(full classification can be found below)
The sea lamprey is a relatively primitive, eel-like fish that feeds by attaching itself to and sucking the blood and other bodily fluids from larger fish. The sea lamprey is also known as the common lamprey, great sea lamprey, lake lamprey, lamprey eel, and plain old lamprey. Sea lampreys are native to the Atlantic Ocean (and the streams and rivers it connects to during certain times of the creatures' lives) but canals made by humans over the years have enabled them to gain access to the Great Lakes, where they are now a common find and have caused a large amount of damage to the local fish population since they were noticed there in 1921. Originally, the sea lamprey spent most of its adult life in the salt water ocean, migrating upstream into fresh water for breeding but because the species has been able to gain access so far inland many sea lampreys now live exclusively in fresh water.
The sea lamprey begins its life in a form during which it's referred to as an ammocoete. After developing in an egg for about 13 days, the 6.4 millimetre ammocoete emerges without functioning eyes or teeth with a fleshy hood hanging over its mouth. Hatching occurs in April or May. Recently hatched ammocoetes are swept downstream and enter their 'sedentary phase.' The ammocoete burrow tail-first into soft sand, mud, and other sediments. Once in its burrow, the ammocoete will curve its lower body so that the creature is in an L-shape. At this point the ammocoete will filter feed on microorganisms passing by it in the stream's current. Ammocoetes won't burrow in areas where the water flow is greater than 0.8 metres per second and once burrowed will seldom leave (though they will change their positioning frequently). Ammocoete burrow depth can range from only a few to 30 centimetres. The two primary reasons an ammocoete might leave its burrow before its sedentary phase is complete are low oxygen levels and high carbon dioxide levels. The sedentary phase of the sea lamprey's life can last as short as 3 or as long as 17 years.
Eventually the ammocoete undergoes a metamorphosis and becomes a free-swimming juvenile sea lamprey. This transformation usually begins in mid-July and may last until September of the same year. During this time, the sea lamprey develops functioning eyes, a large number of teeth and its tongue within its sucking disc (the creature has no actual jawbone), and the hood over its mouth goes away. The creature changes its colour from a dull brown to blue-grey on its dorsal side and silver-white on its ventral side. The juvenile sea lamprey is about as wide as a pencil and 13 to 15 centimetres in length. At this point, the sea lamprey ceases to filter feed and begins to live off of the blood of other fish.
The sea lamprey has no fins, achieving movement by moving its entire body back and forth. The wave it moves its body in increases in speed slightly as it nears the tail-end of the creature and may be completed in as short as 100 milliseconds or as long as 4 seconds, depending on the speed the lamprey wants to move at. The faster the sea lamprey waves its body like this, the faster it can move. The sea lamprey steers by bending its body in the direction it desires to turn. Sea lampreys can move very quickly in short bursts but must usually rest afterwards, which they do by attaching themselves (with their sucking discs) to rocks and waiting.
The now-free-swimming sea lamprey will remain in the fresh water streams for a few months (the lampreys so far inland that they never venture into the Atlantic will remain in streams and lakes their entire lives). Sea lampreys begin journeying to the Atlantic in late October and may arrive there as late as May. The sea lamprey's adult life typically ranges from 12 to 20 months. As adults in the ocean, sea lampreys can grow to be up to 120cm (mature landlocked sea lampreys typically range from 30.5 to 61.0cm). During this time the lampreys feed by finding a host (either through eyesight or a well-developed sense of smell) and attaching to the host creature with their suction disc. Prior to attaching, the sea lamprey will raise its head and open the disc. Once the disc touches the skin of its host, it need not attach right away, giving the lamprey the option of exploring the surface of the host to find a more favoured position. Once a satisfactory position is found, the lamprey brings its teeth into contact with the host and holds on tightly.
An anticoagulant in the sea lamprey's saliva will keep the wound it inflicts open for a few hours or a few weeks. The length of time the sea lamprey spends sucking blood and other fluids from its hosts can vary greatly, depending on the time of year, the size of the victim, and where the lamprey is attached. The average feeding time of adult sea lampreys in a laboratory is 76 hours. Juveniles in the lab have fed up to 220 hours. The feeding of the sea lamprey will likely kill smaller fish, though larger fish have been caught bearing lamprey wounds but no longer any lampreys themselves. Though the sea lamprey apparently prefers splake, carp, sucker, bullhead, rainbow trout, and bass to other types of fish, it will apparently attach itself to any type of fish and even whales if necessary. Scientists have estimated that a single sea lamprey will kill an average of 18.5 pounds of fish throughout its parasitic phase. In order to grow from its juvenile stage to sexual maturity, a single sea lamprey must ingest up to 3 pounds of blood. It is for these reasons that the sea lampreys living within the Great Lakes are such a threat to the native fish, as within the Great Lakes the fish's only predator are humans.
