A yellow seahorse (Hippocampus kuda) © Rich Lewis / Moment / Getty
Many fish have the ability to change colour and do so for all sorts of reasons. Seahorses change colour to mimic their surroundings when hiding from predators or prey (sudden, bold changes in appearance may even deter their enemies), and to communicate during courtship displays and territorial disputes.
Like other fish, seahorses change colour using small, sack-like organs known as chromatophores, which are embedded in their skin. Each chromatophore contains one of three or four pigments. Expansion or contraction of the chromatophores via tiny muscles results in different colours being displayed with varying intensity.
Chromatophores are controlled in two ways: by the nervous system (when rapid camouflage is required for predator avoidance) and by hormones (during courtship and breeding). The latter causes a slower, more controlled change, often to a brighter, less subtle.