Fish at risk from Clicker barb parasite

Europe's fish are at risk from a new parasite which may be present in populations of a non-native fish species.

According to research published today in the journal Nature, the Topmouth gudgeon, Pseudorasbora parva, which is better known to fishkeepers as the Clicker barb, carries a parasite which is capable of wiping out other species of fish.

The team of scientists behind the paper studied an introduced population of Clicker barbs in a European water and claim that an infectious "rosette-like intracellular eukaryotic parasite" apparently found on healthy barbs is a "deadly, non-specific agent".

They say that the parasite, which is probably carried by healthy Pseudorasbora parva, could decrease biodiversity and have implications for commercial aquaculture.

The study provides evidence to show that infected Topmouth gudgeon have already killed many endangered cyprinids, Leucaspius delineatus, in one water and have totally inhibited the fish from spawning.

"It could potentially spread everywhere... it could be quite devastating..."

Consequently, it could only be a matter of time before the parasite wipes out its host.

The researchers think that the disease studied may be similar to, or possibly the same, as a disease called "rosette agent" which is found in some US fish stocks.

Rosette agent affects salmonids, including trout, salmon and char. If the disease is present in UK populations of the fish it could be potentially dangerous to the country's fish farming industry, as well as to our native salmonid stocks.

Dr Rodolphe Gozlan, one of the authors, told The Scotsman: "DNA tests are now required to see whether it is the same as the US parasite.

"The rosette agent does affect salmon species, and it can survive in both fresh and sea water because it lives inside the cells of the fish. In the US it has been found in aquaculture about three times, and has killed the entire stocks in the pens.

"If it is the same as the one in the US, then we have a very successful healthy carrier of this deadly pathogen in the form of the topmouth gudgeon, and it could potentially spread everywhere ... it could be quite devastating."

In an interview with The Telegraph, Gozlan was reported as saying: "The new disease is already affecting other freshwater fish such as the fathead minnow and may affect native UK fish species.

The Topmouth gudgeon is regarded as one of the most invasive fish species and there are many feral populations in the UK and elsewhere in Europe.

It is illegal for dealers to stock or trade in this species, and fishkeepers are only able to keep the species with permission from Defra - permission which is unlikely to be granted, we suspect.

For more details on the parasite see the paper: Gozlan, RE., Sophie St-Hilaire, S., Feist, SW., Martin, P. and ML Kent (2005) - Biodiversity: Disease threat to European fish. Nature 435, 1046 (23 June 2005) doi: 10.1038/4351046a