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    Magnetic resonance imaging shows spinal curvature in Chinook salmon (Oncorhynchus tshawytscha) is associated with chronic inflammation of peri-vertebral soft tissues.
    (John Wiley and Sons, Inc., 2024-03-01) Lovett BA; Firth EC; Perrott MR; Munday JS; Pontre BP; Lydon A-MP; Symonds JE; Preece MA; Herbert NA
    Chinook salmon (Oncorhynchus tshawytscha) farmed in New Zealand are known to develop abnormal spinal curvature late in seawater production. Its cause is presently unknown, but there is evidence to suggest a neuromuscular pathology. Using magnetic resonance imaging (MRI), we evaluated the relationship between soft tissue pathology and spinal curvature in farmed Chinook salmon. Regions of interest (ROIs) presenting as pathologic MRI signal hyper-intensity were identified from scans of 24 harvest-sized individuals: 13 with radiographically-detectable spinal curvature and 11 without. ROIs were excised from individuals using anatomical landmarks as reference points and histologically analysed. Pathologic MRI signal was observed more frequently in individuals with radiographic curvature (92%, n = 12) than those without (18%, n = 2), was localized to the peri-vertebral connective tissues and musculature, and presented as three forms: inflammation, fibrosis, or both. These pathologies are consistent with a chronic inflammatory process, such as that observed during recovery from a soft tissue injury, and suggest spinal curvature in farmed Chinook salmon may be associated with damage to and/or compromised integrity of the peri-vertebral soft tissues. Future research to ascertain the contributing factors is required.
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    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.
    (Massey University, 2020) Brosnahan, Cara
    Salmon 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.
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    The effect of incubation temperature on early malformation, regionalisation and meristic characters of the vertebral column in farmed Chinook salmon (Oncorhynchus tshawytscha) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Science at Massey University, Manawatū, Palmerston North, New Zealand
    (Massey University, 2018) De Clercq, Adelbert
    Skeletal deformities are a recurrent problem in farmed Chinook salmon which limit production and have animal welfare impacts. Skeletal deformities of a variety of types are recognised especially when the external phenotype of the animal is affected. These types are well described in juvenile and adult stages of the production cycle. Which skeletal malformations affect early life stages in salmonids is less well known. Temperature is commonly manipulated in fish farming husbandry. High rearing temperatures are related to higher growth rates and in Atlantic salmon, elevated temperature has been inferred as a potential risk factor for skeletal deformities. In this thesis, malformations of the vertebral column in post-hatch to first feed life stages (500-900 degreedays) were studied in farmed Chinook salmon (Oncorhynchus tshawytscha) in New Zealand. Fish were reared at a constant 4°C, 8°C and 12°C, from fertilisation to juvenile stages. The effects of rearing fish at these temperatures on malformations of the vertebral column were studied in specimens whole-mount stained for cartilage and mineralised bone, and in histological sections. The external phenotype of post-hatch stages could be linked to internal skeletal malformations such as notochord malformations, chordacentra fusions and malformations of the associated elements. In all temperature groups, externally normal specimens could have internal malformations, predominantly fused chordacentra. Conversely, externally malformed fish usually displayed internal malformations. Specimens raised at 8°C had fewest malformations, followed by specimens of the 12°C group. Specimens raised at 4°C had the highest number of malformations. This study indicates that 8°C is the best incubation temperature of those tested. In addition, the effects of rearing temperature on morphological variation of skeletal elements such as vertebrae, vestigial ribs and vestigial elements in the caudal fin were studied. Six vertebral column regions were identified. The defining characters of each of these regions remained independent of the rearing temperature. Still, the postcranial, transitional and ural regions showed temperature sensitive meristic variation of the vertebrae, vestigial ribs, arches, epurals and uroneurals. Meristic variation can foreshadow skeletal malformations that emerge late in life and thus be significant for the early diagnosis of vertebral deformities.
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    The digestibility of blood meal protein by Chinook salmon (Oncorhynchus tshawytscha) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University
    (Massey University, 1996) Wright, Kerry Lee
    The objective of the present study was to establish whether commercial sources of dried blood meals available in New Zealand offer useful sources of digestible protein for chinook salmon. Three blood meals were evaluated to assess their suitability as ingredients in salmon feed. In vitro digestibility was determined using the pepsin and pronase digestibility assays. In vivo digestibility was determined by feeding diets to chinook salmon formulated to contain 20% dried blood meal (batch dried, ring dried or spray dried), and 80% of a basal diet and by correcting for the digestible protein supplied by the basal diet. Chromic oxide was included in the diets as an indigestible marker. The apparent digestibilities of crude protein and amino acids were determined based on samples of faeces collected after 7 days of feeding the respective test diet to chinook salmon. Feces were collected by a manual stripping of the hindgut. Crude protein contents were uniformly high, at 92.0%, 93.1% and 89.6% for the batch, ring and spray dried blood meals respectively. Amino acid contents were also generally high, with the exception of the essential amino acid methionine. All crude protein digestibility determinations ranked the blood meals as: spray dried > ring dried > batch dried. In vitro N digestibility values determined by pronase assay were 60.5%, 25.5% and 9.0% for spray, ring and batch dried bloods, respectively. The pronase assay yielded significantly (P<0.001) higher digestibility values than did the pepsin assay in the case of ring and spray dried blood meals, corresponding values for crude protein digestibility with the pepsin assay were 27.8%, 18.9% and 8.4% for spray, ring and batch dried bloods, respectively. The in vivo apparent faecal digestibility of protein in the dried blood meals determined in the chinook salmon were highest for the spray dried blood meal (68.4%), lower in ring dried blood meal (46.3%), and very low in the batch dried blood meal. The amino acid digestibilities were similarly ranked, with the difference between ring and spray dried blood meal being statistically significant for 9 of 17 assayed amino acids (P<0.05). A secondary aim of the study was an evaluation of the laboratory rat as a model animal for determining protein digestibility in the chinook salmon. Batch dried blood meal was fed to rats in an experimental design closely following that set for the chinook salmon, and the apparent digestibility of nitrogen and amino acids were determined based on sampling of ileal digesta. Ileal crude protein digestibility for this batch dried blood meal in the rat was also very low (3.9%), suggesting that the rat may be a suitable model animal for prediction of protein digestibility in chinook salmon. Differences in the protein digestibility of the blood meals appeared to be inversely related to the time spent in processing and drying. It appears that spray and ring dried blood meals may be suitable for inclusion in chinook salmon diets in partial replacement of fishmeal proteins. Keywords: Salmon, rat, protein, amino acid, digestibility, blood meal.