Vertebra deformities in wild Atlantic salmon caught in the Figgjo River, southwest Norway

Abstract

Summary In order to investigate the occurrence of vertebra deformities in wild Atlantic salmon, adult river migrating salmon were caught in the Figgjo River, Norway in 2010, 2011 and 2012 (n = 24; 21; 20). Based on a definition of a deformed fish having one or more deformed vertebrae, 28 out of 65 fish were classified as deformed. The majority were minor deviations of the morphology in vertebra no 2 and in vertebrae in the ural region (52–56). Vertebral fusions were observed, the majority of which were located in the post-cranial and posterior-truncal region of the vertebral column. Fusions typically resulted in a single large vertebra with a relatively normal amphicoelous structure, albeit with multiple neural and hemal arches. This indicates that wild salmon have a strong capability of ‘repairing’ vertebra pathologies, as this stage of a vertebra deformity should not be considered as pathological anymore. Occurrence of individuals with fusions varied over the sampling period (2010: 29%, 2011: 19%, 2012: 5%). Typical deformities observed in farmed salmon, e.g. vertebra compressions in the tail region, which often cause down-grading, financial losses and reduced welfare, were not observed in any of the analysed fish and can therefore be considered as ‘farming specific’. This is the first study of vertebra deformities in adult wild Atlantic salmon, and demonstrates that these fish can develop deformities up to a level observed in harvest-size farmed salmon. However, the severity of these malformations was found to be low compared to those commonly observed in farmed salmon. The results of this study may serve as a basis for future research on vertebra deformities in Atlantic salmon.