Countershading - The Camouflage Pattern of Fish and Marine Animals

In Girl in the Glass, when the Valencia defies gravity, Declan wonders how they’ll avoid detection from people looking up. Officer Riggs points out the Valencia’s new paint job, the hull’s light blue color specifically chosen to address this concern. Riggs explains:

“We painted the Valencia’s hull light blue for a reason, to match the sky. Fish are colored the same way, lighter on the bottom, camouflaging themselves from even deeper fish.

The phenomenon Riggs is describing, where fish have a darker color on their dorsal (upper) side and a lighter color on their ventral (lower) side, is known as countershading. This coloration pattern serves as a form of camouflage, making the fish less visible to both predators and prey. 

Countershading works by making the fish, or the Valencia, blend into the background. When viewed from below by an even deeper fish, or in the case of the Valencia, by people on the ground, the lighter bottom side helps the fish (and Valencia) blend in with the brighter surface of the water or the sky. The Valencia doesn’t need to worry much about being spotted from above, but for fish, a darker top side blends in better with the darker depths of the water or the seabed, protecting them from predators above them.

Countershading also helps predators sneak up on their prey. Sharks, one of nature’s most perfect apex predators, exhibit this coloration pattern. The Valencia also benefits from countershading’s predatory value, the Clypeate trying to give the Obturavi as little warning as possible.

Bluefin Tuna with countershading

Sea mammals like dolphins are also countershaded

Countershading also helps predators like sharks

Countershading - dark on top, light on bottom