Lampreys are ancient, jawless fish that have existed for over 340 million years. These eel-like creatures belong to the order Petromyzontiformes, a distinct lineage. Their cartilaginous skeletons, rather than bony structures, set them apart from most fish. Lampreys possess a single nostril atop their head and seven gill pores on each side. While they may superficially resemble eels, lampreys are not closely related to them.
The Ammocoete Stage: Filter Feeding Larvae
Lampreys begin as larvae, known as ammocoetes, which differ from their adult forms. These blind, worm-like larvae typically burrow into the soft sediment of freshwater streams, where they remain for several years. During this larval phase, ammocoetes are filter feeders. They draw water through their mouths using a muscular velum and pharyngeal muscles, creating a current that brings in microscopic organisms, detritus, and algae.
Food particles become trapped in a mucosal membrane within their pharynx and are then transported to the digestive tract. This filter-feeding mechanism supports their growth and development, allowing them to accumulate energy reserves. The ammocoete stage can last from three to seven years, or up to eight years for some species like the sea lamprey, before they undergo metamorphosis into their adult form.
Adult Lamprey Diets: Parasitic Feeders
Many adult lamprey species are parasitic. These lampreys attach to host fish, and occasionally marine mammals, using their suction-cup mouths. This oral disk is lined with sharp, horn-shaped teeth, which help them maintain their grip. Once attached, a toothed, file-like tongue rasps a hole through the host’s scales and skin.
Lampreys then feed on the host’s blood, bodily fluids, and muscle tissue. To facilitate feeding, they secrete an anticoagulant enzyme, such as lamphredin, into the wound, which prevents the host’s blood from clotting. This allows continuous feeding, which can last for 12 to 18 months in species like the sea lamprey. Host fish include lake trout, salmon, lake whitefish, walleye, and sturgeon. A single parasitic sea lamprey can destroy up to 40 pounds of fish during its feeding period.
Adult Lamprey Diets: Non-Parasitic Species
Not all adult lampreys are parasitic. Some species, known as non-parasitic or brook lampreys, do not feed at all during their adult lives. These species rely entirely on energy reserves accumulated during their ammocoete (larval) stage. Their adult phase is primarily dedicated to reproduction.
After metamorphosis, non-parasitic adults migrate to spawning grounds, reproduce, and then die shortly thereafter. Their mouths, while present, are not adapted for feeding, and their teeth are often vestigial or weak. This non-feeding adult stage represents a distinct life history strategy, contrasting with their parasitic relatives.