Brook lamprey

Lampetra planeri

SPECIES OF THE MONTH

November 2022

They are reclusive, primitive and eel-like; even if they look like one, they are not a fish. Instead, they belong to the superclass cyclostomi. Unlike some species of lamprey, the adults do not migrate to the sea and do not have a parasitic phase. Instead, they live most of their life as a larva buried in the silty stream bed before turning into an adult and swimming upstream to spawn.

Adult Brook Lamprey have a long, eel-like body and measure 15-25cm. They are greenish-grey with two dorsal fins, a single nostril on top of their head, and eight orifices arranged in a row on both flanks behind each eye. The orifices were first thought to be eyes, but actually, seven of the openings are gills, and the other is an olfactory organ.

They lack jaws, instead possessing a sucker that spawning adults use to move stones and pebbles when preparing the nest site. The scientific name for their family, Petromyzontidae, refers to this, roughly translating as ‘stone suckling teeth’ in Greek.

During spawning, the anal and mouth areas of the Brook Lamprey turn an orangey red.

Juvenile Brook Lamprey

Ammocoetes and transformers from a tributary of the River Boyne. The ammocoetes have not yet fully developed the sucker mouth, and are a brown/pink colour. The transformers can be seen attaching themselves to the sides of the tank.

The ammocoetes (larvae) are semi-translucent and grey-brown; however, some may have much-reduced pigment and appear golden.

Following metamorphosis, Brook Lamprey transformers turn more silvery along the sides, with their belly and back remaining dark grey-brown.

Unusual non-pigmented albino Brook Lamprey
Ammocoetes from the River Nire, Co Waterford
© Lampreysurveys.com

Lifecycle

Adults spawn in the shallow parts of streams from April to June once the water temperature is over 10–11°C. Both males and females work to build nests, using their sucker-like mouths to pick up rocks and create pits in the stream bed.

Several males mate with a female, and eggs are deposited into the nests. Within a month of spawning, the adults die.

Eggs hatch within a few days, and the young lamprey stays in the larval stage (known as an ammocoete) for around four to seven years. The larvae leave the nest at 3-5mm in length and drift downstream, settling in the silt or mud and where they dig a burrow.

Eventually, the young lamprey metamorphose into adults en masse in July and September and remain nocturnal and hidden to avoid predators. At this stage, they develop a primitive eye and a disk ring of ‘teeth’ but stop feeding entirely.

Distribution in Suffolk

Habitat

Brook Lamprey live in freshwater streams, rivers and, occasionally, lakes. They have exacting habitat requirements of gravel beds for spawning and soft marginal silts but with high levels of dissolved oxygen for the larvae. Sadly excess sediments from pollution can smother gravel riffles. In addition, the artificial straightening of river channels can disrupt the formation of gravel riffle and silt pool sequences. This means that whilst still relatively widespread, their numbers are declining.

Did you know?

A Brook Lamprey’s skeleton is made up of cartilage, not bone.

Diet

Brook Lamprey only feed as ammocoetes, filtering bacteria, algae, detritus and other organic matter from the water. Once they become an adult, their digestive functions stop, and they become unable to feed altogether.

Spotting Brook Lamprey

As they spend much of their time hiding in the sediment, it can be challenging to spot them. Therefore, the best time to try and find them is during the spawning season, in shallow areas of clean and clear brooks, streams and rivers.

If you are lucky enough to spot Brook Lamprey don't forget to record your sighting!

Created by:

Suffolk Biodiversity Information Service