Four stages characterizing vertebral fusions in Atlantic salmon

Until recently, the molecular development of spinal deformities in fish has received relatively little attention and most studies have been largely descriptive. Due to economical matters of the industry, previous deformity studies were primarily based on radiographic findings, histological staining and field studies to reveal factors inducing deformities. Consequently, few deformities have been explored beyond the level of association with particular causative factors. However, accumulated studies on intensive production regimes and incidence of deformities have been followed by more advanced studies on vertebral development and bone biology. A better understanding of cellular and molecular events during bone development in teleosts should enable us to better characterize the pathology, define particular requirements and enable us to minimize the occurrence of bone disorders. In this review, four hallmarks in the cellular and molecular development of vertebral fusions in Atlantic salmon (Salmosalar) are described.