How Fish Manage to Live on a Coral Reef

Fish are one of the most successful groups of animals on the planet. There are over 20,000 species of fish, occupying every imaginable habitat. In each case, evolution has shaped both their appearance and their senses over countless generations and millions of years, resulting in the most effective adaptations to fit the conditions in which they live.

How are fish adapted for living on coral reefs?

Although thousands of fish species live on coral reefs, most conform broadly to a handful of body plans. Perhaps the most common shape for reef fishes is a deep, laterally compressed body, as seen in butterflyfishes, damselfishes, and angelfishes. The deep body is perfect for intricate maneuvering in the water column above the reef where the fish pick at their invertebrate prey or graze on algae with specialized mouthparts. Their wafer-thin profile also allows them to take refuge in the narrowest gaps and fissures in the reef.

The long and slender bodies of hunters, such as moray eels and trumpetfish allow them access to the heart of the labyrinth of the reef -- ideal when hunting sheltering fish and invertebrates. Other species, including blennies, gobies, and many wrasses, live close to the substrate or hug the reef as they swim and feed on benthic (bottom-living) invertebrates. Their long, thin bodies enable them to seek shelter in the reef.

Which senses do coral reef fish use most?

The waters of coral reefs are extremely clear and well lit by the equatorial sun. In addition, most reef fish live close to the surface. Under these conditions, vision is extremely important and this is reflected in the large eyes common to many of these fish. The brilliant colors, including vivid yellows and electric blues, and the dramatic patterns seen in many reef fishes are also features of brightly lit environments. Fish send bold visual signals to one another. However, to back up their vision, they also communicate using the full range of their sensory capabilities, especially smell and hearing. These are particularly important when it comes to searching out hidden prey and assessing potential mates.

How do fish use the information they gather?

In common with all animals, fish are constantly gathering information on their environment. The brain receives and decodes this information and transmits a response. So if a nocturnal predator approaches under cover of dark, any surrounding prey fish may detect a large pressure wave using their lateral line (a line of pressure
sensors along the flanks). This information is transmitted to the brain via the spinal column. In response, the brain will stimulate muscles to contract, causing the fish to swim away from the direction of the pressure wave and the predator that produced it. At the same time, the fish may gather other information about the predator; for instance, it may smell it or hear if any small stones are displaced by the predator moving from concealment. Although the brain receives all this information, the fish does not have to "think" about swimming away; moving away is a simple response.

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