Bluegills are a widely dispersed member of the sunfish family and a close relative to the largemouth bass. The bluegill's body is fairly compressed, oval or rounded, with a small mouth and head and pointed pectoral fins, all of which are characteristic of the sunfish family.
A bluegill's coloring will vary greatly from one body of water to the next, ranging from olive, dark blue, or bluish purple to yellow and green on the sides with a blue background. There are six to eight vertical bars on each side, which may or may not be prominent, depending on the sex of the fish and the time of year. The gill cover extends to create a wide black flap and is not surrounded by a lighter border as in other sunfish. Dark blue streaks are located on the lower cheeks between the chin and gill cover. (This is where the bluegill gets its name.) Bellies are almost always a deep yellow or orange in color.
Colors become more prominent in breeding males and bright blue and orange are widespread, along with black pelvic fins. Females and young bluegill are less brightly colored.
Because bluegills prefer not to chase their food, their principal food source is slow-moving aquatic insects. However, the also enjoy small crayfish, fish eggs, minnows, snails, and worms. Bluegills are opportunistic feeders, meaning they will take advantage of whatever food source is present in a given area. If necessary, they will also consume aquatic plants.
Young bluegills will focus on insects, worms, and crustaceans almost exclusively in shallow water. Adult bluegill will feed at various depths depending upon water temperature and food availability. Thus, they seek food on both the bottom and the surface of the water. During the hottest periods of the year, they often reside in deeper water and then come shallow to feed at sunrise and sunset.
Originally, bluegills were native to the eastern half of the United States from southeastern Canada to northeastern Mexico. As a result of intentional and unintentional introductions, bluegill are now common throughout the entire United States. The greatest abundance of bluegill is found in the large region running from the St. Lawrence River to the Great Lakes to the Mississippi River basin east and south to the Atlantic Ocean, the Gulf of Mexico, and the Rio Grande River. However, bluegill can be found in some numbers in every state. Bluegills have also been introduced in Europe, South Africa, Asia and South America.
Bluegills are found in lakes, rivers, reservoirs, creeks, streams and ponds throughout their native and introduced ranges and can thrive in nearly any water that provides food, optimum temperature and adequate spawning grounds.
They prefer environments with warm water and plenty of vegetation and will spend a great deal of time in shallow areas. Their ideal temperature range is between 65 and 72 F but bluegills can tolerate temperature levels much higher or lower. Many bluegills are caught through the ice, as well as during the hottest days of summer.
Bluegills prefer calm, protected waters and will be found most frequently in shallow, weedy environments that harbor adequate numbers of insects and small minnows. In flowing water, they will seek slow-moving streams and rivers, especially around pools. The habitat preferences for bluegill are generally the same as that for the largemouth bass, and anywhere you find largemouth bass, bluegills will likely be nearby.