[2] This fish leech occurs in freshwater locations in the Holarctic and Neotropic regions and is found in northwestern Europe and in North America.

[3] It is also present in some marine environments such as the Baltic Sea where it mainly parasitises shorthorn sculpin and flounders.

Hosts include salmon (Salmo salar), brown trout (Salmo trutta), European eel (Anguilla anguilla), charr (Salvelinus alpinus), gudgeon (Gobio gobio), bream (Abramis brama), perch (Perca fluviatilis), Prussian carp (Carassius gibelio) and common carp (Cyprinus carpio).

When satiated, it releases its grip and sinks to the bottom, hiding among stones or submerged plants while digesting its meal.

[2] The mid-gut and adjoining mycetomes (pouches), contain symbiotic bacteria which help with the digestion of blood, provide additional nutrients, and prevent the entry of pathogens.