Gyrodactyloides bychowskii (Monogenea : Gyrodactylidae) from sea-caged Atlantic salmon Salmo salar in Scotland: occurrence and ribosomal RNA sequenceanalysis

Gyrodactyloides bychowskii has been recorded in Scottish waters for the fir st time, The parasite was found on the gills of Atlantic salmon reared in s eawater. An integrated morphological and molecular examination of the paras ite was carried out. Prevalence of the parasite was greatest in February an d declined to 0 by June in 1999. During 2000, parasites were located in Mar ch and November, An overdispersion of parasites was recorded, with intensit y of infection reaching over 200 parasites per gill arch in some fish. Para sitised gill tissue showed hyperplasia and hypertrophy but not always at th e site of parasite attachment. The internal transcribed spacer of the ribos omal RNA gene array was amplified by PCR and sequenced. This sequence share d greatest similarity with the internal transcribed spacer of Gyrdicotylus gallieni, followed by Gyrodactylus species. This is the first molecular ana lysis of this parasite and provides sequence data that may be used in compa rison of G, bychowskii from other locations or in phylogenetic analysis of this group of Monogenea.