The sea lamprey (Petromyzon marinus) is a parasitic lamprey native to the Northern Hemisphere. It is sometimes referred to as the "vampire fish".
Description
The sea lamprey has an eel-like body without paired fins. Its mouth is jawless, round and sucker-like, and as wide or wider than the head; sharp teeth are arranged in many concentric circular rows. There are seven branchial or gill-like openings behind the eye. Sea lampreys are olive or brown-yellow on the dorsal and lateral part of the body, with some black marblings, with lighter coloration on the belly. Adults can reach a length of up to and a body weight up to .
Etymology
The etymology of the genus name Petromyzon is from petro- "stone" and myzon "sucking"; marinus is Latin for "of the sea".
Distribution and habitat
The species is found in the northern and western Atlantic Ocean along the shores of Europe and North America, in the western Mediterranean Sea, the Black Sea, and as an invasive species in the shores of the Great Lakes. They have been found at depths up to 4000 meters and can tolerate temperatures of .
In North America, they are native to the Connecticut River basin in the United States. The largest European populations of sea lampreys are located throughout the southwestern areas of Europe (north-central Portugal, north-northwest of Spain, and west–southwest of France). These countries also support the main fisheries of the species.
Ecology
Sea lampreys are anadromous; from their lake or sea habitats, they migrate up rivers to spawn. Females deposit a large number of eggs in nests made by males in the substrate of streams with moderately strong current. Spawning is followed by the death of the adults. Larvae burrow in the sand and silt bottom in quiet water downstream from spawning areas and filter-feed on plankton and detritus.
After several years in freshwater habitats, the larvae undergo a metamorphosis that allows young, post-metamorphic lampreys to migrate to the sea or lakes, and start the adult hematophagous method of feeding. Some individuals start hematophagous feeding in the river before migrating to the sea, where sea lampreys prey on a wide variety of fish.
The lamprey uses its suction cup-like mouth to attach itself to the skin of a fish and rasps away tissue with its sharp, probing tongue and keratinized teeth. A fluid produced in the lamprey's mouth, called lamphredin, prevents the victim's blood from clotting. Victims typically die from excessive blood loss or infection. After one year of hematophagous feeding, lampreys return to the river to spawn and die, a year and a half after the completion of metamorphosis.
Lampreys are considered a delicacy in some parts of Europe, and are seasonally available in France, Spain, and Portugal. They are served pickled in Finland.
Physiology
Due to its lifecycle that switches between fresh and salt water, the sea lamprey is adapted to tolerate a wide range of salinities. Cell membranes on the surface of the gills are major contributors to ionoregulation. Changes in membrane composition influence the movement of different ions across the membrane, changing amounts of components to change the membranes' environment.
As the larvae (called ammocoetes) move towards the oceans, the ratio between saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA) in the gills shifts towards higher amounts of SFA, as they affect the fluidity of the membrane, and higher levels of SFA lead to a decrease in permeability compared to PUFA. Lamprey ammocoetes have a relatively narrow range of salinity tolerance, but become better able to withstand wider ranges of salinity concentrations as they reach later stages of life. Tight regulation of Na/K-ATPase and an overall decrease in expression of H-ATPase assists in regulating the lamprey's internal fluid and ion balance as it moves to areas of higher salinity.
Lampreys also maintain acid-base homeostasis. When introduced to higher levels of acids, they are able to excrete excess acids at higher rates than most other saltwater fishes, and in much shorter times, with the majority of the transfer of ions occurring at the gill surface.