Just when you think you’ve seen them all, there will always be one more creature either fascinating or bizarre or both that captivates our attention. If you have never heard of lampreys before, you are about to be either disgusted or interested. They are well-known among fishermen who caught a fish that already fell prey to the lampreys. What’s interesting about them is their mouth, which looks like a freaky-looking alien’s mouth, and their parasitic nature that lets them attach themselves to the prey to leisurely suck blood.

Lampreys are fish resembling eels with elongated bodies of lengths between 13 and 100 cm, but without jaws, fins or scales like normal fish.

Unlike fish, lampreys do not have vertebrae, but have a series of cartilaginous structures. On either side of their head, they have seven gill pores and a single nostril on top of their head. While some species are known to swim across open oceans, lampreys mostly live in coastal areas and fresh waters, especially in temperate regions as they are known to have low tolerance for high temperatures. They are also very energy-efficient swimmers and their swimming movements create low pressure zones that result in pulling them instead of requiring them to push through the water.

There are currently around 38 known species of lampreys still existing and among them 18 species are parasitic.

Lampreys belong to the order Petromyzontiformes and the superclass Cyclostomata. They have a very ancient lineage with fossils of its relatives dating as far back as the Silurian period, 443.8 million years ago. The parasitic lampreys are known to start feeding on other fish and other marine mammals right after their metamorphosis from larvae. However, non-parasitic species do not feed like adults and they live off the reserves they obtain when they are larva.

The characteristic feature of lampreys is their mouth, which is a toothed funnel-like opening that attaches itself to its prey and sucks the blood by boring holes through the flesh.

Instead of the jawed mouths of normal fish, these parasitic lampreys have openings lined with teeth in circles. The adults use their mouths to attach themselves to the target fish or other such animal. Then, they use their teeth to cut through the surface tissues until they reach blood and other body fluids. Attacking humans for blood is usually rare and doesn’t happen unless the lampreys are starved. Another interesting feature is how gas exchange is done. It is different from fishes and their respiratory tube is isolated from their mouths. Instead of taking the water through their mouths, they pump it in and out of their gill pouches.

Lampreys are considered great pests because they also feed on fish that are considered commercially valuable like lake trout, and getting rid of them is extremely difficult.

Lampreys are considered invasive species and are a major pest problem in North American Great Lakes where they were introduced from the sea after the construction of artificial channels. Lake Champlain and Finger Lakes near New York are also known to have high populations of lampreys. They do not have any natural enemies. Hence, they have to be controlled using special barriers that prevent the upstream movement of adults or using lampricides and toxicants that are harmless to most other aquatic life.

Despite their rather unsightly appearance and parasitic nature, they have long been used as food and are considered a delicacy in parts of Europe. 

The ancient Romans highly appreciated lampreys and during the Middle Ages, the upper classes in Europe ate them. They were also church-sanctioned food during Lent and were considered to have much meatier taste than many other fish. On March 4, 1953, the Royal Air Force had made Queen Elizabeth II’s coronation pie with lampreys. In Spain, Portugal, France, and the northern half of Finland, large lampreys are still considered a delicacy. However, their mucus and serum can be poisonous, so the lampreys must be thoroughly cleaned before cooking.
[source: wikipedia]