Invasive Species Fish

Topmouth Gudgeon  Pseudorasbora parva


Description and Identification
Topmouth gudgeon are usually 2 to 7.5cm in length, rarely above 8cm. All their fins are rounded and the dorsal fin origin is directly above the pelvic fins. They have an upturned lower jaw with a hard edge, no barbels. The males are usually darker in colour compared to females. This species can be confused with a number of juvenile native species although their appearance is quite distinct.

Problems caused
Topmouth gudgeon are a multiple spawning, nest building species. They are very prolific breeders, able to reproduce several times a year and can mature by the age of one.
This invasive species is an effective coloniser of waters into which its been released. When niches overlap with native species they are likely to out-compete native populations and become the dominant species in size classes of under 70mm. They may cause recruitment failure of native species by inhibiting breeding. They may also transfer novel diseases into the ecosystem.
Originally from Asia, populations are now present across England and Wales. Established populations are apparent across most of Europe.
Control measures
Topmouth gudgeon are listed on the Prohibition of Keeping or Release of Live Fish Orders and as such cannot be released into the wild without a licence. The Environment Agency has undertaken control programmes to eradicate Topmouth Gudgeon from specific lengths of effected river.
Actions that the public can take
Report their findings to the Environment Agency or Essex Biodiversity project.
Sources of information and References
National Fisheries Laboratory / Environment Agency
General Enquiries 08708 506 506.