Sea lamprey

Physical Description and Life Cycle

The sea lamprey has a distinctive, eel-like body that lacks paired fins, with a round, sucker-like mouth filled with concentric rows of sharp teeth. Its mouth is as wide as or wider than its head and contains a rasping tongue. The body is typically olive or brown-yellow on the back and sides with black marbling, and lighter on the belly. Behind each eye are seven distinctive gill openings. Adults can grow up to 120 centimetres long and weigh up to 2.3 kilograms over a lifespan of approximately seven years.

Sea lampreys are anadromous, meaning they migrate from saltwater or lake habitats into freshwater rivers to spawn. Males build nests in the gravel substrate of streams, where females deposit a large number of eggs. After spawning, the adult lampreys die. The larvae, called ammocoetes, hatch and burrow into sandy or silty stream bottoms where they live for several years, filter-feeding on plankton and detritus.

Following a metamorphosis, the young lampreys develop their parasitic mouthparts and migrate to the sea or lakes to begin feeding. They attach to fish using their suction-cup mouth, rasp through skin and tissue with their tongue and teeth, and feed on the host's blood and bodily fluids. A substance in their saliva called lamphredin prevents the host's blood from clotting. After a 12 to 18 month parasitic feeding phase, they return to freshwater rivers to spawn and complete their life cycle.

Invasion of the Great Lakes

The sea lamprey is a native species of the Atlantic Ocean but became a catastrophic invader in the Great Lakes. It is believed to have first entered Lake Ontario in the 1830s, possibly via the Erie Canal which opened in 1825. For decades, Niagara Falls acted as a natural barrier preventing further spread. This changed with the construction and subsequent modifications of the Welland Canal, which allowed lampreys to bypass the falls.

The invasion proceeded rapidly through the upper Great Lakes. Sea lampreys were first found in Lake Erie in 1921, Lake Michigan in 1936, Lake Huron in 1937, and Lake Superior by 1938. In these new environments, native fish species like lake trout, lake whitefish, chub, and lake herring had no evolutionary defences against the aggressive parasite. Each individual sea lamprey can kill up to 18 kilograms (40 pounds) of fish during its feeding period.

The impact was devastating. Lamprey predation, combined with historical overfishing, caused the collapse of commercially and ecologically vital fish stocks, particularly lake trout. The elimination of these apex predators allowed another invasive species, the alewife, to explode in population, further destabilizing the Great Lakes ecosystem. The invasion inflicted significant economic damage on fisheries and altered the ecological balance of the world's largest freshwater system.

Control and Management Programs

The control of sea lampreys in the Great Lakes is a coordinated, binational effort under the Great Lakes Fishery Commission, established by a convention between Canada and the United States. The operational partners are Fisheries and Oceans Canada and the United States Fish and Wildlife Service. This program is considered the only successful large-scale aquatic vertebrate pest control program in the world, having reduced sea lamprey populations by approximately 90 percent in most areas of the Great Lakes. The control program uses an integrated pest management approach, combining several methods to attack the lamprey at different life stages.

The primary tool is the application of lampricides, selective pesticides that target larval sea lampreys in their nursery streams. The most commonly used lampricide is TFM (3-trifluoromethyl-4-nitrophenol), which disrupts the energy metabolism of lamprey larvae. Another compound, Bayluscide, is often used in combination with TFM or in a granular form for slow-moving waters. As of 2018, no resistance to these lampricides had been detected in Great Lakes populations. Water samples are collected before, during and after each application to monitor effectiveness and environmental impact.

Other control methods include the use of barriers placed in streams to block the upstream migration of spawning adults. Modern barrier designs aim to impede lampreys while allowing passage for other fish species. Furthermore, ongoing research explores the use of pheromones to manipulate lamprey behaviour, such as luring them into traps or away from spawning grounds. Control efforts are continuous, with the Sea Lamprey Control Centre launching its field season annually, as seen in the 2026 season. About 200 Great Lakes tributaries and larval hotspots are regularly treated with lampricides.

Recent Management and Local Incursions

Sea lamprey control is an ongoing annual activity across the Great Lakes basin. For example, in the 2025 control season, a total of 2,977 invasive sea lampreys were captured as part of the control program. The 2026 control season began in April, with crews from Fisheries and Oceans Canada applying regulated lampricides to streams and still-water areas across the region between April and November. These proactive measures are essential for maintaining a healthy balance in the ecosystem and protecting native fish populations.

