Identification of Gyrodactylus ectoparasites in Polish salmonid farms by PCR-RFLP of the nuclear ITS segment of ribosomal DNA (Monogenea, Gyrodactylidae)

Abstract

AbstractThe Gyrodactylus fauna of 274 fish taken from ten salmonid farms in Poland was sampled in 2006. Four fish species were investigated: rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta (morphs fario, lacustris, and trutta), grayling Thymallus thymallus and huchen Hucho hucho. No parasites were observed on huchen. No indications of gyrodactylosis were observed, but an unexpected parasite species diversity was found. A molecular species identification by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) of ITS1 + 5.8S + ITS2 was utilized, with addition of morphometric methods. The most frequent parasite was a new record in Poland, G. teuchis. It was present in two molecular forms on brown trout and rainbow trout, which also carried G. derjavinoides and G. truttae. Three molecular forms of G. salaris/G. thymalli were found, the standard type ITS only on grayling. A heterozygous (or heterogenic) G. salaris type described earlier in Denmark was found in seven farms on rainbow trout, and a complementary homozygous clone which differs from the standard by three nucleotides, in two farms. This homozygous form has not been recorded earlier. The PCR-RFLP results were confirmed by sequencing ITS segment from representative specimens of each type and comparing them with all available salmonid-specific Gyrodactylus sequences in GenBank. The Polish fauna with seven different Gyrodactylus clones separated by PCR-RFLP was the most diverse reported in fish farms in any country so far.