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Lancelets, lampreys and hagfish

This article explores something of the life of the world’s most primitive fish.

Sea Lamprey


Having been around for perhaps 500 million years, these are the most primitive species of fish, indeed some taxonomists argue they should not be classified as fish at all. They are marine dwelling and are found living in all of the main oceans. Around 30,000 kgs, roughly one billion lancelets are harvested off the coast of southern China each year. Lancelets' other economic use is as a laboratory study animal as they demonstrate the most primitive ‘vertebrate' characteristics that all aspiring zoology undergraduates need to know about in order to get that all important good grade.

Introduction to lampreys

There are 38 known species of lamprey in the world with recordings of further extinct species in the fossil record. They are found in both hemispheres of the globe, although they are confined to temperate rather than tropical regions. Three of these species can be found in the UK. These are the brook lamprey, river lamprey and sea lamprey. Lampreys are often called the jawless fishes for obvious reasons. They also lack scales. One British king, the youngest son of William the Conqueror no less, is believed to have died from eating a dodgy surfeit of sea lampreys. Supporters of King Harold were no doubt secretly celebrating on hearing the news. Interestingly, there remains a royal connection with lampreys to this day.

Brook lamprey life cycles

Brook Lamprey, copyright Paul Frear, Environment Agency

Parasitic lamprey life cycles

River lamprey, copyright Paul Frear, Environment Agency

Spread of lampreys

Sea lamprey, copyright Paul Frear, Environment Agency

UK distribution and conservation status

In contrast to the Great Lakes, all three UK lamprey species protected by law have become increasingly rare. Numbers throughout Europe have been on the decline for centuries, probably due to a combination of overfishing, migration blockage from weirs and dams and sedimentation of spawning habitat. For almost 200 years there have been insufficient availability of sea lampreys in the Severn Estuary for the City of Gloucester to be able to deliver a lamprey Xmas pie to the reigning monarch.

Lampreys in Canal & River Trust fisheries

The brook lamprey is very common on the Swansea Canal, where we recently successfully rescued many thousands by repeat electrofishing prior to carrying out dredging activity. Many are also present in the upper reaches of the Llangollen Canal. Much to our surprise, the Trust also recently rescued nearly 100 brook lampreys on the Gayton Brook culvert, which flows under the Trent & Mersey Canal near Stone. This example illustrates the need for undertaking fish rescues at locations which at first site might appear fishless, for it would have been an offence for the Trust or its contractors to have killed these lampreys.


The third group of primitive fishes are the hagfishes, which are also known as slime eels. These marine fish are prodigious producers of slime – a two foot long hagfish can produce two gallons of slime in under an hour. Despite this unattractive feature, hagfish form an important component in the diet of dolphins, seals and sea lions and hagfish overexploitation is having a knock on effect further up the food web. Broiled hagfish, known as anago-yaki, is a delicacy in Japan. Another commercial use of hagfish is their skin, which is the main source of eel skin wallets, purses and briefcases. Many hagfish are mud dwelling and don't require a lot of oxygen to keep going and the same applies to food. It's been calculated that one large carcass meal will keep a happy hagfish going for a whole year. Oh, I do wish I could somehow manage that.

Last Edited: 30 August 2016

photo of a location on the canals
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