Freshwater Shrimp

• It is one of the reference species in ecotoxicology: its locomotor behaviour is altered by very low concentrations of pollutants such as ibuprofen, which makes it an indicator of water quality.
• It is the intermediate host of the acanthocephalan worm Pomphorhynchus laevis, which manipulates its behaviour so that it is eaten by fish; the infection is recognised by the bright orange colour of its gills.
• The genus Gammarus has more than 200 described species, making it one of the richest among the crustaceans.
• It is a key shredder in European rivers: it breaks down the leaf litter that falls into the water and puts that organic matter into circulation, a central role in the river food web.
• The male practises precopulatory guarding: he grips the female with his gnathopods and holds her for up to a week, because he can only fertilise her immediately after she moults.
• That guarding is energetically costly, and leads to fights between males.
• Several parasites manipulate its behaviour. The acanthocephalan Pomphorhynchus laevis makes it seek out light and the smell of fish instead of avoiding them, which is exactly what suits the parasite in reaching its final host.
• It is a standard bioindicator species in ecotoxicology because of its sensitivity to pollutants.

Skeleton type

Invertebrate - articulated calcareous exoskeleton (crustacean)

Habitat and environment

Freshwater habitats throughout Europe: rivers, streams and also caves, where individuals lose much of their colouring

Sexual maturity

Sexual dimorphism appears with maturity: males are larger and develop a bigger second gnathopod

Sources consulted: Wikipedia (Gammarus pulex); Pinkster (revisión del género Gammarus); Labaude et al. 2015, Parasites & Vectors 8; ScienceDirect (Gammarus pulex overview); ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid

Best time: All year round, under stones and among the submerged leaf litter of rivers and streams