The bluegill is a type of sunfish that is quite common in Wisconsin.
You can tell identify it by its characteristic blue or black "ear" that is actually an extension of its gill cover. They are a very tasty fish and are caught with such things as flies, hot dogs, raw chicken, bread, corn kernels, redworms or waxworms. They are known for their nibbling behavior, which is why they steal the bait from hooks without getting caught.
They spawn from late May to August (peaks in June), and during this time nest guarding males take on the same coloration as females in order to escape aggression from other males. Their long spawning season allows them to proliferate often resulting in overpopulation. They tend to seek out underwater vegetation for cover and they eat insects, small fish, leeches, snails, zooplankton and algae. You can find them near small docks in the summer. They have great daytime vision, but are easy prey for predators at night as they don't see well in the dark. They're a schooling fish and swim in schools of 20-30 fish. The average bluegill is 6-9 inches long and weighs 5-10 ounces. Largemouth bass, channel catfish, and turtles prey upon them which makes them great bait for catching catfish. Usually they are thought of as small lake fish, they are also abundant in natural lakes, large border rivers, and reservoirs – anywhere where there are weedy shorelines.
They are easy to catch, but you have to know where to find them. Try to find bodies of water that contain bigger fish so your trip is fruitful. Then, you have to learn their seasonal habits. They concentrate in school different areas on a lake and the locations vary with the seasons. Usually where you find them in spring is not where you will find them in the height of summer.