The recent development of intensive rearing of European perch Perca fluviatilis in warm water effluents revealed important pathological problems. This study gives a preliminary overview of parasites and diseases encountered in experimental perch farming. No virus has been recorded since the beginning of the experiments in 1993. By contrast, mass mortality caused by bacterial disease alone or associated with other pathogens were frequently observed. The main identified bacterial species were: Aeromonas sp., A. veronii, A. hydrophila, Streptococcus sp., Staphylococcus sp., Vibrio fluviatilis and Enterobacter agglomerans. Protozoans were the most common parasites observed on cultured P. fluviatilis. High mortality rate due to Ichthyobodo necator and Trichodina sp. may take place at different stages of perch rearing. In contrast, the infestation by Ambiphrya sp. and Heteropolaria sp. was size- or age-related; these two ciliates infested perch weighing < 1 g and > 20 g, respectively. In spite of the presence of other parasites such as Ichthyophthirius multifiliis, Hexamita spp., Gyrodactylus sp. and Argulus sp. in the rearing system P. fluviatilis does not appear to be affected. Further abnormalities or diseases inherent to intensive culture systems are also described.