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Why do some salmon have white flesh?

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My friend recently caught a Coho with white flesh in the Douglas Channel. I didn't know they could have white flesh! Please explain.

Professor Salmon's response:

Great question! Chinook salmon have the most variation in pigmentation, but this variability (e.g., white flesh) isn't limited to them -- as your friend found out firsthand.

The familiar orange-pink colouration in salmon is produced by carotenoids, which appear as photosynthetic natural pigments. Carotenoids are produced only by phytoplankton, algae, plants, and a limited number of fungi and bacteria. Salmon absorb carotenoids as they eat, and usually the carotenoids are deposited in their muscles, resulting in that familiar orange-pink colour.

However, it's genes that determine the distribution and storage of carotenoids.

In some salmon, the gene(s) responsible for depositing carotenoids into muscle are simply missing or present in low amounts. When this happens, salmon flesh won't turn the colour we're accustomed to seeing, and instead appear white, cream, or marbled.

Professor Salmon