Kokanee salmon, also known as landlocked sockeye salmon, are an interesting species that undergo some fascinating changes during their spawning period. One of the most notable transformations is the change in coloration, where their bodies become red and their heads turn green. This change in color serves several important purposes for the kokanee salmon.
Firstly, the vibrant red coloration of the body and the green coloration of the head are visual signals that help the salmon attract a mate. During the spawning period, male kokanee develop a humped back and a hooked jaw, known as a kype. These physical changes, combined with the bright red color, make the males more attractive to females. The red color is a result of the absorption of carotenoid pigments, which are naturally occurring compounds found in the salmon’s diet.
Carotenoids are pigments that are commonly found in plants, algae, and some bacteria. They are responsible for the red, orange, and yellow colors seen in many fruits and vegetables. Kokanee salmon acquire carotenoids through their diet, primarily by consuming small aquatic organisms, such as zooplankton and crustaceans, which contain these pigments. The carotenoids are then stored in the salmon’s flesh, giving it a reddish hue.
Interestingly, while carotenoids are responsible for the red coloration of the salmon’s flesh, they do not directly contribute to the green coloration of the head. The green coloration is actually a result of a different pigment called biliverdin, which is formed during the breakdown of hemoglobin in the salmon’s blood. Hemoglobin is the protein responsible for carrying oxygen in the blood, and as the salmon prepare for spawning, they undergo physiological changes that result in the breakdown and reabsorption of their blood cells. This process leads to the release of biliverdin, which imparts a green color to the head and other areas of the salmon’s body.
It is important to note that the color change in kokanee salmon is not exclusive to those that migrate to the sea. Unlike their anadromous counterparts, which migrate to the ocean and then return to freshwater to spawn, kokanee salmon spend their entire lives in freshwater. However, they still exhibit the characteristic silvery coloration before spawning. This silver color is a result of light scattering off the scales of the salmon, creating a shiny appearance.
As the spawning period approaches, kokanee salmon begin to absorb their scales, which exposes the underlying flesh and allows the carotenoid pigments to become more visible. This process is believed to enhance the visual signals used for mate selection, as well as potentially providing some protection against predation. The bright red coloration of the kokanee salmon’s flesh can serve as a warning signal to predators, indicating that the fish is nearing the end of its life cycle and may not be in optimal condition for consumption.
The red coloration of kokanee salmon during spawning is a result of the absorption of carotenoid pigments, which are acquired through their diet. The green coloration of the head is caused by the release of biliverdin during the breakdown of blood cells. These color changes serve as visual signals for mate selection and may also provide some protection against predation. Despite not migrating to the sea, kokanee salmon still undergo these color transformations, albeit without the initial silver coloration seen in their anadromous counterparts.