OCCURRENCE AND IMPACT OF HETEROPOLARIA SP (PROTOZOA, CILIOPHORA) ON INTENSIVELY CULTURED PERCH (PERCA-FLUVIATILIS)

This study describes the occurrence and the impact of Heteropolaria sp . in intensively cultured perch (Perca fluviatilis). Heteropolaria sp. , in association with Aeromonas sp., form a symbiotic complex which ma y induce severe pathology in intensively cultured perch. This colonial ciliate is most frequently detected in winter when it colonizes the s piny dorsal fin of young perch and spreads all over the body in older individuals. High population density favours the propagation of Hetero polaria sp.: the infestation frequency in 40 g perch after two months of rearing at 23 degrees C was 10, 50 and 91%, at stocking densities o f 303, 602 and 1 974 fish m(-3), respectively. High temperatures and r epeated handling (e.g. sorting) also increase the risks of infestation .