Near the end of the sea lamprey's life, it will migrate upstream to breed and shortly thereafter die (sea lampreys are anadromous, as are trout and a number of other fish). Sea lampreys begin their upstream migration in April and may continue as late as July. Once far enough upstream, male sea lampreys begin creating nests in gravel. The horseshoe-shaped nests are typically between 30-64cm deep and form a ridge that's 0.9-5.2cm in diametre. The water velocity over the nest is usually between 0.5 and 1.5 m/s in one direction and the temperature between 15.6 and 21.2 degrees celcius (18 degrees celcius is the optimum temperature). To mate the female sea lamprey anchors herself with her suction disc to a rock near the nest and the male wraps himself around her, bringing their genital pores together. Every 5 to 10 minutes eggs spawn and are fetilized. Each female sea lamprey will lay up to 60,000 eggs, approximately 14% of which will likely be deposited in the nest (where they have a 90% chance of survival). Once these reproductive tasks are complete, both the males and females will die within a few days. A few adults won't spawn eggs due to a lack of essential substances, the degeneration of internal organs, and/or the accumulation of poisonous metabolites.
The Great Lakes Fishery Commission (GLFC), a joint organisation of the US Fish and Wildlife Service and the Department of Fisheries and Oceans Canada, in an effort to control the sea lamprey population in the Great Lakes, has determined the three most vunerable points during a sea lampreys life:
- Concentrated groups of sea lampreys are vunerable during migration and the sedentary phase. The GLFC has determined that migration can be stopped by low-head barriers placed close to the mouths of lakes the sea lamprey must pass through. Sea lampreys are capable of jumping just over two feet, though other migratory fish can jump farther, and so aren't held back by the low-head barriers. The downside to controlling the sea lamprey population through this method is that its effects might not be noticeable for years.
- During the metamorphosis from ammocoete to juvenile, the GLFC has concluded that the sea lamprey is more vunerable to being screened out of the water or electrocuted.
- The larval stage of the sea lamprey's life (ammocoete) is thought to be the most vunerable, as any action taken would have an immediate effect on the sea lamprey population.
Currently, in addition to low-head barriers, the GLFC is using two chemicals to control sea lamprey populations. The first is called TFM (3-trifluoromethyl-4-nitrophenol) which, in low concentrations, affects little else other than sea lampreys. Most fish are able to process and expel TFM without feeling its harmful effects but sea lampreys can suffer from circulatory and respiratory collapse as a result of TFM intake. TFM usage began in 1958 and has been placed in tributary streams at 3 to 10 year intervals (depending on lamprey statistics) since then with a noticeable affect. Some worry, however, that surviving lampreys may be building up a resistance to TFM.
The other chemical being used to control sea lamprey population is Bayer 73. Bayer 73 is typically added to the water in combination with TFM at the rate of 0.5 to 2.0% of TFM. The advantage of this combination is that the total lampricide requirement can be reduced up to 50%. Bayer 73 is added in such a small amount because it can affect other fish and it is 43 times more toxic than TFM.
Another method of controlling the sea lamprey population that has been proposed is increasing the market for it. For several centuries, sea lamprey was considered a delicacy in Europe, though today the fish has little market appeal. The eel-like appearance and creepy-looking mouth of the sea lamprey makes the creature seem quite unappetizing to humans, regardless of whether or not it tastes any good.
When compared to most modern fish, the sea lamprey appears primitive and largely undeveloped. Lampreys are one of the oldest extant types of vertebrates, having branched off from other types of vertebrates about 500 million years before the group that lead to modern fish and remained relatively primitive in terms of its vertebrate complexity. From a neurobiological standpoint, sea lampreys are proto-vertebrates: Their nervous system are composed of standard vertebrate cell types and strucutres but contain far, far fewer neurons than most modern vertebrates. On the other hand, the sea lamprey's nervous system is also considered, as one website put it, "robust," allowing for types of long-term partial animal experiments that have typically only been possible with invertebrates. Sea lampreys also have sensors in their tail skin that can not only sense water movement but light as well. In April of 2001, for example, scientists managed to remove the brain of a lamprey and hook it up to a simple mechanical body with light sensors. When light was shined on certain parts of the mechanical body, the lamprey's brain reacted as though its natural body had sensed the light and moved the mechanical body accordingly. Gruesome but fascinating.