Sea lamprey

The sea lamprey (Petromyzon marinus) is a parasitic fish found in the Northern Hemisphere.

Because of its unique way of feeding, some people call it the "vampire fish." It is a member of the lamprey family and is known for its eel-like body. Unlike many other fish, the sea lamprey lacks paired fins. Its mouth is round and works like a suction cup. This sucker-like mouth is often as wide as, or even wider than, the lamprey's head.

To feed, the lamprey uses a specific biological process. It attaches its sucker-like mouth to the skin of a host fish. Inside the mouth, many concentric rows of sharp teeth surround a rasp-like tongue. The lamprey uses this tongue to rasp away the host's tissue. To make feeding easier, the lamprey produces a fluid called lamphredin. This substance prevents the victim's blood from clotting. Most host fish die from excessive blood loss or from an infection.

The life cycle of the sea lamprey is anadromous. This means they live in salt water or large lakes but migrate into rivers to spawn. During spawning, females deposit many eggs into nests. These nests are built by males in the substrate of streams with moderately strong currents. Once spawning is finished, the adult lampreys die. The larvae, known as ammocoetes, live in the sand and silt of quiet water downstream. They spend several years in freshwater, feeding on plankton and detritus. Eventually, they undergo metamorphosis to become adults that can migrate to the sea.

The sea lamprey has a very interesting physiology that helps it survive. As it moves between fresh and salt water, it must manage its internal salt and fluid levels. This process is called ionoregulation. The lamprey uses the membranes on its gills to control the movement of ions. As larvae move toward the ocean, their gill membranes change to become less permeable. This helps them withstand higher salinity. The lamprey can also tolerate high levels of urea in its blood. This is helpful when it feeds on elasmobranchs, such as sharks and rays, which have high urea levels.

In the Great Lakes region, the sea lamprey is considered a major pest. It was likely introduced through the Erie Canal in 1825 or the Welland Canal in 1919. Originally, Niagara Falls acted as a natural barrier to keep them out of the upper lakes. However, the construction of the Welland Canal allowed them to bypass the falls. They invaded Lake Erie in 1921, Lake Michigan in 1936, Lake Huron in 1937, and Lake Superior in 1938. In these waters, they attack native fish like lake trout, lake whitefish, chub, and lake herring. A single lamprey can kill 40 pounds of fish during its 12 to 18 month feeding period.

Scientists use many methods to control lamprey populations in the Great Lakes. One common method is using a selective pesticide called TFM, or 3-trifluoromethyl-4-nitrophenol. This chemical is applied to rivers to manage the population. Another method involves building physical barriers in rivers to block lampreys from migrating upstream to spawn. While effective, these barriers can sometimes stop other fish species from traveling as well. Researchers are also studying lamprey pheromones. These are chemical signals that can lure lampreys to specific locations. By understanding these signals, scientists hope to find more environmentally friendly ways to control the species.

Researchers are also looking at the lamprey's genetics to understand its evolution. The genome of Petromyzon marinus was sequenced in 2013. This revealed that lampreys have unusual patterns in their DNA compared to other vertebrates. For example, northern lampreys have between 164 and 174 chromosomes, which is a high number for vertebrates. The lamprey genome is also highly repetitive, with about 35% of the assembly made of repetitive elements. Studying these genetics helps scientists understand how the lamprey's immune system works. This knowledge could eventually help protect the balance of entire aquatic ecosystems.