European fish endangered by invasive species, pathogen infection found to be the cause

A 2005 study done by researchers at the Centre for Ecology and Hydrology in England shows just how dangerous introducing invasive species can be. Rodolphe Gozlan and his colleagues studied how and why the population of the native European sunbleak (Leucaspius delineatus) decreased throughout European rivers. This fish was once commonly found in the continent’s rivers but is now threatened with extinction.

The reason?

Gozlan’s team found that a parasite (S. destruens) found in healthy fish species of Pseudorasbora parva is easily transmitted to the sunbleak. P. parva was introduced from Asia to Romanian ponds fifty years ago and has since found its way into the European river system. The foreign fish species is now widespread, and in some regions, has indirectly killed all local European sunbleaks. Lab experiments performed by Gozlan et. al. had populations of both species of fish placed in outdoor ponds and observed over three years. While the pond containing only sunbleaks showed normal spawning and death rates, the pond containing both species caused the sunbleaks to lose the ability to spawn. Three seasons later, 96% of the sunbleaks had died.

Upon examining several sunbleaks after death, it was found that they had suffered massive internal infections. In addition, their reproductive organs could no longer function because of the pathogen. These infections were shown to have been caused by the same pathogen present in P. parva.

What is possibly more alarming is that the European sunbleak may not be the only species of fish that may be affected by the parasites harboured by P. parva. The study suggests that other salmon-like fish species (cyprinids) may be vulnerable to the pathogen. Atlantic salmon and Chinook salmon have been shown to be susceptible to infection as well. P. parva has now become the most numerous and invasive fish species in Europe, and the fact that it carries a potentially deadly parasite does not bode well for European marine biodiversity.

In fact, the potential decrease in biodiversity is not the only concern. It has been found that it is challenging to find out which members of a sunbleak population may be infected. Testing a fish for the presence of the parasite is an extensive process, and even then, only two-thirds of the sunbleaks tested were found to be carriers. This may seem like it is to be expected, but Gozlan et. al. found that 28% of the sunbleaks who were not exposed to P. parva already carried the parasite! In addition, there may now be other, completely different, species of fish that could be infected with S. destruens, but are immune to its effects. This would only serve to magnify the ill effects on the cyprinid caused by sharing the same parasite-infected rivers and lakes.

There is also another problem raised by the introduction of S. destruens in European waters. As a result of the sunbleak and other fish not being able to spawn, and in some cases dying early, European fisheries are in danger. Since Atlantic salmon (the main salmon farmed in Europe) are vulnerable to the parasite, should commercial salmon farms become infected it will be a big hit to the fishing industry and trade in the European coastal countries.

The effects of introducing foreign invasive species are not just limited to European lakes and rivers. Over the past several hundred years, humans have travelled across the world bringing with them species native from where they came. Even something as comparatively small as a bacteria can have devastating effects. One has to look no further than when the Europeans arrived in the Americas, bringing diseases that they were immune to to the Native population. Millions of First Nations people died because they were not immune to the viruses and bacteria that the Europeans introduced into their environment.

Now that most people in the developed world can travel globally, it is important that we reduce the number of non-native organisms that are introduced to other regions. The world’s ecosystems have developed over thousands and thousands of years, and each species fills a niche in it. Often times, human activity is based on these ecosystems. When foreign organisms are introduced, it has the potential to disrupt the environmental balance that has been evolved over a long period of time. This will serve to have only negative consequences for all species involved, including us.

Works Cited

Journal article:

Gozlan, Rodolphe E., Sophie St-Hilaire, Stephen W. Feist, Paul Martin, and Michael L. Kent. "Biodiversity: Disease threat to European fish."Nature 435 (2005): 1046.Biodiversity: Disease threat to European fish. Web. 12 Oct. 2010.

Other:

Harris, Todney. "09.05.03: Introduction to the Diseases of Smallpox, Measles and Influenza and the Effects on the Indigenous Populations on the Continent of North America." Yale University. N.p., 3 May 2009. Web. 13 Oct. 2010. .