Lamprey - biology.

Lamprey - biology. Lamprey, common name for any of about 40 species of eel-like, jawless fishes. Lampreys are widely distributed in freshwater streams and seas of temperate and subarctic regions throughout the world, except for the waters off southern Africa. In the Middle Ages lampreys were a delicacy, but they are now used mainly for bait. Lampreys are smooth-skinned, and they attain a length of about 91 cm (about 36 in). Adult forms of parasitic species live on the blood of fishes and sometimes cause serious depredations in fisheries. Like the related hagfish, their mouths are circular, without jaws, and equipped with a pistonlike tongue that creates suction when the mouth is placed against an object and the tongue is drawn back. The inner margin of the mouth and the edges of the tongue are equipped with numerous small, horny teeth with which the lamprey pierces the flesh of fishes. The adult forms of nonparasitic lampreys do not eat, spawning and dying soon after their metamorphosis into the mature form. On each side of the body is a row of seven respiratory openings through which the lamprey breathes. The animal has no bony skeleton whatsoever, its chief support being derived from the cartilaginous notochord. The sea lamprey is a marine species, native to the Atlantic coast of North America and Europe. In various areas it has become landlocked and has thus adapted to a life cycle spent entirely in fresh water. Long known in Lake Ontario, the sea lamprey invaded Lake Erie in the 1920s, where the relative warmth of the water inhibited its reproduction. The species migrated to Lake Huron in 1939 and then to Lake Michigan. Within a few years the animal had severely damaged the valuable trout fisheries in these lakes by competing with the fishing industry for the available trout. Subsequently invading Lake Superior, the lamprey soon became a serious threat to the fishing industry there. In September 1954, the United States and Canada signed an agreement for joint action against the lamprey. The most effective methods of control have proved to be the electromechanical weir, which electrocutes the adult lampreys as they head upstream to spawn, and the use of selective chemicals to kill the larvae living in the stream bottom. All lampreys breed in fresh water, usually in clear streams with gravelly, sandy bottoms. Marine lampreys ascend freshwater streams like salmon, passing rapids that obstruct their path. Unlike salmon, they occasionally attach themselves to rocks by their sucking mouths in order to rest or as an aid in moving through swift currents. Males and females move stones with their mouths and excavate a shallow nest in which the female deposits about 62,500 eggs. As the eggs are laid, the female stirs up the sand on the bottom of the stream so it rises and adheres to the eggs, weighing them down. After the spawning, which occurs once in the lifetime of a lamprey, the adult fish wastes away, and dies in two to three months. The eggs hatch in two to three weeks, and the larvae drift downstream until they settle in a quiet pool, where they burrow in the mud. The larvae are completely unlike the adult; they are blind and toothless, and have a different feeding mechanism. A fringe of tiny barbs called barbules surround the mouth, serving as a strainer to capture the small forms of life on which it lives. The larva is so unlike the adult that scientists formerly believed it to be a member of a special genus, and the name ammocoete is still applied to it. The ammocoete remains in the mud for at least four years, at the end of which time it undergoes a metamorphosis into the adult form and departs for its adult habitat. Scientific classification: Lampreys make up the lamprey family, Petromyzontidae, of the order Petromyzontiformes. The sea lamprey is classified as Petromyzon marinus. The larva referred to as the ammocoete had previously been classified in the genus Ammocoetes. Contributed By: Kenneth A. Chambers Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.