Vertebral column deformity with curved cross‐stitch vertebrae in Norwegian seawater‐farmed Atlantic salmon, Salmo salar L.

Abstract

Pathological changes in the vertebral column of farmed Atlantic salmon in Norway have been reported since the 1990s. Based on the characteristic radiographic findings, we here present a vertebral column deformity named “curved cross‐stitch vertebrae” that mainly affects the middle aspect of the vertebral column. Sixty fish, from the west/northwest coast of mid‐Norway, were sampled at slaughter and examined by radiography, computed tomography (CT), necropsy, macrophotography, and histology. The vertebral deformities were radiographically graded as mild, moderate, or marked. The main differences between these grades of changes were defined by increased curving of the peripheries of endplates, reduced intervertebral spaces, and vertical displacement of the vertebrae. The curved rims of endplates were located peripheral to a continuous and approximately circular borderline. The CT studies revealed small, multifocal, hypo‐attenuating, round to crescent‐shaped areas in the notochord, compatible with the presence of gas. Additionally, histology revealed that the axial parts of endplates had circular zones with perforations, through which either notochordal tissue prolapsed into the vertebrae or vascularized fibrochondroid proliferations extended from the vertebrae into the notochord. Inflammation was present in many vertebral bodies. To the best of our knowledge, this is the first report of gas in the notochord of fish.

A case of melanization after intramuscular vaccination in Atlantic salmon (Salmo salar L.)—Possible causes and implications

“…Vaccine‐related side effects have been described as peritonitis (Koppang et al, 2005; Mutoloki et al, 2004, 2006), auto‐immunity (Koppang et al, 2008), reduced growth (Aunsmo, Larssen, et al, 2008; Mutoloki et al, 2004), spine deformities (Aunsmo, Guttvik, et al, 2008; Holm et al, 2020; Trangerud et al, 2020), downgrading and macroscopic visible changes in fish abdomen (Aunsmo, Guttvik, et al, 2008). Melanization of muscle tissue and granulomatous changes that may pose a risk for reduced fillet quality are not mentioned in the Summary of Product Characteristics (SPC) for Clynav® (EMA, 2017).…”

Anatomical and pathological characteristics of ribs in the Atlantic salmon (Salmo salar L.) and its relevance to soft tissue changes

“…Insufficient diet giving phosphorus, ascorbic acid and vitamin D deficiency has been proved to affect bone development and bone weakness in both mammals and teleosts (Baeverfjord et al, 1998; Darias et al, 2011; Roberts et al, 2001). In salmonids, vertebral deformities have been reported as the most frequent skeletal abnormality, with several different malformations in the vertebral column such as lordosis, kyphosis and scoliosis, vertebral fusions and cross‐stich vertebra (Fjelldal et al, 2012; Trangerud et al, 2020; Witten et al, 2009). Thus, most studies have focused on changes in the vertebra, and not the ribs.…”

The effect of vaccine‐associated cross‐stitch vertebrae pathology on growth of farmed Atlantic salmon

“…Size of fish at time of vaccination has previously been associated with vertebral deformities (Aunsmo, Guttvik, et al, 2008; Aunsmo, Larssen, et al, 2008; Berg et al, 2006, 2012). A type of spinal deformity named “curved cross‐stitch” vertebrae (Trangerud et al, 2020) was recently described. In brief, affected vertebrae exhibit distinctive pathological changes with axial and radially distributed lesions of the compact bone of vertebral endplates (Fjelldal et al, 2007; Holm et al, 2020; Trangerud et al, 2020; Witten et al, 2009).…”

“…A type of spinal deformity named “curved cross‐stitch” vertebrae (Trangerud et al, 2020) was recently described. In brief, affected vertebrae exhibit distinctive pathological changes with axial and radially distributed lesions of the compact bone of vertebral endplates (Fjelldal et al, 2007; Holm et al, 2020; Trangerud et al, 2020; Witten et al, 2009). Cross‐stitch vertebrae was first recognized as a problem in commercial production of Atlantic salmon in Norway during the winter harvest season 2016–2017.…”