What is a Butterflyfish?

A butterflyfish is a member an omnivorous group of about 120 species of saltwater fish in the Chaetodontidae family. They are sometimes confused with freshwater butterflyfish which are in an entirely different family. They are native to reefs in the Atlantic, Indian, and Pacific Oceans. Most species are distinctively colored and patterned. Some of these fish are solitary until they find their lifelong partner. These colorful fish are a favorite of saltwater aquarium hobbyists.

The ocean reefs that butterflyfish call home tend to be under 59 feet (18 meters) deep. The oblique banded butterflyfish is one of only a few species that dive down to as much as 590 feet (180 meters). For the most part, these fish stay close to their home ranges. At night, the fish hide among the coral, their colors fading to blend in with their surroundings.

This species of fish is most often between 5 to 9 inches (12-22 cm) long. The exceptions to this are the lined butterflyfish and the saddle butterflyfish, which can be up to 12 inches (30 cm) long. All of the fish in this family have very thin bodies, which allow them to fit into the narrowest reef crevices. Their dorsal fins are uninterrupted and their tail fins may be rounded but never forked.

These fish are most often found in shades of blue, yellow, red, or orange although some are have dull coloring. The coloring is thought to be used as a means of communication between different species. Most of these colorful fish have eyespots on their flanks and bands over their eyes. This patterning acts to confuse predators who are not sure which end of the fish to attack.

The majority of butterflyfish mate for life. Mated fish spawn by releasing eggs into the water. Once the eggs hatch, the couple raises their young together. If a mated fish dies, sometimes the partner will die shortly afterwards.

The fry, or newly hatched fish, are born with bony plates that extend the length of their body. As they mature, the plates fall off. Only one other fish family has fry who go through an armored stage like this.

Butterflyfish are popular with people who own saltwater aquariums. Keeping these fish can be a difficult prospect, however, because many species eat coral polyps and sea anemone. It is for this reason that many aquarium enthusiasts obtain the species that eat a wider variety of foods including zooplankton.