The bluegill, scientifically named Lepomis macrochirus, is a common freshwater fish in North America, belonging to the sunfish family, Centrarchidae. This species is often called “bream” or “brim.” Identifying the bluegill accurately requires focusing on its unique body shape, specific fin structure, and distinct coloration patterns.
General Body Profile and Dimensions
The bluegill possesses a body that is deep and compressed from side to side, giving it a characteristic disk-like or slab-sided appearance. This shape is pronounced in the bluegill, which typically reaches lengths between 4 and 12 inches, though specimens can occasionally exceed 4 pounds.
The bluegill’s mouth is relatively small and terminal, positioned at the front of the head. The upper jaw (maxilla) does not typically extend past the front edge of the eye’s pupil. The dorsal fin is continuous, consisting of a spiny front section and a soft-rayed rear section. The pectoral fins, located behind the gill cover, are long and pointed, often reaching past the eye if bent forward.
Key Identifying Colors and Patterns
Bluegill coloration can vary based on their habitat, water clarity, and spawning status. The back and upper sides are generally a dark olive-green to bluish color, fading into lighter blue or silver along the flanks. The belly typically displays a warmer hue, ranging from yellow to orange, which becomes bright orange or reddish in breeding males.
Most bluegill display six to eight faint, dark vertical bars along their sides. The most reliable field mark is the flexible, black “ear flap,” a posterior extension of the gill cover. This opercular flap is uniformly dark, lacking the colored trim found on related sunfish. A dark spot is also present at the base of the soft-rayed portion of the dorsal fin.
Distinguishing Bluegill from Closely Related Species
To identify a bluegill, compare its features against other common sunfish, such as the Pumpkinseed and the Green Sunfish. The Bluegill’s ear flap is uniformly black without any light-colored margin. In contrast, the Pumpkinseed (Lepomis gibbosus) has a distinct, bright red or orange spot along the edge of its black ear flap.
The size of the mouth also serves as a reliable separator from the Green Sunfish (Lepomis cyanellus). The Green Sunfish has a much larger mouth, with its upper jaw extending well past the center of the eye. The bluegill’s small, terminal mouth is adapted for feeding on small invertebrates, while the Green Sunfish’s larger gape reflects a more predatory diet. Finally, the Bluegill often exhibits distinct blue-green coloring on its cheeks and chin, which gave the species its common name.