Weird fish of the week: Brook lamprey

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Lampreys have a fearsome reputation as razor-toothed parasites intent on sucking every last drop of blood from whatever unsuspecting fish they latch onto, but the Brook lamprey's feeding habits go against the image of its bloodsucking brethren.

The Brook lamprey (Lampetra planeri) is a small, eel like fish growing to little more than 15cm/6" in length. They are secretive creatures, seldom seen during daylight outside the spawning season.

They are extremely primitive fish, (with some questioning whether they are fish at all), with green-brown scaleless bodies that lack any of the paired fins typical in more 'normal' fish.

Other oddities include a cartilaginous skeleton and a line of seven holes just behind the eye supplying water to the gills.

If you are fortunate enough to live next to a suitably clean and clear stream you may spot them in the spring, breeding.

Like all lampreys they lack jaws, instead possessing a sucker, and it's with this that the spawning adults move aside stones and pebbles up to twice their own body weight in an effort to prepare the ideal spawning site of fine sand and gravel in which to deposit their eggs.

The scientific name for their family, Petromyzontidae refers to this specialised mouth, roughly translating as 'stone suckling teeth' in Greek.

Quite large groups can sometimes be discovered  busily 'nest' building and spawning together in a tangled mass, apparently oblivious to everything else as the females lay around 1500 eggs each.

The adults do possess teeth, but these are there to assist with adhesion to rocks as the adult fish do not feed and die shortly after spawning. The fascinating life cycle of these archaic creatures now starts anew, with the young, known as ammocoetes, hatching after about a month.

These strange eyeless juveniles lack their parents' sucker mouth, so are washed downstream to slower moving areas where they settle in silt or mud on the river bottom and dig a burrow. It's here they'll spend anything up to the next seven years as filter feeders until they undergo the metamorphosis into adulthood and repeat their ancestors' upstream breeding migration.

Despite being the UK's most common and widespread lamprey, the species is in decline with degradation of habitat the most likely cause. The Brook lamprey is also captured for use as bait in fishing for species such as Pike, Perch and Chubb. They are also resident in much of mainland Europe.

Check out the video below.

We covered the Sea lamprey (Petromyzon marinus) earlier in this series.

Why not take a look at some of our other Weird fish of the week features?

Barreleye 

Mega mouth shark

Flying gurnard

Pinecone fish

Slender snipe eel

Tripod fish

Lumpsucker

Ocean sunfish

Two-headed arowana

Stargazers

Giant oarfish

Kroyer's deep sea anglerfish

Halimeda ghost pipefish

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