Diagnostic investigation into summer mortality events of farmed Chinook salmon (Oncorhynchus tshawytscha) in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Manawatū, New Zealand.

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dc.confidentialEmbargo : Noen_US
dc.contributor.advisorMunday, John
dc.contributor.authorBrosnahan, Cara
dc.date.accessioned2020-03-08T20:13:31Z
dc.date.accessioned2020-03-16T00:00:08Z
dc.date.available2020-03-08T20:13:31Z
dc.date.available2020-03-16T00:00:08Z
dc.date.issued2020
dc.description.abstractSalmon farming is the second highest value aquaculture species in New Zealand and produces approximately 88% of the global market of farmed Chinook salmon, Oncorhynchus tshawytscha (Tucker, 2014). New Zealand salmon are free of many significant diseases affecting salmonids globally (Diggles, 2016). Therefore, disease is one of the greatest threats to this New Zealand aquaculture species. Biosecurity, early detection, and characterisation of new or emerging diseases is vital for management and sustainability of the aquaculture industry. Elevated mortalities termed ‘summer mortalities’ with no cause identified have occurred in certain farmed Chinook salmon populations in the Marlborough Sounds since 2012. This study identified two potential bacterial pathogens involved in summer mortalities; New Zealand rickettsia-like organism (NZ-RLO) and Tenacibaculum maritimum. Distribution of NZ-RLO and T. maritimum within farmed Chinook salmon populations, phylogenetic analysis of these pathogens and the pathogenicity of two strains of NZ-RLO were assessed to provide an understanding of the role of NZ-RLO and T. maritimum in summer mortalities. Additionally, new diagnostic tests were developed to efficiently detect these pathogens. Identification of NZ-RLO in the summer mortalities was the first detection in New Zealand. Tenacibaculum maritimum had been reported in New Zealand previously, however it had not been associated with mortalities. This study confirmed three strains of NZ-RLO with restricted geographical distribution. Two strains of NZ-RLO were found exclusively in areas where fish experienced summer mortalities and were associated with clinical signs of disease, indicating certain strains of NZ-RLO were likely primary pathogens. Widespread distribution of T. maritimum was detected within farmed salmon and no association was found with T. maritimum and clinical signs of disease in areas experiencing summer mortalities, indicating T. maritimum was unlikely to be a primary pathogen. This study proves that laboratory exposure of salmon to two strains of NZ-RLO caused disease and mortalities however, the differences between the two strains suggest NZ-RLO2 may be more pathogenic. This study suggests NZ-RLOs are likely to be involved in summer mortalities as primary pathogens however, the interaction between the pathogens and environment is likely to have amplified the levels of mortalities during these events.en_US
dc.identifier.urihttp://hdl.handle.net/10179/15278
dc.identifier.wikidataQ112189618
dc.identifier.wikidata-urihttps://www.wikidata.org/wiki/Q112189618
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectChinook salmonen
dc.subjectPathogensen
dc.subjectNew Zealanden
dc.subjectPathogenic bacteriaen
dc.subjectFish-cultureen
dc.subject.anzsrc300903 Veterinary bacteriologyen
dc.titleDiagnostic investigation into summer mortality events of farmed Chinook salmon (Oncorhynchus tshawytscha) in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Manawatū, New Zealand.en_US
dc.typeThesisen_US
massey.contributor.authorBrosnahan, Caraen_US
thesis.degree.disciplineVeterinary Scienceen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (PhD)en_US
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