Fish leech
Piscicola geometra
The fish leech is a slender, cylindrical leech that lives as an ectoparasite on various freshwater fish. It reaches a length of about 2 to 5 centimeters and has a conspicuously large posterior sucker that is wider than the rest of its body. The coloration is usually greenish or brownish with a characteristic light, net-like pattern on the back. It prefers oxygen-rich, standing or slow-moving waters and is a proficient swimmer.
Details
Identification
Cylindrical body, very large posterior sucker, two pairs of eyes on the anterior sucker, net-like pigmentation.
Social behavior
Solitary; only comes into contact with conspecifics for reproduction.
Diet
Feeds exclusively on the blood of freshwater fish such as carp, barbel, or pike.
Hunting strategy
Lurks on aquatic plants (ambush predator), attaches itself to passing fish upon contact.
Spawning substrate
Solid substrates such as stones, aquatic plants, or wood for depositing cocoons.
Overwintering
Overwinters in the sediment or remains active on hosts in deeper, frost-free water zones.
Ecology
Ecological role
Ectoparasite contributing to the natural regulation of fish populations; intermediate host for blood parasites.
Natural predators
Predatory fish, dragonfly larvae, and other carnivorous invertebrates.
Competitor species
Other fish parasites such as fish lice (Argulus) or other leech species.
Ecosystem service
Part of the aquatic food web and contributor to biodiversity.
Threats
Eutrophication of water bodies, oxygen depletion, and chemical pollutants.
Scientific profile
Profile
Distinguishing features
The most important feature is the presence of two large, circular suckers. The posterior sucker is significantly wider than the maximum body width and is used for firm attachment to the substrate or host. The anterior sucker bears two pairs of eyes. The rhythmic, undulating swimming motion is also characteristic.
Diet
Blood from various freshwater fish, including cyprinids (carp-like), percids (perch-like), and salmonids (trout-like).
Reproduction
Hermaphrodites with mutual fertilization. Eggs are laid in small, oval, brownish cocoons (approx. 1-2 mm) attached to hard substrates. Development is direct without a larval stage.
Role in food web
Primarily functions as a parasite; mass infestations can weaken host fish and create entry points for fungal or bacterial infections. Serves as prey for larger invertebrates.
Protection & threats
Main threats
Severe water pollution, chemical contamination (pesticides), loss of suitable spawning substrates for host fish, and destruction of riparian vegetation.
Conservation measures
Protection and restoration of watercourses, maintenance of natural fish fauna, and promotion of diverse riparian vegetation.