New local infestations continue to be discovered and treated. Larval populations were detected in sections of the Rouge River watershed within Rouge National Urban Park in Ontario. In response, trained staff from Fisheries and Oceans Canada treated affected river sections with lampricide in late April and early May of 2024. During such treatments, water quality is closely monitored, and the lampricide, which poses minimal risk to humans and most aquatic life, dissipates naturally. Affected streams and tributaries are typically treated every three to five years as part of the ongoing control cycle.

Visitors may notice a temporary orange-red or yellowish-green discolouration of the water during lampricide treatments, which typically clears within 12 hours. As a precaution, authorities advise avoiding unnecessary exposure to the water during these treatment periods. The Great Lakes Fishery Commission coordinates the sea lamprey control program across the basin. This program involves applying lampricides like TFM and Bayluscide to streams and still-water areas. Control efforts are carried out by agents of Fisheries and Oceans Canada and the United States Fish and Wildlife Service. These proactive measures help protect native fish populations by targeting sea lamprey larvae with minimal harm to other aquatic life.

Physiology and Adaptations

The sea lamprey possesses remarkable physiological adaptations for its dual life in salt and fresh water. Its gills are central to ionoregulation, maintaining internal salt balance. As larvae metamorphose and prepare for migration to the sea, the fatty acid composition in their gill membranes changes to reduce permeability and better handle higher salinity. Key enzymes like Na+/K+-ATPase are tightly regulated to manage this transition, and lampreys become more tolerant of salinity changes as they mature.

As a parasite that feeds on blood, the sea lamprey has evolved a high tolerance for urea, a nitrogenous waste product that is toxic to most fish in high concentrations. This allows it to parasitize elasmobranchs like sharks and rays, which have high urea levels in their blood. The lamprey can excrete urea at extremely high rates. Compounds like trimethylamine oxide from the blood of these hosts help counteract urea's detrimental effects, enabling the lamprey to feed on a wide variety of fish.

The sea lamprey maintains acid-base homeostasis effectively. When introduced to higher levels of acids, it can excrete excess acids at higher rates than most other saltwater fishes, and in much shorter times. The majority of this ion transfer occurs at the gill surface. The sea lamprey is also adapted to tolerate a wide range of salinities due to its lifecycle that switches between fresh and salt water. Furthermore, it can tolerate high concentrations of urea obtained from the blood of prey like sharks and rays. These physiological adaptations contribute to its success as a parasitic organism in diverse environments.

Genetics and Scientific Research

The genome of the sea lamprey was fully sequenced in 2013, revealing unusual characteristics compared to other vertebrates. It has a distinctive guanine-cytosine content and amino acid usage patterns. The genome is highly repetitive, with about 35 percent composed of repetitive elements, and it undergoes a drastic rearrangement during early embryogenesis where roughly 20 percent of germline DNA is shed from somatic tissues. Northern lamprey species hold the record for the highest number of chromosomes among vertebrates, ranging from 164 to 174.

The genome of Petromyzon marinus was sequenced in 2013. The lamprey genome may serve as a model for developmental biology and evolution studies involving transposition of repetitive sequences. The genome undergoes drastic rearrangements during early embryogenesis and is highly repetitive. Two genes important to immune function, CDA1 and CDA2, were first discovered in P. marinus and are conserved across lampreys. Scientists trying to eliminate the Great Lakes problem are coordinating with genetic scientists, hoping to find out more about its immune system from this research.

Scientific investigation continues to support control efforts beyond genetics. Other scientists study lamprey pheromones to develop behavioural control methods. Research into newly synthesized pheromones aims to understand how migratory and sex pheromones lure adults to spawning streams, with the goal of using these compounds in targeted, environmentally friendly control strategies. The Great Lakes Fishery Commission regularly accepts pre-proposals for its Sea Lamprey Research Program to fund such innovative work, as seen with deadlines in January and July 2026.

