Lampetra fluviatilis (Linnaeus, 1758)

Taxon Information

• Geographical Distribution: The river lamprey occurs over most of western Europe, in seas and accessible rivers from southern Norway to the western Mediterranean and includes several purely freshwater populations. It is indigenous to the British Isles where it can be found in most of the accessible river systems south of the Great Glen, Scotland. The only purely freshwater population in Britain can be found in Scotland in the Loch Lomond catchment area and is a dwarf form.
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• Size Range: Adults may attain a maximum length of around 50cm, weighing 150g but 30-35cm is the average length. Adult females 32-34cm long usually have a mean weight of approximately 62g. The dwarf form and the Loch Lomond (Scotland) race are smaller and average 18-24cm.
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• Life Cycle Summary: Adult lampreys normally enter fresh water from estuaries in the late summer and autumn of the year prior to spawning and migrate upstream during the night only. Spawning (in pairs or groups) starts when the water temperature reaches 10-11˚C in stony or gravel-rich stretches of running water. Shallow depressions are created in the river bed by up to a dozen or more adults lifting away small stones with their suckers. Each female can lay between 19,000 and 20,000 clear eggs (approximately 1mm in diameter) in these nests. All adults die after spawning. Ammocoete larvae hatch in April-May after an incubation period of 15-20 days (dependent on temperature) and either swim, or are carried downstream by currents to silty sandbeds into which they burrow and filter-feed organic material for 3-5 years. After several years of larval development the metamorphosis into adult happens in just a few weeks during July-September. Adult lampreys then migrate to the sea or to a large lake during darkness and attach themselves to the skin of fish essentially becoming parasitic. The adult stage lasts 12-18 months. Feeding ceases and adults detach themselves in the autumn. The transition into fresh water usually occurs from October - December and it is thought that an increase in fresh water discharge is the main environmental factor responsible for initiating the movement from sea to estuary, although temperature may be a contributing factor. Migration only happens during the night with arrival at the spawning grounds occurring April-May.
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• Life Stage: Ammocoete (larval stage)
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• Free Living Environment: Burrow into silt/sandy beds in quiet waters as filter feeders of organic material.
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• Reproduction Capacity: Sexually immature.
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• Transmission In: After incubation of 15-30 days (depending on water temperature) the larvae hatch and drift downstream from the spawning area.
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• Host: 3-5 years.
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• Morphology: Dull grey-brown colour, lighter underneath and usually indistinguishable from the ammocoetes of brook lampreys (Lampetra planeri). Usually 9-12cm at the end of this stage, weigh less than 2g and are blind.
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• Transmission Out: Swim/drift downstream.
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• Life Stage: Macrophthalmia (juvenile stage)
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• Free Living Environment: Downstream rivers and estuaries.
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• Reproduction Capacity: Sexually immature.
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• Duration: Several weeks.
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• Morphology: 12-30cm long with the silvery colouring of the adult feeding stage.
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• Life Stage: Adult (feeding)
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• Reproduction Capacity: Sexually immature.
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• Host: Definitive Host: Any estuarine fish species but particularly herring (Clupea harengus), sprat (Sprattus sprattus) and flounder (Platichthys flesus) or, in the case of the dwarf Loch Lomond population, powan (Coregonus lavaretus)
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• Site Within Host: Ectoparasitic on the skin of the host.
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• Duration: 12-18 months
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• Morphology: Average adult length is approximately 30cm although individuals up to 50cm can be found and the dwarf population in Loch Lomond can be less than 20cm. The feeding phase is silvery with no scales and can appear bloated.
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• Pathology: Can be fatal especially if the host body cavity is penetrated or more than one lamprey parasitise an individual.
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• Transmission Out: Detaches from fish host to migrate upstream to spawning grounds.
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• Stage Note: Host Habitat: Freshwater rivers and lakes, estuaries, coastal areas
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• Ecological and Habitat Requirements: The river lamprey is not confined to freshwater habitats, and can also be found in marine and brackish habitats. Adults require adequate stretches of gravel and small stones in flowing water for spawning and beds of sandy silt in quieter waters for the larvae are needed.
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• Current Status: It is listed as a Lower Risk Near Threatened species on the 2006 IUCN Red List of Threatened Species and is a proposed UK Biodiversity Action Plan priority species. It is listed as a protected species in Appendix III of the Bern Convention for the Conservation of European Wildlife and Natural Habitats and in Annexes IIa (conservation requiring Special Areas of Conservation) and Va (taking in the wild and exploitation may be subject to management measures) of the EU Habitats and Species Directive.
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• Physiology: The physiology of the river lamprey is complex as it is an anadromous species and so must be able to cope with changes in salinity. The larval lamprey (or ammocoete), lives concealed in silt deposits of rivers and streams and is stenohaline (cannot tolerate fluctuations in salinity). The ammocoete osmoregulates in a manner similar to freshwater teleosts by balancing the large osmotic influx of water with copious urine production. Any salt lost due to excretion or diffusion is thought to be replaced by an active uptake mechanism located in the epithelium of the gills. After 3-5 years the ammocoete undergoes a metamorphosis into a macrophthalmia - the sexually immature, non-feeding life stage. The macrophthalmia migrates to areas with stonier substrate and is euryhaline. In the ocean, the lamprey is subjected to continual osmotic water loss and influx of ions which it regulates by actively expelling ions across the gill epithelium and via the kidneys. As a result of its change in function from ion-uptake only in the ammocoete to ion-uptake or ion-secretion in the macrophthalmia, the ultrastructure of the epithelium of the gill can be found to have two cell types (as opposed to only one in the ammocoete). This metamorphosis also involves the transformation of the endostyle, which produces the mucus secretion responsible for trapping food particles in the pharynx of the ammocoete, into the thyroid gland of the macrophthalmia. The adult lamprey, after parasitising fish in the sea or estuary for up to 18 months, undergoes further physiological changes characterised by a prolonged period of starvation. During this time the gonads develop at the expense of other body tissues such as the intestine, which degenerates to just a thin thread of tissue. During the initial period of migration upstream to spawn, the lamprey exhibits a limited degree of euryhalinity, as it reorganises its osmoregulatory system once again to better reflect the gill cell structure of the ammocoete with smaller ion-uptake cells replacing the larger ion-excretory cells. At sexual maturity the body tissues show signs of severe deterioration as the energy stores procured during the feeding stage are exhausted. Although there are major changes in gill tissues, it is not clear whether this is due to degeneration, changes in ion-balance or pheromones involved in spawning. One distinct dimorphic characteristic however, is that male lamprey gills contain abundant sudanophilic cells similar in structure to ion-transporting cells, whereas female lamprey gills do not.
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• Food and Feeding: As larvae, river lampreys filter organic material but as adults they become parasitic on fish, feeding on blood and tissues of the host.
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• Threats: Threats to the river lamprey include water abstraction and land drainage leading to unsuitable habitats, eutrophication smothering and creating anoxic conditions in spawning and larval areas, and obstacles such as weirs and dams on migration routes preventing them from reaching spawning areas. Unusually, special attention must be paid to silt beds, as a significant proportion of the lamprey life cycle occurs here and fishery management aimed at improving conditions for other fish and wildlife may adversely affect these areas (e.g. improving conditions for salmonids includes dredging ammocoete silts).
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• Economic Value: The river lamprey is an important commercial species in Scandinavia where the adults are caught as they migrate upstream. Since they are cartilaginous fish with no bones, and the gut is empty during migration, they are grilled or smoked and eaten whole. Although they are of no angling value, a commercial fishery on the Yorkshire Ouse takes approximately two tonnes of river lamprey annually for use as bait.
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