Eel Sucker

Petromyzon marinus is a jawless fish characterized by a cartilaginous skeleton, cylindrical body, and a distinctive circular, tooth-lined oral disc used to attach to host fish and feed on their blood and tissue. As an anadromous species, it spends most of its adult life in marine waters before migrating into freshwater rivers to spawn, after which adults die. Larvae, known as ammocoetes, live buried in river sediment for several years, filter-feeding on organic matter—a process that contributes to nutrient cycling and water filtration in river ecosystems.

Adults also serve as a food source for various predators and, historically, for humans.

The species has a wide range across the North Atlantic, occurring in coastal and freshwater systems throughout Western Europe, Scandinavia, the British Isles, and eastern North America, with additional records extending to parts of the Mediterranean, North Africa, and isolated occurrences elsewhere.

Its decline stems from multiple compounding pressures: dams and river barriers block access to historic spawning grounds; water pollution and chemical contamination degrade both larval nursery habitat and water quality; sedimentation from land-use changes smothers spawning beds; overfishing and incidental bycatch reduce adult populations; and shifting water temperatures linked to climate change affect spawning timing and larval development.

Conservation responses include dam removal and fish passage projects in parts of Europe and North America, water quality monitoring and pollution control programs, and research into population genetics and migratory patterns to inform management. Some regions have introduced fishing restrictions or quotas.

Despite these measures, population trends remain unclear due to limited monitoring data, and the cumulative, ongoing nature of the threats suggests continued vulnerability without substantial improvements in river connectivity and water quality.

Adults are parasitic in marine and large freshwater environments, while larvae (ammocoetes) burrow in soft sediments of freshwater rivers and streams. Adults require access to clean, gravel-bottomed rivers and streams for spawning.