Sea Lamprey

The sea lamprey has a complex life cycle which consists of four stages - egg, larvae, when they are filter feeders, juvenile, when they are parasitic and adult, when they spawn.

Adults

• Cylindrical
• Length: 305 to 610 millimeters
• Two dorsal fins, well separated
• Spade shape caudal fin
• Circumoral teeth on either side of opening, bicuspid
• Teeth in lateral rows of 5 to 7
• Breeding males develop prominent rope-like ridge on the back

Larvae

• Cylindrical
• 11 millimeters up to 200 millimeters - Upper size varies and is dependent on the temperature and food of stream environment
• Two dorsal fins, well separated

Eggs

• 0.8 to 1.3 millimeters in diameter
• Sticky

Juveniles

• 100 to 200 millimeters in length
• Newley transformed juveniles are grayish blue dorsally grading to white on the belly
• Two dorsal fins well separated

Adults

• Dark brown to black and marbled dorsally
• Light yellow to pale brown ventrally
• Yellow variants have marbled pattern similar to the darker variants

Larvae

• Brown dorsally and on sides, lighter ventrally
• Upper lip and suborbital region pigmented
• Branchial region above the branchial grove pigmented, except a light colored narrow band
• Caudal peduncle entirely pigmented

Juveniles

• Newly transformed juveniles are grayish blue dorsally grading to white on the belly

The semelparous adults, meaning that they breed and reproduce once in a lifetime, ascend Atlantic coast and Great Lake streams to spawn during early spring. During their 1980 research, P.J. Manion and L.H. Hanson documented this spawning in April. Earlier migrants are less sexually mature than those who arrive later to the spawning grounds. Prior to spawning, males develop a very pronounced median, rope-like ridge their back, as described by V.C. Applegate in 1950. 

Nest construction begins when the water temperature rise over 4.5º C, as documented by G.C. Becker in 1983. Males clear gravel, rubble and small stones from a circular area and deposit them in a crescent ring along the downstream margin of the clearing. Gravel, between 0.33 to 5.10 centimeters in diameter, along with a small amount of sand, is required for nest construction. Each stone is individually picked up and moved with the sea lamprey’s oral disk. Additionally, current must consistently flow in one direction over the nest. Female sea lampreys are known to assist in nest construction or construct nests later in the season, as documented by V.C. Applegate in 1950.

During the spawning act, a female will anchor firmly to the bottom of the nest by attaching to a large piece of gravel with her oral disk. The male uses his oral disk to attach to the dorsal side of the female, close to the head and gills. The male immediately wraps the posterior third of his body around the female so that their vents are approximated. Both individuals rapidly vibrate their bodies for two to five seconds to extrude their eggs and milt, after which the male releases the female. The eggs are carried by the current and lodge in the interstices of the nests downstream gravel rim. Intervals between spawning acts last about two to three minutes, 10 minutes and longer when they are close to being spent. Both the male and female add more stones to the downstream rim of the nest between each spawning act or between two to three spawning acts. Spawning can last from 16 hours to three and a half days, as documented by V.C. Applegate in 1950.

Once spawning is complete, one or both lamprey anchor to a rock near the upstream end of the nest and violently vibrated to dislodge sand from the bottom of the nest. The sand fills the space between the gravel, and adheres to and imbeds the eggs in place. Females drop away from the nests immediately after spawning and drift into pools where they die. Males can remain in the nest, curled into the deepest depression, for one to three days. Eventually, they also drop downstream when they lose strength and die.

Eggs are deposited into nests during the adult sea lamprey spawning act. Sea lamprey pro-larvae emerge from nests 11 to 31 days after spawning, as documented by V.C. Applegate in 1950, and later confirmed by Piavis in 1960 and later by P.J. Manion and A.L. McLain in 1971. They are carried downstream by the current and dive to soft stream substrate where they rapidly burrow by undulating in a figure eight motion with the posterior third of their body. Burrows are crescent or U-shaped and range from 1.3 to 5.2 centimeters in depth, as documented by V.C. Applegate in 1950. Larger larvae make deeper burrows. Preferred larval habitat consists primarily of silt with sand and detritus as secondary components. The sand fraction is mainly comprised of very fine, fine and medium sands. Coarse sands, gravel or rubble may also be present, but are a minor contribution. Surface cover is often provided by woody debris or aquatic macrophytes, as noted by the Great Lakes Fishery Commission in 2021. Over time, larvae drift downstream. Movement is related to temperature and high water levels. P.J. Manion and A.L. McLain reported in 1971 that most downstream movement occurred during floods during the months of March, April and May. Larger larvae tended to migrate to deeper water in substrate covered by course organic debris. 

