The occurrence and distribution of Myxidium giardi Cépède, 1906 in wild and cultured European eels, Anguilla anguilla L., in England

Abstract. Myxidium giardi was found in wild and cultured eels. The prevalence rate in elvers was 77% in the River Torridge (Devon), 80% in the River Parrett (Somerset) and 90% in the River Ouse (Yorkshire). Adult eels from the River Ouse had a prevalence rate of 53%, Cultured fingerlings and adults had a prevalence rate of 60% and 1% , respectively. There was an apparent age-related pattern in the organ location of the histozoic trophozoite: an initially high prevalence of kidney trophozoites which gradually decreased with age; in the gills of elvers there was a low prevalence of histozoic trophozoites which increased in the adult stage. Histozoic trophozoites were also found in the stomach and intestine of elvers and fingerlings. A qualitative estimate of trophozoite numbers in each organ of elvers is given. The coelozoic trophozoite of M. giardi in the gall bladder of elvers and fingerlings is also described for the first time.