Abstract:
Spinal anomalies are a frequent cause of economic loss in intensive finfish aquaculture and
raise ethical concerns. Despite an abundance of knowledge, there is a lack of general consensus
about the relationships between different anomaly types, their pathologies and the factors
which contribute to their development. Novel cases must therefore be investigated
independently. The aim of this thesis was to investigate the bone and soft tissue changes
associated with the development of spinal curvature in farmed New Zealand king salmon, a
condition of unknown cause that is suspected to arise via a neuromuscular pathology.
Using X-ray radiography and two novel non-invasive tools, dual-energy X-ray absorptiometry
(DXA) and magnetic resonance imaging (MRI), it was discovered that spinal curvature
constitutes an LSK (lordosis-scoliosis-kyphosis) curvature complex which initially appears on
radiographs 7 months post-seawater transfer and induces secondary changes to the vertebral
bodies, predominantly in the form of compressions. Although DXA detected no differences in
bone mineral content, fat mass and lean mass between adult fish with and without curvature,
MRI and subsequent histology revealed that curvature was strongly associated with progressive
stages of inflammation and fibrosis of the peri-vertebral skeletal musculature and connective
tissues, particularly the horizontal septum. Feeding different commercial diets throughout
seawater production had no effect on curvature prevalence, but the results were confounded by
other factors, namely a lack of differences in feed composition, feed supply delays and
disruptions, rigor mortis, and pen movement.
Collectively, the studies provide evidence that spinal curvature in king salmon is a late-onset
neuromuscular condition that involves a chronic inflammatory process. Its development may
be related to altered mechanical load caused by high intensity exercise, excessive musculature,
fast growth, handling and transport stress, temperature, and/or insufficient bone mineralisation
during the early seawater phase. Future research should prioritise evaluation of muscular forces
applied to the spine during swimming, and the integrity of peri-vertebral connective tissues and
vertebral bone. Sustained exercise during early life, minimisation of handling and other sources
of stress, and diet manipulation may help to reduce curvature prevalence in farmed stocks while
the contributing factors are still being elucidated.