The fish would appear to be reddish brown in color at a water depth of 15 meters due to the scattering and absorption of light under water.
Colors are nothing more than different wavelengths that get reflected by an object. In water these waves travel differently, and some of the wavelengths gets filtered out by water sooner than others depending upon their absorption. Lower energy waves gets absorbed first, after that the red disappears at about 20 feet. Then comes Orange at around 50 feet. Then it is yellow at about 100 feet. Green stays a bit longer and blue the longest, which is the reason things look bluer the deeper you go.
To learn more about scattering of light under water refer to:
https://brainly.com/question/12563240
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