Lordotic-kyphotic vertebrae develop ectopic cartilage-like tissue in Senegalese sole (Solea senegalensis)

Lordosis and kyphosis are curvatures of the vertebral column that commonly affect Senegalese sole (Solea senegalensis) under intensive rearing conditions, constituting a problem for the aquaculture industry by increasing labor and operation costs and consequently reducing profits. However, no studies have yet addressed microanatomical changes in vertebral column curvature in this species. We have conducted histological analyses in order to determine the alterations at tissue and cellular levels in these deformities. Development of an ectopic cartilage-like tissue within bone matrix at the growth regions (contact area between two vertebrae) of affected vertebrae was observed in lordotic-kyphotic fish. As previously suggested, the increase in strain supported by deformed vertebrae may trigger the onset of metaplastic tissue formation through an osteochondroprogenitor precursor from the condensation of mesenchymal cells or by trans-differentiation of (pre-)osteoblastic cells to a chondrocytic lineage. The possibility of a notochord contribution, as well as the molecular events related to bone stress and bone types in terms of cellularity, are also discussed.