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Title: Towards alternative control strategies against Saprolegnia diclina on Salmonid (Salmo salar) eggs
Author: Van den Berg, Albert Hendrik
ISNI:       0000 0004 2740 2982
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2012
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Saprolegnia infections on eggs and fish are a major problem in the Scottish salmon farming industry. Saprolegniosis, as the disease is called, is characterised by fluffy white or grey growth on the gill and skin of fish, or on eggs. Until the turn of the century, the disease was kept under control using malachite green. The discovery of carcinogenic and teratogenic properties however, caused the dye to be banned from use in commercial aquaculture. As a result, new control methods are now sought after. Landcatch Ltd, a specialised salmon breeding company co-funded a PhD Case-studentship that was created to look for alternative control measures. Measures investigated in this thesis were on a chemical, biological or genetic basis. Within the hatchery, Saprolegnia diclina was found to be the species responsible for egg infections. Three other Saprolegnia species were discovered, including Saprolegnia parasitica, a notorious pathogen of fish. Survey of incubators with infected eggs show the presence of families of salmon whose eggs might be less susceptible to Saprolegnia infection. A potential biocontrol agent (Pseudomonas fluorescence spp) was isolated from hatchery samples, and was found to secrete molecules with strong anti-Saprolegnia properties. The investigated molecule turned out not to be a common antibiotic and is subject to further identification. Within this thesis, we report for the first time on the use of appressoria by an oomycete for the infection of a member of the animal kingdom. Specialised infection structures were found to attach themselves to the egg and subsequently weakening the attachment site by secretion of proteolitic enzymes. The resulting weak spot can then be penetrated by hyphae, leading to the death of the egg. Findings and recommendations within this Thesis have been implemented by Landcatch, and have lead to significant reductions in mortality of Salmon eggs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Salmon farming