Résumé
In recent years, shellfish farming of Haliotis tuberculata, the European abalone, has started in Irelandand France. In general, cold waters protect the gastropod from bacterial and parasitic diseases but the shellcolonization by boring polychaetes is an important problem causing a reduction of marketability and growth rate.During this study conducted in Brittany on animals reared with different culture techniques we showed that age andfarming methods are determinant factors that influence the intensity of infestation. The polychaetes collected fromabalone shells belonged to two different families: Spionidae, as referred in previous works (Clavier, 1992) andSabellidae, reported for the first time in European abalone. Morphological studies indicated that Spionidaepolychaetes belonged to different species of the genera Polydora/Boccardia. The taxonomic identification ofSabellidae at genus/species level was not reached by morphological exam, but at least two distinct species seemed tobe present. Prevalence and intensity of infestation by Sabellidae were low but a single specimen was able to causevery heavy lesions of the shell. The results of this study showed that prevalence is positively linked to host age andthat the farming system can strongly influence the infection intensity of boring polychaetes: very low in in-land farms,where water is filtered and hygienic procedures are routinely applied to tanks, and higher in mariculture, inparticular in polyculture and areas with a low water turnover, with slow growth and performance indexes reduction