Vertebral abnormalities in free-living Chinook salmon (Oncorhynchus tshawytscha, Walbaum) in New Zealand

ABSTRACT

Spinal abnormalities are common in farmed Chinook Salmon in New Zealand. We report spinal abnormalities in adult Chinook salmon which were predominantly hatchery reared and released as smolts and which we term free-living. We compare these to rates seen in farmed New Zealand salmon. 101 free-living adult salmon were radiographically assessed for spinal curvatures (lordosis, kyphosis, scoliosis; LKS) and other vertebral abnormalities. Severity of abnormality was assessed on a three-point scale. Abnormal vertebral bodies were detected in 88.1% of free-living salmon. Spinal curvatures were the most common abnormality type with 83.2% of fish showing this abnormality but only one free-living Chinook had LKS of severity greater than 1. Farmed Chinook salmon are reported to have LKS rates of 29% with 18% of LKS abnormalities of severity greater than 1. These results suggest that free-living Chinook salmon frequently develop spinal abnormalities, but these abnormalities are less severe than those observed in farmed salmon.

KEYWORDS:

• Spinal abnormalities
• vertebra
• free-living Chinook salmon
• New Zealand
• Oncorhynchus tshawytscha

Acknowledgements

We are grateful to the National Institute of Water and Atmospheric Research (NIWA), Fish and Game New Zealand, Salmon Smolts New Zealand Co and New Zealand King Salmon, Nelson New Zealand for assistance in obtaining samples of free-living and farmed salmon. NIWA is also thanked for providing the digital X-ray unit and technical assistance enabling taking radiographs of Rangitata River fish samples.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Peter S. Davie http://orcid.org/0000-0002-5394-7519

Additional information

Funding

This research was supported by Ministry for Primary Industries (New Zealand) Sustainable Farming Fund [13/003: Reducing malformations in farmed King salmon]; New Zealand King Salmon and Skretting Australia (PhD scholarship to Adelbert de Clercq).