The lamprey, which evolved more than 360 million years ago and has barely changed since, is becoming more prevalent in the Great Ouse, Trent, Derwent, Wear and other rivers as man-made barriers are removed and water quality improves.
An eel-like fish with a jawless, circular mouth, some species of the adult lamprey attach themselves to the side of species such as trout, herring and even basking sharks and draw on their blood and body fluid until its host either dies or is left with a large wound.
Despite a repugnant appearance and – in some parts of the world – devastating effect on fish populations, the lamprey’s squid-like flesh was considered a delicacy by various kings and queens and features on menus in the Games of Thrones series.
Its revival has been hailed as a “symbol” of better water flowing through Britain’s rivers today.