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Rezultaty
DNA sequences from different Gyrodactylus species, populations and forms display variations that can be exploited to develop diagnostic tests that can be perceived as more objective than microscopic examination. In addition, for some species or types, such as G. salaris, G. thymalli, G. teuchis and G. salaris-like G. x, morphological characters may fall within the same range, and therefore alternative methods are required for laboratories that do not have personnel that are skilled and experienced in Gyrodactylus examinations. Sequences from variable region V4 of the small subunit ribosomal RNA (rRNA) gene, the rRNA internal transcribed spcer (ITS) and intergenic spacer (IGS) have been determined and described, along with the methodology used and the clones produced. Variations between most Gyrodactylus species and between G. salaris and G. salaris-like G. x can be demonstrated by restriction enzyme digestion of amplified ITS. Differences between G. salaris and G. thymalli and between different G. salaris populations occur within the IGS.
The degree of variation within the ITS and IGS have been assessed and do not significantly affect the use of these regions of the genome for identification of species and strains, respectively.
An alternative region of the genome has also been examined and appears promising for species discrimination. The exploitation of these results requires molecular biology technology in order to provide objective molecular markers for the different forms of Gyrodactylus examined.
The specificity of different species and types of Gyrodactylus parasites for different salmonid host species was examined. The classical form of Gyrodactylus salaris was found to be the only parasite type that showed rapidly and unlimited population increase on Atlantic salmon. Other species and types of Gyrodactylus, such as G. thymalli, G. teuchis, and G. salaris-like G.x can be maintained on Atlantic salmon and other salmonid fish, but do not show unlimited increase in intensity of infection and therefore are unlikely to pose a threat to these fish. These other parasites can be difficult to distinguish from the classical form of G. salaris, particularly by morphological examination. The effect of immunosuppression on host susceptibility was also assessed and found to result in increased improved ability of parasites to reproduce on otherwise resistant fish stocks. The results of the host specificity and pathogenicity experiments carried out during this project are being disseminated in the scientific literature relevant to subject descriptor codes A06 and A40.
The current state of the art in this field is extremely limited with respect to G. thymalli, and the results generated here are the first such studies on G. teuchis and G. salaris-like G.x. These results provide clear evidence for the relative risk to salmonid species of these parasites and also yield valuable information on the differences between G. salaris and G. thymalli. The exploitation of these results requires molecular biology technology in order to provide objective molecular markers for the different forms of Gyrodactylus examined.
The presence and prevalence of various Gyrodactylus species in both natural watercourses and aquaculture facilities was determined through systematic and intensive sampling and examination.
The occurrence of G. salaris in Norway and Denmark was reaffirmed and this species was also obtained from Russia and Sweden. Other, harmless, species were obtained from Scotland, Norway and Denmark and from other countries not participating in the project; France, Czech Republic, Ireland and England.
The results of the sampling programme carried out during this project are being disseminated in the scientific literature.
The current state of the art in this field is very variable in different countries, with the Gyrodactylus status in Norway well known, status in Scotland monitored since 1991, and status in Denmark not known in detail until now.
These results provide valuable information on the occurrence of various Gyrodactylus species in these and other countries.
Exploitation of these results requires knowledge of local conditions to design relevant sampling programmes to monitor Gyrodactylus status.
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