Bluegill

Characteristics

A deep, slab-sided sunfish with a small mouth. Its upper jaw does not reach the front of the eye when its mouth is closed. The spiny dorsal fin has 10 spines and is joined broadly to the soft dorsal fin, but there is no notch. The pectoral fins are long and pointed and extend past the eye when they are bent in a forward position. There is usually a black spot or blotch near the base of the soft dorsal fin and a black, flexible tip on the gill cover. Its back and sides are dark olive-green with emerald and brownish reflections. The breast and belly are yellow or reddish-orange. Males in breeding colors often have a deep red, almost dark brown breast. The sides usually display vertical bars, but these are more prominent in smaller fish. The chin and gill covers are bright blue, giving the bluegill its name.

Distribution

Bluegill is the most abundant and widespread member of the sunfish family in Iowa. It is found in nearly all Iowa waters, but is more abundant in lakes and ponds than in streams and rivers. This fish is not commonly found in western Iowa streams, but is occasionally found in most eastern Iowa interior rivers. It is very abundant in the backwaters and sloughs of the Mississippi River.

Foods

Aquatic insects, small fish and crayfish.

State Record

3 lbs 2 oz; 12.88 in. - Farm Pond, Madison County, July 1986 - Phil Algreen, Earlham, Iowa

Expert Tip

Use small hooks (#8) with a long shank when fishing with live bait.

Details

Aside from farm ponds and impoundments, the largest populations of Bluegill are in warm pools and backwaters of low-gradient streams, and particularly in overflow pools along floodplains with some aquatic vegetation or other cover. Researchers note that stream populations may be sustained by fish continuously escaping from impoundments. The Bluegill is intolerant of continuous high-turbidity, siltation and flowing waters, although in Wisconsin, Bluegill were often found in moderately swift waters of streams.

Bluegills eat zooplankton when young, but switch to aquatic insects after they mature. The small-sized mouth of this fish limits the size of food particles ingested and almost dictates a diet of insects and similar small organisms. While insects remain the staple food item for adults, crayfish, snails, small fish and fish eggs are also eaten. Algae and other vegetation are eaten when normal food items are scarce. Fish lice, Argulus, have been identified in Bluegill stomach contents, showing that these fish may perform a "cleaning" function on heavily parasitized fish.

Bluegill spawn over a wide period, usually from late May to early August in Iowa, but peak spawning happens in early June. Water temperatures during the spawning season are 70 to 80 degrees. Males built nests in 1 to 4 feet of water along the shore, over diverse substrate materials, but sand and gravel are preferred. The nests are saucer-shaped depressions about 1 to 2 feet in diameter. From the shore, the colony of nests look like "elephant tracks". The aggressive males often build nests, almost touching adjoining nests. It is common to find as many as 50 nests in a 75-foot radius. Most nests are only 2- to 3-inches deep, and the male fish keep them fanned free of silt.

After nests are built, the ripe male selects a gravid female and lures her toward the nest with aggressive nudges and bites. Few females lay all their eggs in one nest, so each nest has the eggs of several females. The males guard the nest from all intruders and keep the eggs free from silt. Sometimes Bluegill hybridize with other members of the sunfish family, like Redear Sunfish, Green Sunfish and Pumpkinseed. Males make grunting noises during spawning and may be attracted to spawning areas by odor. Finer substrates produce the most fry per nest with an average of about 64,000 on sand and fine gravel.

Bluegill growth varies with population density. High population density limits growth while the opposite occurs with low density. Bluegill will reach 1- to 2-inches long on average in their first year of life. Most Bluegill in Iowa reach 3.5, 4.5, and 6-inches long in their second, third, and fourth year of life. Bluegills mature during the second year under suitable conditions, but slower growth will delay maturity to the third year. Bluegill reach up to 12-inches long and weigh up to 2 pounds, but most Bluegill caught by anglers are seldom over 8-inches. 

Bluegill are the most commonly caught, and one of the most highly sought after, species in Iowa. These fish are extremely important to anglers. Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.

Sources:

Harlan, J.R., E.B. Speaker, and J. Mayhew. 1987. Iowa fish and fishing. Iowa Conservation Commission, Des Moines, Iowa. 323pp.

Loan-Wilsey, A. K., C. L. Pierce, K. L. Kane, P. D. Brown and R. L. McNeely. 2005. The Iowa Aquatic Gap Analysis Project Final Report. Iowa Cooperative Fish and Wildlife Research Unit, Iowa State University, Ames

Illustration by Maynard Reece, from Iowa Fish and Fishing.