Sunfish, the common name for a family of mostly small freshwater fish; also the name of a large ocean fish.

Freshwater sunfish are noted for their nest-building. The male hollows out a depression in the sand where the female lays her eggs. After fertilizing the eggs, the male guards the nest and the newly hatched young. One of the best-known species of sunfish is the pumpkinseed, or common sunfish, which grows up to nine inches (23 cm) long. It is found in lakes throughout much of the eastern half of the United States and is often taken by fishermen. Some species, such as the 3 1/2-inch (9-cm) blue-spotted sunfish and the 1- to 1 1/2-inch (2.5- to 4-cm) banded pygmy sunfish and everglades pygmy sunfish, are popular aquarium fish.

The ocean sunfish, also called headfish, is a huge creature often described as a large head with two fins. It is not related to freshwater sunfish. A full-grown specimen may be 11 feet (3.4 m) long and weigh 2,000 pounds (900 kg) or more. The tail is almost indistinguishable. The ocean sunfish is dark gray above with silvery sides and white belly. It is found in tropical and temperate seas throughout the world, usually in open waters.

Why Are Sunfish Named After the Sun?

Sunfish are named after the sun because many of them are round and brightly colored—just like the sun. Sunfish such as the bluegill and pumpkinseed have bright yellow or orange bellies. Sunfish make up a family of about 30 freshwater fish.

These bony fish live in lakes and streams across North America. Most sunfish grow to only 8 inches (20 centimeters) long and weigh under 1 pound (454 grams). Other members of this family, including largemouth bass, can grow up to 2 feet (61 centimeters) long and weigh over 15 pounds (6.8 kilograms).

Beware of the name sunfish, however. It also refers to a group of strange-looking ocean fish with giant heads. They are also known as molas. These fish often rest on the surface of the water in sunny weather. Unlike freshwater sunfish, these ocean sunfish weigh 1,000 pounds (450 kilograms).

Freshwater sunfish make up the family Centrarchidae. The pumpkinseed is Lepomis gibbosus; blue-spotted sunfish, Enneacanthus gloriosus; banded pygmy sunfish, Elassoma zonatum; everglades pygmy sunfish, Elassoma evergladei.

The ocean sunfish is Mola mola of the family Molidae.