.