Why are Fish Silvery?

Why is it common for fish to have a bright silvery appearance? Usually, if a fish is colored like this their home is well-lit waters and they spend time near the surface. Silvery fish tend to school together and the light flashing off their scales makes it harder for predators to focus in on a single fish. The silvery appearance also acts like camouflage when they are against the sunny light-reflected surface of the water.

Consider how sea-run trout and salmon often change colors to a silvery chrome when they head into the ocean and how their colors have advantages for what environment they are in.

This silvery appearance common in bait fish is also probably why shiny lures like spoons and spinners are effective on predatory fish. The flashes of light make it harder for predatory fish to truly identify your lure and also serve as an attractant as it's remeniscent of flashes from a bait school.

Ichthyology