What are lampreys?
Lampreys must be amongst the most rarely seen and poorly understood of all the fish species found in Scottish rivers. Their fossil remains show that they were around long before the dinosaurs and many familiar plant groups. There are three species of lampreys in Scotland: the brook, river and sea lamprey. They all belong to a group of animals called 'Agnatha' (meaning 'without jaws') which is the most primitive group of all living vertebrate animals. As the name suggests, lampreys lack jaws and instead have very primitive mouthparts surrounded by a large flexible lip that acts as a sucker. This curious feature provides the scientific name for the lamprey family, Petromyzonidae, which literally translates as 'stone suckers'.
Lampreys resemble eels but have several unusual features not seen in most other fish. Instead of bones, they have a skeleton of cartilage. Lampreys also lack scales, and have a single nostril located on the top of the head in front of the eyes. They do not have gill covers but do have a series of seven sac-like gills which open directly through holes on each side of the head. All lampreys have a long, cylindrical body, like that of eels.
The sea lamprey is by far the largest of the three species with adults reaching a length of one meter and weighing up to 2.5kg. Adult sea lampreys are a brownish-grey colour with extensive black mottling, but close to breeding time their colour lightens to a golden brown. The river and brook lampreys, which are closely related to one another, are far smaller. They are both similar in colour, with adults having a dark olive or brown back and a lighter, silvery belly. The river lamprey is intermediate in size between the other two species with adults usually measuring around 30cm and weighing about 60g. Brook lampreys are the smallest with adults only attaining a length of 15cm, yet there are even smaller dwarf populations with adults from one such population on the Isle of Skye often measuring less than 10cm.