Topmouth Gudgeon

First identified in the UK in 1984, Topmouth gudgeon is an extremely invasive species that has spread rapidly via fish farm movements and the ornamental fish trade. 23 populations have been identified across England.

The Environmental Agency began localised eradication efforts in 2004. As of 2017, there was only 6 confirmed sites remaining in England which are confined to the Midlands and South East England. This species disperses easily with females reaching sexual maturity rapidly and being high reproductive (thought to be around 4 times faster than native relatives). Lives in well-vegetated still waters including channels, ponds and lakes. They have a broad diet, predating on invertebrates and the eggs and larvae of native fish species. Topmouth gudgeon live in large, dense shoals with highly territorial males and are also carriers of several novel parasite species and disease that can be detrimental to native species and other non-natives including Sunbleak.

• Not present in Northern Ireland – Risk of introduction via aquatic trade and fish bait. Under the Invasive Alien Species Order 2019 it is an offence to intentionally keep, breed, transport to, from or within Northern Ireland, use or exchange Topmouth gudgeon or to release it into the environment.

• As this species is a prevalent carrier of many parasite and fungal disease, it is vital that biosecurity measures are fully assessed during survey design and implemented during sampling.