They are generally small to medium-sized fish. Bluegills are generally carnivorous. When other food is in short supply, they will also eat algae. These nests are shallow, circular depressions and are frequently in areas with gravel bottoms. Often many males build nests in a small area.
Females lay eggs in the nests.
The males then guard the eggs until they hatch. These references have more information on bluegills. If this interested you, you might be interested in these other Internet resources on fish. The State Fish was selected by schoolchildren in 1986.