No abstract

Anterior/posterior (a/p) compression of the vertebral column, referred to as 'short tails', is a recurring event in farmed Atlantic salmon. Like other skeletal deformities, the problem usually becomes evident in a late life phase, too late for preventive measures, making it difficult to understand the aetiology of the disease. We use structural, radiological, histological, and mineral analyses to study 'short tail' adult salmon and to demonstrate that the study of adult fish can provide important insights into earlier developmental processes. 'Short tails' display a/p compressed vertebrae throughout the spine, except for the first post-cranial vertebrae. The vertebral number is unaltered, but the intervertebral space is reduced and the vertebrae are shorter. Compressed vertebrae are characterized by an unchanged central part, altered vertebral end plates (straight instead of funnel-shaped), an atypical inward bending of the vertebral edges, and structural alterations in the intervertebral tissue. The spongiosa is unaffected. The growth zones of adjacent vertebrae fuse and blend towards the intervertebral space into chondrogenic tissue. This tissue produces different types of cartilage, replacing the notochord. The correspondence in location of intervertebral cartilage and deformed vertebral end plates, and the clearly delimited, unaltered, central vertebral parts suggest that the a/p compression of vertebral bodies is a late developmental disorder that may be related to a metaplastic shift of osteogenic tissue into chondrogenic tissue in the vertebral growth zone. Given the lack of evidence for infections, metabolic disorders and/or genetic disorders, we propose that an altered mechanical load could have caused the transformation of the bone growth zones and the concomitant replacement of the intervertebral (notochord) tissue by cartilaginous tissues in the 'short tails' studied here. This hypothesis is supported by the role that notochord cells are known to play in spine development and in maintaining the structure of the intervertebral disk.KEY WORDS: Notochord · Skeletal deformities · Vertebral malformations · Metaplasia · Bone · Salmon · Chondrogenesis Resale or republication not permitted without written consent of the publisherDis Aquat Org 64: [237][238][239][240][241][242][243][244][245][246] 2005 be regarded as undeformed (McKay & Gjerde 1986, Madsen et al. 2000. In Atlantic salmon Salmo salar the pronounced a/p compression of the vertebral column results in a phenotype that is characterized by a reduced fork length (FL) and increased body height, traits that result in a deformity-related high condition factor (CF). These individuals are referred to as 'short tails' (Vågsholm & Djupvik 1998).The appearance of 'short tails' is a recurrent problem in salmon farming. The prevalence can vary from year to year, from region to region, and from cage to cage. Some observations suggest that the prevalence of 'short tails' follows a smolt group, with higher frequencies in groups of fast growth smolts...

Summary Inflammation is an overall protective response and can be defined as a cellular and non specific immune response to irritation, injury, or infection leading to the local accumulation of leukocytes and fluid. In intensive farming conditions, fish are usually transported, sorted, vaccinated and subjected to stressful handling procedures which may potentially lead to local inflammation and affect the integrity of the spine. The present mini‐review aims to introduce the reader in the field of spinal deformities in salmon, propose inflammation as a risk factor for spinal deformities and emphasize the need for conducting further research in the area having an integrated and multidisciplinary perspective.

SummaryVertebral body compression is a common problem in commercial farming of Atlantic salmon. Although risk factors, such as vaccination and malnutrition, have been identified, the etiology is largely unknown. Histological studies of Atlantic salmon have shown that in a compressed deformity (platyspondyly) the length of the compact bone is reduced while the notochord start to form atypical chrondrogenic structures. In mammals, similar remodeling activities have been linked to inflammatory processes in the tissue. Hence, we wanted to investigate whether the compressed vertebrae in Atlantic salmon showed presence of local (IL-1b, TNF-a1), systemic (IgM) and chronic (MMP-13, MMP-9) immune responses (measured with quantitative PCR). Unvaccinated groups of Atlantic salmon that would later develop high or low prevalence of vertebral compression during on-growth in seawater were sampled at seawater transfer, and 3 and 6 weeks after seawater transfer. In addition, compressed and normal vertebrae from the high deformity prevalence group were sampled 44 weeks after transfer to seawater. MMP-13 was significantly up-regulated in the group that developed a high prevalence of deformity, and also significantly up-regulated in compressed vertebrae, 44 weeks after seawater transfer. In compressed vertebrae, MMP-13 was equally up-regulated in the notochord, compact bone and trabecular bone. The results of the present study suggest that MMP-13 may serve as an early indicator for bone remodeling which may lead to vertebral compression, and that there is a relationship between the development of vertebral compression and increased remodeling activities in farmed Atlantic salmon.