Lampreys are jawless fish (agnathans) representing one of the oldest surviving lineages of vertebrates. Their life cycle involves distinct developmental stages, each necessitating different methods for gathering nutrients. The dietary habits of lampreys change dramatically as they transition through metamorphosis, shifting from a stationary, microphagous lifestyle to a mobile, sometimes parasitic one.
Feeding Habits of Larval Ammocoetes
The initial larval phase is known as the ammocoete, which can last from three to fifteen years. Ammocoetes live a sessile existence, burrowed into the soft sediment of freshwater streams and rivers. They adopt a suspension feeding strategy, drawing water through their pharynx to capture microscopic food particles.
The diet consists primarily of detritus, such as decaying plant material, often reaching over 90% of their gut contents. They also consume microscopic organisms, including algae (particularly diatoms) and bacteria suspended in the water column. This extended larval period is essential for accumulating the energy reserves necessary for their upcoming transformation.
Specialized Adult Mouthparts and Attachment
Upon metamorphosis, the lamprey develops the specialized oral apparatus for adult feeding. The adult lamprey features a large, circular oral disc that functions as a powerful suction cup for attachment to surfaces or hosts. This disc is lined with numerous keratinous teeth that help secure the lamprey firmly to its target.
The mechanical process relies on a piston-like tongue located within the oral disc. This tongue is equipped with horny plates (laminae) that move in a rhythmic, rasping motion. The teeth on the tongue, which vary by species, are used to drill and scrape away host tissue after attachment.
The Parasitic Diet of Adult Lampreys
Many lamprey species, such as the sea lamprey (Petromyzon marinus), engage in a parasitic feeding strategy as adults. These species are hematophagous, meaning their primary diet consists of the host’s blood and bodily fluids. The lamprey attaches to a host fish, such as large teleost fish or sharks, using its suction disc and rasps through the scales and skin to reach underlying tissues.
Parasitic lampreys secrete an anticoagulant, lamphredin, from their buccal glands. This secretion prevents the host’s blood from clotting and contains lytic properties that help break down tissue. Some parasitic species are “flesh-feeders” that consume muscle, while others are “blood-feeders.” The morphology of their tongue teeth is adapted for either gouging flesh or efficiently rasping for blood. Feeding can lead to significant wounds, energy loss, and death for the host, often through secondary infection.
The Non-Feeding Adult Life Cycle
Not all lampreys adopt a parasitic lifestyle after metamorphosis; over half of the approximately 38 extant species are non-parasitic as adults. These species, often called brook lampreys, cease feeding entirely after metamorphosis. They lack the necessary gut development and robust feeding structures to sustain themselves.
The adult existence of these non-feeding species is dedicated solely to migration, sexual maturation, and reproduction. Their survival depends entirely on the lipid and protein reserves accumulated during their multi-year larval phase. This non-trophic period lasts for several months before they spawn and die, ending their life cycle.