The sea lamprey is an eel-like fish with a circular mouth filled with teeth. This odd mouth naturally leads one to wonder, what does it eat? Like many other predatory fish, the sea lamprey’s diet includes other fish species, but it eats them in an unusual way. True to its other common name, the vampire fish, the sea lamprey latches on to a host fish and scrapes its skin with its teeth and tongue, lapping up blood and tissue that is loosened from its prey.
Their disk-like mouth is an oddity that alludes to a fascinating evolutionary history. This species belongs to a group known as the jaw-less fishes, Agnatha, which includes lampreys (Petromyzontiformes) and hagfishes (Myxiniformes). Agnatha is taxonomically ancient, and surviving species possess a range of ancestral traits that were once abundant on Earth. This group contains far fewer species than the jawed fish, Gnathostomata, which includes most other fish species, sharks, and vertebrates like humans. It is this relationship with fish that leads modern scientists to the conclusion that we evolved from fish.
What Are the Four Phases of the Sea Lamprey’s Life Cycle?
The sea lamprey life cycle is divided into four phases: egg, larvae, juvenile, and adult. Once the eggs are deposited in a nest, they can hatch anywhere from 10 to 13 days. From here, the sea lamprey enters the larval stage, where they exist as non-parasitic filter feeders and consume organic matter like detritus, algae, and microorganisms from the water column. During this stage, the larval sea lamprey are blind and spend their time in a burrow dug into the substrate. The larval stage can last anywhere from 3 to 10 years, depending on food availability and water temperature.
Following the larval stage, the sea lamprey undergoes a remarkable transformation where they develop eyes and undergo extreme physiological changes to tolerate salt water. During this period, they are committed to a parasitic lifestyle and emerge from their burrows in search of host fish to feed on until they become sexually mature. At this time, their digestive system breaks down, and the fish will die after spawning is complete.
Are Sea Lampreys Invasive?
Native to the eastern coastline of North America and the rivers that drain into it, the sea lamprey maintains an equilibrium within this native range. However, it was introduced to the Great Lakes and their tributaries in the 20th century following the construction of channels to facilitate the transportation of goods and people into the region. Before this event, land barriers and Niagara Falls kept the sea lamprey out of the Great Lakes. There is evidence that the sea lamprey is native to Lake Ontario. However, this assertion is debated among scientists.
Non-native species are simply organisms suddenly found outside their native range. These species can travel through natural events like storms or the deconstruction of natural barriers. Still, most introduced species arrive in novel habitats because of humans and the connections we have made globally. To be invasive, a species must pose a danger to native organisms and disrupt the natural balance of an introduced ecosystem. Sea lampreys do this by feeding on fish in droves. In many cases, multiple lamprey feed on a single fish, causing loss of blood and other bodily fluids, reducing the chances of prey survival. Additionally, the open wounds left by sea lamprey feeding are easily infected by bacteria in the water or on the fish. Their introduction has led to the extinction of at least three species in the Great Lakes.
The phenomenon where two invasive species “help” each other survive in a novel ecosystem is termed an “invasional meltdown” and can have dire consequences for native species. In the case of the sea lamprey and the Great Lakes, the introduction of the sea lamprey resulted in a reduction of large, predatory fish, which allowed other non-native species to thrive. Alewife (Alosa pseudoharengus) populations in the Great Lakes exploded due to a lack of predation, resulting in the Great Lakes’ ecology restructuring by competing with native species for food. Additionally, the alewife is a poor prey item compared to native species due to high levels of thiaminase in their bodies, which can cause vitamin deficiencies and neurological issues in predators that did not evolve to eat large quantities of alewives.
The human cost of these losses is reduced production in the Great Lakes, meaning fewer fish are caught each year for human consumption, and fewer fish are available to support wildlife, resulting in reduced commercial viability and habitat quality.
What Do Sea Lampreys Eat?
The diet of the sea lamprey varies throughout its life. Hatchlings filter organic matter from the bottom of the river and transition to a predatory diet as they age. When hunting, sea lampreys swim through the water column in search of a fish to attach to. They use their circular mouths to create suction, making them difficult to remove from the smooth skin of a fish. Once attached, they use their many circular rows of teeth and sharp tongues to scrape the fish’s skin, removing scales, skin, and flesh from the fish’s body. Additionally, their saliva contains an anticoagulant that prevents the host from clotting and facilitates prolonged feeding. This anticoagulant also slows the healing process once the lamprey is removed from the fish, increasing the chances of infection.
Are Sea Lampreys Fish?
Sea lampreys are considered fish, but they are a type of fish known as a “jawless fish.” This means their mouths lack the hinge-like mechanism found in most other species of fish and land-dwelling vertebrates. Due to their lack of jaws and other morphological traits, the sea lamprey is considered a primitive fish, possessing many ancestral characteristics not seen in most modern organisms. It is thought that agnathans, the jawless fish, were once more abundant. Still, the development of jaws gave “jawed fish” an advantage over jawless fish that allowed the group to flourish, giving rise to most vertebrates today, including humans.
Can I Fish for & Eat Sea Lamprey?
In short, yes! While sea lamprey is not readily eaten in the United States, they are a popular delicacy in Europe. Reportedly, their relative lack of bones makes them easy to process and prepare for a meal. Additionally, sea lamprey caviar makes for a pricey, luxurious hors d’oeuvres.
The process of capturing sea lamprey involves trapping them before they spawn. In North America, wildlife officials use special traps placed in stream areas where migrating sea lampreys congregate. These traps have a cone-shaped opening that lets sea lampreys in without allowing them to swim out.
How Do Sea Lampreys Reproduce?
Sea lampreys can reach sexual maturity in as little as 18 months but may take up to 5 years. Once sexually mature, adults stop feeding on fish. During the breeding season in April and June, adults migrate to rivers and streams to spawn. Males will construct a nest that takes the form of a small pit dug into the substrate, and a female will deposit as many as 100,000 eggs within it. Shortly after spawning, both adults die.
