Gyrodactylus derjavinoides sp. nov. (Monogenea, Platyhelminthes) on Salmo trutta trutta L. and G. derjavini Mikailov, 1975 on S. t. caspius Kessler, two different species of Gyrodactylus – combined morphological and molecular investigations Göran Malmberg 1*, Catherine M. Collins 2 , Carey O. Cunningham 2 and Behiar J. Jalali 3 1 Department of Zoology, Stockholm University, S-106 91 Stockholm, Sweden; 2 FRS Marine Laboratory, P.O. Box 101, Victoria Road, Aberdeen, AB11 9DB, UK; 3 Veterinary Department, Research and Science Branch, Islamic Azad University, P.O. Box 14515 775 Teheran, Iran Abstract The paper deals with two morphologically similar but molecularly clearly different species of Gyrodactylus: G. derjavinoides sp. nov. on Salmo trutta trutta L. in Western Europe and G. derjavini Mikailov, 1975 collected on Salmo trutta caspius Kessler in Iran. The new species is described and its opisthaptoral hard parts compared to those of G. derjavini. Our molecular analy- sis of G. derjavinoides and G. derjavini confirmed that the morphological differences between them are species differences and not intraspecific variations. Phylogenetic analysis using the ITS rDNA region placed both species within the subgenus G. (Limnonephrotus) and within the G. wageneri-group, quite in accordance with morphological results. The two species, how- ever, did not cluster as sister taxa. The correspondence between molecular-based clades within G. (Limnonephrotus) and the morphological shapes of marginal hooks within these clades are discussed. The importance of combined molecular and mor- phological analyses when describing or redescribing Gyrodactylus species is stressed. Key words Platyhelminthes, Monogenea, Gyrodactylidae, Gyrodactylus sp. nov., fish, Salmo trutta, Western Europe, Iran * Corresponding author: goran.malmberg@zoologi.su.se Introduction In 1975, the disastrous problems with Gyrodactylus salaris Malmberg, 1957 in salmon farms and natural waterways in Norway were first revealed. Fear of spread of the parasite prompted investigations to increase knowledge of gyrodac- tylids infecting salmonids not only in Norway but also in other areas with salmonid populations and salmonid farming. The Gyrodactylus fauna on salmonids was sparsely known and the limited knowledge of differences defining Gyrodactylus spe- cies caused problems with species discriminations, e.g. Gyro- dactylus species on Salmo trutta trutta. In Western Europe the species here described as G. derjavinoides was called, i.a. G. derjavini 1 . The first account of G. derjavinoides was in 1958, from S. t. trutta in a fish farm in Western Sweden (Malmberg 1973, 1993; fig. 7). Its opisthaptoral hard parts were documented according to Malmberg (1970) and its protonephridial system mapped. The species was found to be a typical member of the subgenus G. (Limnonephrotus), species group G. wageneri. In 1972, the species was also found on S. t. trutta in natural water and on farmed Oncorhynchus mykiss (Walbaum), Salvelinus alpinus (L.) and S. fontinalis (Mitchill). Since then specimens of the species have been documented from many different Skra Stefaæski DOI: 10.2478/s11686-007-0016-1 © 2007 W. Stefañski Institute of Parasitology, PAS Acta Parasitologica, 2007, 52(2), 89–103; ISSN 1230-2821 1 For previous recording of G. derjavinoides as G. derjavini see footnote in the species description section. Unauthenticated Download Date | 7/28/18 8:22 PM