SCIENTISTS have made the first conclusive sighting of a fish species never before recorded in Windermere.

DNA surveys carried out in 2015 inferred that ruffe were to be found in the lake but a single individual has now been discovered.

Ruffe, a relative of the more familiar perch, is not native to the lake but has specific traits that mean it can thrive if introduced to new habitats.

A single individual was found when scientist Ben James and colleagues examined catches from the Centre for Ecology and Hydrology’s long-term fish community monitoring last month.

Ruffe have been recorded at Bassenthwaite Lake, Derwent Water and Thirlmere, also beyond their native species range, but are absent from many of the other larger Lake District water bodies.

It is unclear whether the species was introduced into Windermere directly, possibly following their use as live bait by anglers, or whether it reached the lake from Rydal Water three kilometres upstream, where ruffe were previously introduced.

Dr Stephen Thackeray, Lake Ecosystems Group Leader at the Centre for Ecology & Hydrology (CEH), said: "We do not yet know the current size of the Windermere population.

"It could be present in low numbers and further work would need to be done to determine this.

"However, ruffe are suited to successfully colonising new habitats: they can tolerate a wide range of water temperatures and chemical conditions; they feed on a variety of small fish and invertebrate prey and they can spawn at an early age and more than once a year.

"All of this translates into the potential for rapid population growth. Ruffe are also known to feed on the eggs and larvae of other fish, which may be a cause for concern."

This latest finding follows years of decline in the Windermere Arctic charr populations, as well as increases in non-native roach in the late 1990s and, more recently, increases in non-native bream.

Dr Thackeray added, “It is clear that the Windermere fish community is undergoing change, and that there is a need for continued vigilance if we are to understand the impacts of these changes on the wider ecosystem.”