UK lakes poisoned to counter invasive Japanese Topmouth gudgeon threat

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Disease carrying invasive Gudgeon are causing major problems in British waterways, leading to drastic action of the part of the Environmental Agency, reports Nathan Hill.

A Hampshire fishery is taking extreme measures to counter the spread of disease and eradicate the highly invasive Japanese Topmouth gudgeon by poisoning several of its lakes.

The ILFA listed fish, illegal to buy or own without the appropriate licence, has been found at the FLE fishery in Hampshire.

The lakes will be trawled for as many native species as possible before poisonous piscicide Rotenone is added, killing any fish that remain.

Topmouth Gudgeon, Pseudorasbora parva, is a Cyprinid that came to the UK during the 80s, when it was introduced alongside other imported species.

Escapees have caused massive damage throughout the UK, as the fish outcompetes with indigenous species for food, as well as eating rivals’ eggs and larvae.

The Environment Agency claims that the fish is a “significant threat” to the region despite its small size. In entering local waterways the potential to cause ecological havoc is great.

The FLE lakes are not connected to local river systems, but the Environment Agency’s concern is that the Topmouth gudgeon population could spread if left unchecked.

Should the fish find their way into waters inhabited by Salmon, the devastation could be huge.

A major concern of the Environment Agency is that Topmouth gudgeon host the deadly Rosette agent parasite, Sphaerothecum destruens. The disease causes huge morbidity and mortality amongst salmonids.

Other fish such as Carp, Roach and Bream are also affected by the parasite.

Critics of the operation point out that Rotenone can linger in waterways for weeks or even months, though this is unsupported by data. Generally, Rotenone will degrade within days when exposed to sunlight, and by the interaction of soil and water.

The cull highlights the dangers of placing non-native fish into the wild. Although these are not aquarium species the situation is a stark reminder that illegally released fish can cause massive damage to ponds and lakes.