Bony Fish

More than 90 percent of the world’s fish have skeletons made of bone instead of cartilage. Bony fish appear in all sizes, shapes, and colors imaginable. They can be as small as guppies, or as massive as an 880-pound (400-kg) tuna. Some are shaped like bullets, some like pencils, and others like flat plates. On the reef, bony fish display a rainbow of colors and an almost endless variety of markings.

Bony Fish (image from NOAA)
Bony Fish (image from NOAA)

When people envision a coral reef fish, most think of parrot fish. These large, brightly colored animals have teeth that are fused to form a parrotlike beak, giving them their name. They are usually found feeding in shallow reef water where they scrape off alga that is growing on top of the coral skeletons, or chew up the skeletons to get to the algae within. Since skeletal material is extremely hard, the digestive systems of parrot
fish have developed unique adaptations to handle it. Teeth in their throats grind the calcium carbonate and release the algae. The algae travel on through the digestive system where they are broken down, absorbed, and used for nutrition. The pulverized coral is defecated as sand.

Because they physically remove reef material, parrot fish play important roles in sculpting the reef structure. In one year, a parrot fish can convert about five tons of reef into sand. Their activity is a major part of the bioerosion of the reef and part of the destructive forces that reduces its size. At the same time, the activities of parrot fish help keep the coral animals alive. As grazers, they prevent large mats of algae from covering the coral and smothering it. In this way, they help build up the reef structure.

Parrot fish have developed a unique strategy to protect themselves from predators. At night, they find a crack or crevice in the reef that they can use as a “bedroom.” Once inside, the fish spend about 30 minutes secreting sticky mucus which they wrap around their bodies, similar to a cocoon. The mucus seals in the odors of the parrot fish and prevents nighttime predators from finding them by smell.

One of the many species of parrot fish is the queen parrot fish (Scarus vetula) that grows to about 2 feet (60 cm). Like some other species of parrot fish, this one has two color patterns that are associated with its unusual sexual development. All of the young adult parrot fish are drably colored females, but some of them change into colorful blue and yellow males. A few develop into supermales, very brightly colored fish that have the first opportunity to spawn with the females and therefore the best chance to pass their genes to the next generation.