The application of new biosystematic techniques in the discrimination of the genus Gryodactylus (monogenea) on samonoid fish
Prior to 1989 the total number of Gyrodactylus species recorded for all British freshwater fish numbered 20. The fauna present on the British Salmonidae was poorly documented and frequently not identified to species level. The European free market, created in 1992, resulted in legislative changes al...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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University of Stirling
1993
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| Online Access: | http://hdl.handle.net/1893/26679 http://dspace.stir.ac.uk/bitstream/1893/26679/1/shinn-thesis.pdf |
| Summary: | Prior to 1989 the total number of Gyrodactylus species recorded for all British freshwater fish numbered 20. The fauna present on the British Salmonidae was poorly documented and frequently not identified to species level. The European free market, created in 1992, resulted in legislative changes allowing the movement of live fish stocks, albeit under strict disease monitoring conditions, into the UK. One stipulation maintains that the fish stock be free of the ectoparasitic monogenean Gyrodactylus salaris Malmberg, 1957, a parasite made notifiable in the UK in 1987 (Diseases of Fish Act, 1937) owing to its pathogenicity and damage to Norwegian salmon populations in 38 rivers. Although this parasite has been reported since 1957 throughout mainland Europe, its occurrence in the UK was unknown. This project set out to make a national survey of British salmon ids and investigated 250 sample sites, examined four salmonid hosts, Atlantic salmon Salmo safar, brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss and Arctic charr Salvelinus alpinus. Seventy of the sites were found to be positive for Gyrodactylus. Distinctions were made between wild and farmed fish and prevalence, abundance and intensity data collected for comparison. Species determination within the genus Gyrodactylus is based upon subtle differences in hook morphology and has long posed a taxonomic problem. The discrimination of collected specimens was based on two platforms. The initial approach used classical morphometrics from the light microscope, the results being processed using multivariate analyses to separate species. The second approach analysed morphometric data collected from scanning electron micrographs. This was made possible by the development of a sclerite release technique utilising a source of ultrasound to liberate hooks from surrounding tissue and a subsequent flotation stage which permitted flat preparations. Sonication of fresh and frozen material retained the structures that would be lost by enzymatic digestion. The ... |
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