Communicating Through Color
One of the main reasons for the popularity of coral reef fishes in the aquarium is their dramatic and dazzling colors. The underlying reason for these colors is their role in communicating messages between fish in their natural environment. Colors may change over the course of a fish's life but, to make sure each individual fish within a species is "speaking" the same color "language," the signal each color pattern conveys remains the same. Given the clarity and brightness of the water typically found on reefs, visual communication is of primary importance to the fish that live there. Coral reef fishes use color to convey information on a variety of things, from sexual maturity to their mood, and from toxicity to the "social" status of some species, such as cleaner wrasses, as parasite removers.
Can coral reef fish change color?
The colors displayed by fish are often highly variable, switching throughout their lifetimes as they mature into adults or change sex.
For example, emperor angelfish change their color patterns totally from juvenile to adult, and surgeonfish and tangs use colors to draw attention to their sharp spines. Colors also vary over shorter periods, say while camouflaged fish seek to match their background or when fish need to communicate their mood, as seahorses do, or to accentuate a display.The incredible flasher wrasses put on an amazing display during courtship, while barcheek wrasses use rapid color changes to communicate aggression. Many fish advertise for the attention of a cleaner wrasse. Rapid color change allows fish to communicate obviously and effectively and, in such a visually dominated environment as the reef, it is little surprise that so many fish use it.
Do the bright colors of reef fish make them targets for predators?
It seems obvious that a vividly colored fish would stand out to a hunting predator, yet new research suggests that this may not be the case after all. Clearly, we cannot see the world as fish do, but from what we know of the structure of their eyes, it seems highly likely that yellow is an excellent color for camouflage on the reef. What is more, many fish can see in the ultraviolet spectrum. In fact, it is very likely that coral reef fishes make extensive use of ultraviolet light. The point is that fish and other reef animals see the world completely differently than us, perceiving different colors, and a prey animal that appears to us to stand out may be far less obvious to a fish predator.
How do fish create and change their color?
Al The colors displayed by fish are governed by chromatophores - cells that cover the animal and contain color pigments.There are several types of chromatophores, each responsible for a different element of fish coloration. Perhaps the most important ones are the melanophores, which contain the black pigment melanin and therefore affect the darkness of. say, a banding pattern. Melanophores. especially, are capable of rapid change in response to the fish's mood or to the environment. If these cells distribute the pigment evenly across themselves, the fish appears dark, but if the pigment is gathered up into clumps, the skin appears lighter.
Other chromatophores include the erythrophores, which hold carotenoids and affect the levels of yellow to red coloration. Indophores, containing guanine, are responsible for the silvery shimmer of some fish. Beyond these chromatophores, reef fish may also use their protective mucus layer to accent or to hide some colors. The mucus can absorb certain parts of the spectrum, especially ultraviolet, and the fish has some measure of control over the extent of this mucus layer.