Big problems come in small packages

Topmouth gudgeon is an invasive species of fish which is becoming an increasing concern for freshwater habitats across Europe. Native to East Asia the species can be found in Japan, China, Korea and the River Amur catchment. In 1990, the fish was first recorded in the wild in Hampshire, believed to have escaped from an introduced ornamental population.

So what makes this fish so invasive?

Topmouth gudgeon has several life histories traits which have facilitated its dispersal and spread across continentalEurope.

1. Early sexual maturity – These fish reach sexual maturity after just one year increasing the reproductive potential of the population
2. Batch spawning and nest guarding - Most Cyprinid species spawn thousands of eggs once a year. Topmouth gudgeon produce several batches of eggs between April and July, each of which are guarded by a male increasing their chances of survival.
3. Ability to spawn onto smooth surfaces – Unlike some fish species which are highly restricted on where they can spawn, the topmouth gudgeon can lay eggs on a variety of surfaces including smooth surfaces. This means the fish can spawn onto many artificial structures such as boat hulls and fishing equipment, increasing the risk of accidental transfer between water bodies
4. Small adult size – Being small, the natural dispersal of this species is swift, enabling populations to quickly escape and colonise new areas.

We o’fishally have a problem!

As well as being excellent dispersers, breeders and invaders, it is becomingly increasingly clear that this fish could have serious consequences for our native species and our fishing industry. Studies have found that the presence of topmouth gudgeon reduces native fish populations, out-competing them for food and spawning space. This competition also leads to our native fish having stunted growth!  However, the biggest concern is the fact that topmouth gudgeon is the healthy host of several fish parasites including Anguillicola crassus and Clinostomum complanatum.

Is there any hope?

In 2005, the species was recorded at 25 sites across England and Wales. This limited and isolated distribution gives conservationists a real chance at eradicating this species before any serious damage can be caused – so its really important that these fish remain in their plaice – we don’t want them spreading any further!

There have been successful eradication programmes of topmouth gudgeon however these are limited to isolated water bodies where a complete drainage of the lake has been achievable. Draining an entire river system would be impossible and therefore the prevention of further spread is crucial!

Let’s hope we can topmouth gudgeon out of our river systems – fins crossed?

References

Britton, J. B., Davies, G. D., & Harrod, C (2010). Trophic interactions and consequent impacts of the invasive fish in a native aquatic food web: a field investigation in theUK. Biological Invasions 12: 1533-1542

Gozlan, R. E., Pinder, A. C., & Shelley, J (2002). Occurrence of the Asiatic cyprinid Pseudorasbora parva inEngland. Journal of Fish Biology 60:

Pinder, A. C., & Gozlan, R. E (2005). Dispersal of the invasive topmouth gudgeon in theUK: a vector for emergent infectious disease. Fisheries

http://www.bbc.co.uk/news/uk-wales-south-west-wales-21227831

Photo Credits: Topmouth Gudgeon (both Matt Brazier, Environment Agency)