Larvae develop in the substrate for about four to 17 years. P.J. Manion noted in 1967 that during this life stage, they filter feed on small particles like diatoms, and later in 1998, S.H. Bowman and others noticed that they also feed on detritus and bacteria from the water column which is immediately above the substrate. In 1980, J.W. Moore and J.M. Mallatt documented that to a lesser degree, they also sourced food from the sediment.

Larval sea lamprey then begin a dramatic metamorphosis where they develop eyes, an oral disk mouth covered in pointy, hooked teeth and a tongue covered with bony plates, that is also referred to as toothed. Fully metamorphosed lamprey are called juveniles. The juvenile migrate out of their natal stream and into the lake or ocean environment. Here, they attach to other fishes with their oral disk and teeth and feed on the blood of their host. This stage lasts for 12 to 18 months, and a single parasitic sea lamprey in the Great Lakes can destroy 19.3 kg of fish, noted W.D. Swink in 2003.

During the winter and early spring, juvenile sea lampreys stop feeding and begin to search for a suitable spawning stream. They enter stream, sexually mature into spawning adults and spawn during the spring and summer. Shortly after spawning both male and female fall off of the nest, drift downstream and die documented V.C. Applegate in 1950.

Sea lampreys spend 12 to 18 months in the parasitic stage, where they feed on other fish, as documented by V.C. Applegate in 1950. I.C. Potter and R.W. Hilliard documented in 1987 that sea lampreys attach to host fish with their oral suction disk and hooked teeth that embed in the flesh and maintain their position. The tongue is located in the center of the oral disk and has two sets of plates that form cutting edges, or teeth. The tongue moves in a piston motion and the plates rasp a hole in the side of the fish. Lamphredin, a lamprey anticoagulant, is secreted and has cytolytic effects on the integument, blood vessels and connective tissue of the host. However, Farmer and others in 1973, found that sea lampreys almost exclusively consume blood. W.D. Swink estimated in 2003 that single Great Lakes sea lamprey can destroy 19.3 kilograms of fish in its parasitic stage.

A sea lamprey can feed on any species of fish provided there is sufficient area for them to attach, as documented by H.A. Surface in 1898. In 1973, G.J. Farmer and F.W.H. Beamish concluded that the thermal distribution of host species in lakes and a fish’s relative size is important in determining lamprey predation.

In the Great Lakes, parasitic sea lamprey predate lake trout (salvelinus namaycush), burbot (Lota lota), rainbow trout (Salmo gairdneri), lake whitefish (Coregonus clupeaformis), lake herring (Coregonus artedii) and ciscoes (Coregonus spp.), as documented by G.J. Farmer in 1980, and lake sturgeon, as K.P. Holly and others noted in 2009. In the Atlantic Ocean, they are known to attack Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus harengus), haddock (Melanogrammus aeglefinus), pollock (Polachius virens), red hake (Urophycis chuss), sturgeons (Acipenser spp.), Atlantic mackerel (Scomber scombrus), swordfish (Xiphias gladius) and basking sharks (Cetorhinus maximus), as documented by H.B. Bigelow and W.C. Schroeder in 1948 and later by W.B. Scott and E.J. Crossman in 1973. In the Lake Cayuga Basin, brown bullhead (Ictalurus nebulosus), suckers (Catastomus spp.), carp (Cyprinus carpio), chain pickerel (Esox niger), northern pike (Esox lucius), walleye (Stizostedion vitreum vitreum) and longnose gar (Lepisosteus oseus) were some of the fish predated by sea lamprey, as documented by H.A. Surface in 1898.

Larval sea lamprey burrowed in the sediment are filter feeders. When feeding, their oral hood is positioned at or near the sediment surface, facing upstream. Water is pumped through the oral hood and expelled through the gill openings. Potential food items are drawn in via the larvae's unidirectional respiratory current, as documented by V.C. Applegate in 1950. Mucus produced serves to trap, aggregate and transport food particles, as documented by J. Mallatt in 1981. Food items include small particles like diatoms, documented by P.J. Manion in 1967, as well as detritus and bacteria, as documented by Bowen and others in 1998, from the water column immediately above the substrate. In 1980, J.W. Moore and J.M. Mallatt also noted that to a lesser degree, food comes from the sediment as well.

Larval sea lamprey develop in streams. Preferred habitat consists primarily of silt with sand and detritus as secondary components. The sand fraction is mainly comprised of very fine, fine and medium sands. Coarse sands, gravel or rubble may be present, but their contribution is minor. Surface cover is often provided by woody debris or aquatic macrophytes, as noted by the Great Lakes Fishery Commission in 2021. Parasitic sea lamprey are attached to, and feed on, fish in lake and ocean environments, as documented by C.O. Brant in 2019.