Human Interaction and Uses

In its native European range, the sea lamprey is harvested as a food fish and is considered a delicacy in several countries. The largest European populations and main fisheries are located in southwestern Europe, particularly in Portugal, Spain, and western France. The fish is prepared in various ways, often cooked or grilled, and is also served pickled in countries like Finland. It is occasionally caught in the rivers of Latvia alongside river lampreys, reflecting its cultural and culinary significance in those regions.

In stark contrast, within the Great Lakes basin, the sea lamprey is viewed exclusively as a destructive pest and a threat to a multi-billion dollar fishery and ecosystem. Millions of dollars are spent annually on its control. The Great Lakes Fishery Commission coordinates not only control operations but also a dedicated sea lamprey research program, with pre-proposals for research funding accepted on an annual basis, as seen with deadlines in January and July 2026. This represents a major ongoing investment in protecting the lakes from this invader.

In North America, sea lampreys are native to the Connecticut River basin in the United States. The Connecticut Department of Energy and Environmental Protection has introduced sea lampreys to freshwater rivers and lakes of the Connecticut River watershed. They have also worked to provide easier access around dams and other barriers for the lampreys to reach spawning sites high upstream. After migrating up the rivers to spawn, the adult lampreys quickly die of natural causes and decompose. This decomposition provides a food source for the native freshwater fish species.

Questions about Sea lamprey

How did the sea lamprey get into the Great Lakes?

The sea lamprey is native to the Atlantic Ocean. It was likely introduced to the Great Lakes region through the Erie Canal in 1825 and the Welland Canal in 1919. It was first contained to Lake Ontario by the natural barrier of Niagara Falls. After the Welland Canal was built, sea lampreys bypassed the falls and invaded the remaining Great Lakes: Lakes Erie by 1921, Michigan by 1936, Huron by 1937, and Superior by 1938.

Why is the sea lamprey a problem in Canada?

The sea lamprey is a devastating invasive parasite in the Great Lakes, a vital Canadian ecosystem. It attacks and kills native fish like lake trout, lake whitefish, and herring, with each lamprey capable of killing up to 18 kilograms of fish. Its predation contributed to the collapse of commercial fisheries and disrupted the ecological balance of the lakes. Controlling it requires an ongoing, costly binational effort to protect the fishery and restore native species, making it a significant environmental and economic problem.

What is being done to control sea lampreys in the Great Lakes?

Control is managed by the Great Lakes Fishery Commission, a Canada, U.S. body, with operations carried out by Fisheries and Oceans Canada and the U.S. Fish and Wildlife Service. The primary method is applying lampricides like TFM and Bayluscide to streams to kill larvae before they become parasitic. Other methods include using barriers to block spawning migration and researching pheromones for behavioural control. This integrated program has reduced sea lamprey populations by about 90 percent in most areas. The control season runs annually, with treatments applied to hundreds of tributaries.

Are lampricides used for control safe for other wildlife and people?

Yes, the lampricides used, primarily TFM and Bayluscide, are applied at concentrations specifically designed to target sea lamprey larvae while posing minimal risk to other aquatic organisms, pets, and humans. The compounds disrupt a metabolic pathway that is more critical to lampreys than to most other fish. Water quality is closely monitored before, during, and after application. The lampricides dissipate naturally, and any temporary water discolouration typically clears within hours. Visitors are simply advised to avoid unnecessary water contact during treatment periods as a standard precaution.

What does a sea lamprey look like?

The sea lamprey has a smooth, eel-like body without paired fins. Its most distinctive feature is its round, jawless, sucker-like mouth, which is as wide as its head and lined with concentric circles of sharp teeth surrounding a rasping tongue. It has seven round gill openings behind each eye. Its colour is usually olive or brown-yellow on the back and sides with dark marbling, and lighter on the belly. Adults can grow quite large, reaching up to 120 centimetres in length.

Are sea lampreys ever eaten by people?

Yes, but not in the Great Lakes region where they are considered a pest. In parts of their native European range, particularly in Portugal, Spain, and France, sea lampreys are harvested and are considered a delicacy. They are prepared in various ways, often cooked or grilled, and are also served pickled in countries like Finland. In these cultures, lamprey fisheries are a seasonal tradition. In North America, they are not consumed and are targeted solely for control and eradication in invaded ecosystems.

Sources: Wikipedia and current public reporting, checked by the Your Space Hamilton desk. Last updated 2026-10-21.