Environment Agency successfully eradicates Top Mouth Gudgeon

An alien fish that threatened to wipe out the local fish population in two East Devon lakes and the River Otter has been successfully removed by the Environment Agency.

The Top Mouth Gudgeon was discovered in lakes at Bicton College and Bicton Park Botanical Gardens near East Budleigh in 2004. Measuring only 3 – 4 cms in length, the tiny invader out-competes native species and also carries a damaging parasite that can interfere with the breeding cycle of salmon and trout.

The Agency swung into action in 2006 after thousands of the gudgeon were washed into the Bicton Stream during a thunderstorm. A gravel filter was installed to prevent the invader from spreading, but the gudgeon were swept past the filter after the lake overflowed.

Agency fisheries officers removed around 6,000 of the fish from the stream following the thunderstorm ‘break-out.’ By acting swiftly, the Agency prevented the Top Mouth Gudgeon from moving downstream and colonising the Colaton Raleigh Stream which in turn flows into the River Otter.

But the battle was far from over. With an estimated 100,000 of the alien fish still in the smaller lake the local fish population was still under threat and there was a risk that, once again, the gudgeon would escape and spread into nearby rivers and streams.

It was decided the only solution was eradication. In March 2007 the Agency prepared for a final showdown with the tiny invader. Fisheries officers carried out a rescue operation and removed native species including carp from the two lakes. With the native fish safely re-located to temporary holding ponds, a piscicide (poison) was then used to eradicate the Top Mouth Gudgeon.

Rotenone is an environmentally safe piscicide that only targets fish and quickly breaks down in the environment. It doesn’t harm other aquatic life such as insects, mammals or birds.

Last autumn Agency fisheries officers electro-fished the lakes and Bicton Stream and could find no sign of the troublesome gudgeon. Today (April 21, 2008) officers will carry out a second survey of the area to confirm their earlier findings. This should demonstrate that the Top Mouth Gudgeon has finally met its match and is no longer wreaking havoc in two of East Devon’s most popular ornamental lakes.

‘The signs are very encouraging. We couldn’t find any Top Mouth Gudgeon when we carried out our first survey in October 2007. Instead, they’ve been replaced by a very healthy population of carp in the lakes. We have plans with Bicton College to introduce other species into the lake soon. In the meantime, we are doing a follow-up survey that hopefully will show the eradication has been successful,’ said Dave Brogden for the Environment Agency.