In male salmons, pink salmon and sockeye
salmon, dorsal ridges develop markedly with sexual maturity. Although past
studies have published that the dorsal ridge is packed with a tissue mass of “cartilage”
known as fibrocartilage based on gross observations, and the “cartilage theory”
has been supported by domestic and international salmon experts. However, our
research group has analyzed the dorsal ridge of pink salmon from a
microanatomical perspective.
The results revealed that the bone at the
center of the dorsal ridge is a hard bone called the “incomplete intraneuronal
spine”, which becomes longer, thicker, and at a greater angle to the body axis
with maturation. In addition, cartilage tissue previously reported to be
present around the bone was not observed and was actually “sparse connective
tissue”.
It has also been found that the main
components of this tissue are mostly type I collagen, which is the same type of
collagen contained in skin, and water. Furthermore, mature male individuals had
higher levels of 11-KT in their blood than immatures or females, suggesting the
involvement of male sex hormones in the formation of the dorsal ridge.
