Camouflage and mimicry
Looking like something else, such as sand, weed or a more dangerous fish, to hide from predators or prey.
Also: mimicry, crypsis
Fish hide in many ways. Flatfish change colour to match the sea floor. Stonefish and scorpionfish look like weed-covered rocks. The leafy seadragon of southern Australia trails leaf-shaped flaps that make it look like drifting kelp. Some fish copy others: harmless filefish copy toxic pufferfish, and a fang blenny mimics the cleaner wrasse to get close to its victims. The mimic octopus is not a fish, but it imitates lionfish and flatfish. Juvenile batfish drift on their sides to look like dead leaves.