Fouling of invasive red swamp crayfish, Procambarus clarkii (Girard, 1852) by the zebra mussel, Dreissena polymorpha (Pallas, 1771) in Lake Trasimeno, Italy

Observations of Procambarus clarkii fouling, by alien zebra mussels (Dreissena polymorpha) in Lake Trasimeno (and in the laboratory) are recorded. Results agree with previous reports that zebra mussels can be found, if only occasionally, on most parts of the swamp crayfish body, with a general preference for the ventral surface, and in this case, the pereopods. The frequency of colonization on P. clarkii in the wild varied from 0 to 4%; much lower than other crayfish species (e.g. 65% in Orconectes limosus or 12–24% in O. rusticus). Adults of both sexes were colonized equally. Multiple zebra mussels observed on individual crayfish were unexpectedly high; this may relate to poor crayfish condition and may also explain the only colonization of a live crayfish individual recorded in the laboratory.