Ukrainian Brook Lamprey

The Ukrainian brook lamprey (Eudontomyzon mariae) is a small, non-parasitic jawless fish native to freshwater streams and small rivers across Eastern and Central Europe, including drainages of Ukraine, Poland, Romania, and neighboring countries. It belongs to the genus Eudontomyzon, a group of European lampreys that includes both parasitic and non-parasitic species. Unlike its parasitic relatives, the adult Ukrainian brook lamprey never feeds, instead relying entirely on energy reserves built up during a long larval stage spent buried in stream sediment. After metamorphosis, adults live only a few weeks, during which they spawn once and then die. The species remains entirely within freshwater and is sensitive to stream pollution and habitat disturbance, making it a useful indicator of clean water.

• Small, slender, scaleless body, yellowish-brown to olive above, paler below
• Circular sucking-disc mouth with weak, blunt teeth, unlike sharp-toothed parasitic lampreys
• Seven round gill openings behind the head
• Low dorsal fin, often slightly notched into two sections, set toward the tail
• Adult length rarely exceeds 20 cm, smaller than most parasitic river lampreys

The Ukrainian brook lamprey can be told apart from parasitic Eudontomyzon relatives by its smaller adult size and much weaker, blunter dentition, since a non-feeding adult has no need for teeth capable of piercing host fish.

Ukrainian brook lampreys live entirely in freshwater, inhabiting small, clean, well-oxygenated streams and the upper reaches of rivers across Eastern and Central Europe. Larvae burrow into soft sand or silt deposits in slow-flowing pools and backwaters, where they remain for several years filter-feeding. Adults briefly occupy gravel riffle habitat with moderate current to spawn after metamorphosis. The species prefers unpolluted headwater streams with stable banks and minimal siltation, and its distribution has contracted in areas affected by channelization, damming, or agricultural runoff. Because of its sensitivity to water quality, its presence is often used as an indicator of healthy stream ecosystems in the region.

Ukrainian brook lamprey larvae spend several years buried in soft stream sediment, filtering algae, diatoms, and organic detritus from the surrounding substrate and water column, rarely leaving their burrows. Following metamorphosis, adults emerge with functional eyes and a sucking disc used solely for gripping stones and mates, since the non-feeding adult stage lasts only a few weeks. During this short period, adults migrate a short distance to gravel riffles, where they construct a shallow nest, spawn communally, and die shortly afterward. As larvae, the species contributes to processing organic matter within small stream ecosystems and serves as prey for other stream-dwelling predators.