The most severe anomalies of the vertebrae are those that affect the vertebral body, such as fusion, compression and shape modifications, which, if many vertebrae are affected, can reduce the length of the fish.

Conversely, anomalies that alter the vertebral arches and spines are considered mild, since they do not affect the external shape of the fish.

It has been demonstrated in salmon that two ankylosed and compressed vertebrae can be remodeled into a single common, structured and jointed vertebra.

The fusion of vertebral bodies can progress according to two different scenarios, which we will refer to as “aggravation” and “containment”.

In the aggravation scenario, the initial fusion of two vertebral bodies leads to a compression center of vertebrae through the continuous amalgam of additional vertebrae. This fusion process of the vertebrae causes the shortening of the spine and has obvious implications for the normal movement of the animal. This type of malformation is well known for salmon and other fish species.

On the other hand, in the containment scenario, the fish are able to contain the fusion progress of the vertebral body by remodeling the fused vertebrae into a non-deformed vertebra.

REFERENCES

• Baeverfjord G, Wibe A. 2003. Short tail deformities in Atlantic salmon effect of freshwater production temperature. Beyond Monoculture. EAS special publication.
• Kvellestad, A., Høie, S., Thorud, K., Tørud, B., Lyngøy, A., 2000. Platyspondyly and shortness of vertebral column in farmed Atlantic salmon Salmo salar in Norway— Description and interpretation of pathological changes. Dis. Aquat. Org. 39, 97–108.
• Witten, P.E., Huysseune, A., 2007. Mechanisms of chondro- genesis and osteogenesis in fins. In: Hall, B.K. (Ed.) Fins and Limbs; Development, Evolution and Transformation. Chicago University Press, Chicago, 79–92.
• Witten, P. E., Obach, A., Huysseune, A., & Baeverfjord, G. (2006). Vertebrae fusion in Atlantic salmon (Salmo salar): Development, aggravation and pathways of containment. Aquaculture, 258(1-4), 164–172. doi:10.1016/j.aquaculture.2006.05.005.