How do trout change color?

As we've been coming around to classes this December to talk about adaptations, or a trait that helps an organism survive, we've been talking about camouflage methods as a way for animals to adapt to their environment and noticing colors and markings forming on the trout in our tanks. But as we notice parr marks forming on the lateral line of our brook and brown trout, it's interesting to think about how the trout actually change colors.

Many fish, along with reptiles and amphibians, use cells called chromatosomes to alter their appearance. Pigment granules within each chromatosome can be constricted, or pressured, causing the granules to spread out and become more visible. All the colors found in fresh water fish are made up of three pigments, Eyrthrin (red), Melanin (black) and Xanthin (yellow), each occurring in different chromatosomes. All the colors found in freshwater fish like trout, are a mixture of these pigments created a marking or colouring on the fish- like black and yellow chromatosomes coming together to make brown coloring on the trout. 

As we watch the trout in the fry or parr stage, continue to observe as the colors and patterns become even more visible and keep in mind the scientific process creating these fascinating colors that are simultaneously beautiful to look at and useful for camouflage strategies.