A 400-million-year-old blood-sucking creature eaten by Vikings and a relic from the Ice Age top the Environment Agency’s new list of England’s rarest fish, with many of the ‘secret seven’ found in Cumbria.

The seven species are lamprey, Arctic charr, vendace, spined loach, allis shad, twaite shad and smelt.

All seven species of fish are a conservation priority, with reasons for their previous decline including historically poor water quality, barriers to migration and a changing climate.

But now, all seven are starting to thrive again thanks to work by the Environment Agency and other conservation groups.

Lampreys are eel-like creatures, once eaten by Vikings, and pre-date dinosaurs by more than 200 million years.

Thanks to the lowest levels of pollution seen for 100 years and the removal of barriers to their spawning migrations they are returning to many UK rivers.

Lamprey can be found in all our Cumbrian rivers, most notably in the Eden and Derwent where they are designated features of the Special Areas of Conservation.

The majority of UK Arctic charr populations are in decline with increasing temperatures considered to be one of the greatest threats to their existence.

In England they are native only to the Lake District where they are present in Windermere, Coniston Water, Wast Water, Buttermere, Crummock Water, Haweswater and Thirlmere.

In 2005, the Environment Agency, together with partners including the Forestry Commission, United Utilities and Wild Ennerdale, set about trying to reverse their decline in Ennerdale, with recent surveys showing that charr numbers there are increasing.

The herring-like vendace is the rarest native freshwater fish species in the UK. This silver fish is native to just two English lakes - Derwentwater and Bassenthwaite. The Environment Agency has been working with others to improve river habitats upstream of Derwentwater and to prevent the introduction of more non-native species that could harm the vendace.

While the populations in Derwentwater remain healthy, it is unclear whether or not the Bassenthwaite Lake population still exists – only one vendace has been found there since 2001.

Alastair Driver, Environment Agency national biodiversity manager, said: “These rare fish are unknown jewels of our rivers, lakes and coastline - the Environment Agency has a range of projects to support them and although England’s rivers are the healthiest for 20 years, there is still more to be done to improve their chances.

“Reintroducing meanders, breeding fish and removing weirs are among our key work to help these little-known fish thrive.”