Korean Lamprey

The Korean lamprey (Lethenteron morii) is a small, non-parasitic jawless fish native to freshwater streams of the Korean Peninsula. It belongs to the genus Lethenteron, a group of lampreys found across parts of East Asia, and is closely related to other small non-parasitic species in the region. Unlike parasitic lampreys, the adult Korean lamprey never feeds, instead relying on energy reserves accumulated during a long larval stage spent buried in stream sediment. Like all lampreys, it belongs to the ancient jawless fish order Petromyzontiformes, lacking true jaws, a bony vertebral skeleton, and paired fins. The species remains entirely within freshwater throughout its life cycle and is considered sensitive to stream habitat degradation.

• Small, slender, scaleless body, yellowish-brown to olive-grey in color
• Circular sucking-disc mouth with weak, blunt teeth, typical of non-parasitic lampreys
• Seven round gill openings behind the head
• Low dorsal fin set toward the rear of the body
• Adult length typically 15-20 cm, small compared to parasitic lamprey species

The Korean lamprey is distinguished from other regional lamprey species mainly by subtle differences in tooth arrangement, dorsal fin shape, and its consistently small non-parasitic adult size, features examined closely by researchers when identifying East Asian Lethenteron lampreys.

Korean lampreys live entirely in freshwater, inhabiting small, clean streams and upper river reaches across the Korean Peninsula. Larvae burrow into soft sand or silt substrate in slow-flowing pools and backwater areas, where they filter-feed for several years before metamorphosis. Adults briefly occupy gravel riffle habitat with moderate flow to spawn following their short non-feeding adult stage. The species favors cool, well-oxygenated headwater streams with minimal pollution or siltation, and its distribution can be affected by stream channelization, damming, or agricultural runoff. Because of this sensitivity, its presence is often regarded as an indicator of good freshwater stream quality in the region.

Korean lamprey larvae spend the majority of their multi-year life cycle burrowed in soft stream sediment, filter-feeding on algae, diatoms, and organic detritus with little movement. After metamorphosis, the short-lived adult stage does not feed, surviving instead on energy reserves built up as a larva. Adults migrate a short distance to suitable gravel riffle habitat, where they construct a simple nest, spawn, and die within a matter of weeks. As a non-parasitic species, it never attaches to other fish for feeding, unlike some of its parasitic Lethenteron relatives elsewhere in East Asia. Within its stream habitat, the species contributes to organic matter processing and serves as prey for other aquatic predators.