Gyrodactylus unicopula Glukhova, 1955, from young plaice Pleuronectes platessa L. with notes on the ecology of the parasite

A population of Gyrodactylus unicopula Glukhova, 1955, is described from the gill filaments of young plaice from a nursery ground on the north-west coast of Scotland. The seasonal incidence of this parasite was followed by sampling the 1965 year class of plaice at intervals of from one to three months from April 1965 to April 1967. The level of intensity is usually low and shows no progressive increase, although the fish are shown to be capable of supporting much higher populations of the parasite, which suggests the existence of some mechanism controlling the level of intensity in the natural population. The distribution of G. unicopula on the filamentous surface of the gills is shown in detail. χ² analyses indicated no significant association or antagonism between this parasite and two ciliates commonly found on the gills of the same population of plaice. Gyrodactyliasis, the disease caused by parasites of the genus Gyrodactylus, is discussed with special reference to marine fish farming.