Sea lamprey

Petromyzon marinus

Family - Petromyzontidae

sealamprey.jpg (36133 bytes)

 

Lamprey

Steve Smith

The lamprey are a group of jawless fishes in the family Petromyzontidae. They are eel-like fishes that lack scales, jaws, paired fins, and bone. Lampreys are found in both fresh water and marine environments in North America, South America, Europe, Asia, and Australia. There are 38 known species, 19 of which are found in fresh water. All of the lampreys have an interesting life cycle that includes a larval phase and adult phase that is parasitic in some species (Page and Burr 1991).

Lampreys are elongated and cylindrical in shape with the adult form having a round oral disc at the anterior end, and flat rounded posterior end. They have dorsal fins on the posterior half of the body, but have no pelvic or anal fins. Adults have dark colored backs varying by species from a dark gray to brown with a lighter underbelly. They range in size from the small Northern Brook Lamprey at about 15 centimeters to the larger Sea Lamprey that can reach 61 centimeters. Species are identified by the pattern of the teeth on the oral disc.

One of the most interesting aspects of the lamprey is their life cycle. Adult lampreys spawn in riffle areas of rivers, streams, and brooks. By using their suction cup -like discs they make spawning pits by moving around stones in the stream bed. Eggs are laid and fertilized in these pits. Eggs hatch into a fresh water larval stage. At this phase, called ammocoetes, the lampreys are without eyes and have an oral hood that is to become the oral disc. Lampreys remain ammocoetes for a period of several years. After hatching in the riffle the ammocoetes are pulled downstream by the current. When they reach an area of preferred habitat they did down into the silt or sand that is on the stream bed. The ammocoetes position themselves so that the oral hood is extending into the flowing stream so that they can filter out the microorganisms on which they feed (Hardisty and Potter 1971). The ammocoetes will remain concealed in the substrate for a period of three to eight years before beginning metamorphosis into adulthood. The ammocoetes will leave their burrows occasionally, but never for extended periods of time because they are not very strong swimmers.

The lampreys can be regarded as a "highly successful" group of animals by many standards of assessment, long periods of survival in geological time, their present distribution, or simply biomass in a given stream or river. This is most likely due to the fresh water phase when the ammocoetes are burrowed in the substrate (Hardisty and Potter 1971). During this period of years the ammocoetes suffer from very little predation, and their growth and development is not dependent on availability of nutrients, but rather on the mechanics of microphagous feeding (Hardisty and Potter 1971).

After the rather long period spend in the larval phase the lampreys "transform" into the adult phase. The transformation lasts for about four to five weeks. During this time the ammocoete develops an oral disc for feeding, and undergoes extension of the body, modification of the gill openings, eruption of the eyes, development of teeth, and changes in pigmentation (Hardisty and Potter 1971). It is now believed by some that thyroid hormone activity, as well as environmental cues triggers the metamorphosis of ammocoetes into adults (Youson 1997). Once this development is complete the lamprey begin their migration out of the river or stream back to the ocean, or in some cases lake, in which the adult form lives. Of the 38 known species only about 9 or 10 pass through a parasitic marine phase. All of the remaining species spend their entire life in fresh water, and only about five of these are parasitic. The remaining nonparasitic species are called brook lampreys that do not feed after transformation (Hardisty and Potter 1971). The parasitic adult lampreys prey on fishes in the ocean or in lake systems by attaching to the fish with their toothed oral suction like disc and breaking the skin and using a tongue that is covered with keratinized teeth to suction off blood and bits of tissue (Britannica Online). The landlocked sea lamprey, which is common in the Great Lakes as well as in Lake Champlain, prefers to prey on salmonoid fishes, salmon and lake trout in particular. In the one year parasitic phase, the landlocked Atlantic sea lamprey is capable of sucking the life out of up to forty pounds of fish (Bower 1998). The nonparasitic species do not feed after transformation; they simply reproduce and then die.

Lampreys move and breath much like most other fishes, by swimming when they have to, and breathing through gills. Parasitic adults are usually attached to a mobile fish so they do not need to swim often, but when they become separated they swim to find another host by undulations of the body (Britannica Online). Ammocoetes are not strong swimmers but they can move in the same manner when necessary. The ammocoetes respiration consists of a unidirectional flow of water over the gills. Water enters through the mouth, passes over the gills then leaves through seven pairs of gill clefts. The adult has similar gill structure, but the water flow changes unidirectional to tidal. Water moves in and out through gill openings. Water enters into gill pouches where it flows over the gills and the branchial constrictor muscles contract and push water out of the gill pouches (Hardisty and Potter 1971).

The lampreys are most closely related to another group of jawless fishes called hagfishes. The hagfishes are totally marine - living in deep water with a muddy bottom. They feed similarly to lampreys, but on a variety of hosts, invertebrates and dead fishes (Britannica Online). The hagfishes, unlike lamprey, do not go through a larval phase, they hatch from an egg and develop directly into a miniature adult.

The lampreys most likely evolved from an anaspid or an anaspid like stock, and they are found in fossil records dating to the Pennsylvanian period. The lampreys along with the hagfishes are the only remaining representatives of the most primitive vertebrates, the fish lacking jaws (Hardisty and Potter 1971).

Locally the most abundant species of lamprey are the landlocked Atlantic sea lamprey (Petromyzon marinus) and the silver lamprey (Ichthyomyzon unicuspis). The landlocked sea lamprey is the most important at this time because it is believed to be a non-native nuisance species that was introduced into the lake via the Champlain Canal. The adults spawn in upstream sections of many rivers, brooks, and streams along both New York and Vermont shores. It has become a problem because of its effects on sport fish populations such as landlocked Atlantic salmon and lake trout. Lamprey control efforts in Lake Champlain began in the early 1990s to try to decrease sea lamprey populations. These measures include treating spawning streams and deltas with chemicals to kill adult or larval lampreys. The use of traps and control structures such as dams blocking the upstream migration have also been implemented (Lake Champlain Basin Program 1999).

The lampreys are a group of quite unique fishes that have lived in the world's waters for a very long time. It has been only in the last decade or so that many of us have learned anything substantial about lampreys, mainly because of their recognition, in the sea lampreys case, as a nuisance. I believe there will be much more learned about the lampreys as more and more attention is paid to them for a variety of reasons, mainly their effects on the sport fish population which has recreational and, in some cases, economic effects on the population in this region.

 

Literature Cited

Bower, J., April 1998. The persistent parasite. Audubon. New York 100:16-18

Britannica Online. Vertebrate Natural History, The cyclostomes. Available:

http://www.eb.com:180/bol/topic?eu=119319&sctn=1.

Britannica Online. Lamprey. Available: http://www.eb.com:180/bol/topic?eu=4807&sctn=1.

Cadmus, Laura. 1998. June 10 - last updated. Lake Champlain Basin Program. Online. Available: http://www.anr.state.vt.us/champ/nuissum.htm#lamprey.

Hardisty, M. W. and I. E. Potter. 1971. The Biology of Lampreys, Volume 1. Academic Press, London, New York. Pp. 1-200.

Hardisty, M. W. and I. C. Potter. 1971. The Biology of Lampreys, Volume 2. Academic Press, London, New York. Pp. 287-300.

Page, Lawrence M., Burr, Brooks M. 1991. Freshwater Fishes. Houghton Mifflin Company, Boston, New York. Pp. 14-24.

Youson, John H., December 1997. Is lamprey metamorphosis regulated by thyroid hormones? American Zoologist. Chicago. 37:441-460.