From embryo to adult, Atlantic salmon remodel their internal axial skeleton.

What is it about?

All vertebrate animals begin development by forming a pressurized internal skeleton, called a notochord. The notochord is a continuous rod that runs from the skull to the tail, and it is built of large, fluid-filled cells packed inside a shell of fibrous proteins. In most vertebrates, including the Atlantic salmon studied here, the notochord becomes segmented as bony structures, called vertebrae, are built. During all of development, from egg to adult, the hydrostatic notochord has important functions, stiffening the body and serving as an elastic spring during swimming. The transformation of the notochord during development is thus a complicated process, one involving changes in anatomy, function, and, in salmon, changes in a complex life cycle.

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Why is it important?

Salmon are fascinating animals: born in rivers, maturing in the sea, and returning upstream to reproduce. Each habitat presents different challenges to the developing salmon, from life in a constrained egg, followed by movements in gravel, to foraging in the open river, to migrating thousands of miles. The ability to bend the body to wiggle and swim is key at all stages, and the key structure of the body that facilitates this movement is the axial skeleton, the backbone. The axial skeleton begins in the early embryo as a continuous notochord. The notochord is a hydrostatic skeleton, where internal fluid resists compression and its external fibrous skin resists tension. To the notochord bony vertebrae are added, and the hydrostat becomes part of a composite mechanical structure with joints. We map the changes in the structure and function of the notochord from egg to adult.

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