The axial skeleton of the siberian sturgeon. development, organization, structure and new insights on mineralization and ossification of vertebral elements

Abstract

Accurate data on axial skeleton development, structure and mineralization in Acipenseriformes are required not only to improve our knowledge on this functional region but also to know whether or not such information can help in understanding anomalies of the vertebral column in reared sturgeons. Recent data obtained using growth series of Acipenser baerii and various techniques such as X-ray microtomography, histological and ultrastructural descriptions, and solidstate NMR analyses have completed previous, fragmented information in Acipenseriformes, notably with regard to ossification and mineralization of the vertebrae. The axial skeleton is mostly cartilaginous, and each vertebra is composed of several elements organized around a persistent and unconstricted notochord. Typical perichondral bone is lately deposited around these elements during ontogeny and mineralizes. No resorption process of these mineralized structures was so far observed. A new mineralized tissue of unknown origin and function was discovered within the notochord. The nature of the mineral phase of all these structures is typical as they are mainly composed of amorphous calcium phosphate that progressively changes into hydroxyapatite. The few mineralized content of the vertebrae does not allow to explain the origin of the anomalies affecting the axial skeleton in farmed specimens. Future studies aiming to understand these pathologies should focus on (a) the mineral metabolism in order to identify variations of physiological markers with regard to environmental factors and (b) the structure and growth of the typical cartilage that constitutes the main component of the axial skeleton.