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A stout, heavy-bodied sunfish with a large mouth, which extends beyond mid-eye when the mouth is closed. The spiny dorsal fin and soft dorsal fin are broadly connected, but without a notch. The dorsal fin is much longer and more noticeable than the anal fin. Six anal fin spines and 12 dorsal fin spines distinguish this fish from all other sunfishes. The body is olive with brassy reflections and dark mottlings along the sides. The breast and belly are whitish, and the lower side has spots that form horizontal lines. There is brown mottling and faint banding on the anal, dorsal and tail fins. The pectoral fins are rounded, set low and are amber in color.
Limited to the clearer, rocky habitats of the interior streams in northeast Iowa. Rarely found in the upper parts of the Des Moines and Mississippi rivers. Occasionally found in the large, natural lakes.
aquatic insects, minnows and other small fish
1 pounds, 8 ounces - Mississippi River, Dubuque County, June 1973 - Jim Driscoll, Dubuque, Iowa
True to their name, the Rock Bass can be caught in streams by fishing close to the rocks near the current.
The Rock Bass is mainly a sedentary and inactive fish, spending much of its activity hiding in the shadows of underwater structures.
Spawning matches that of Smallmouth Bass. Spawning starts when the water temperature is 65 to 75 degrees, usually in May and June. Males build nests over gravel and sand bottoms where the females lay several thousand eggs. Females have an average of 5,000 eggs, but one or several fish may deposit part or all of their eggs in a single nest. After hatching, the young fish are found only in quiet water areas protected from waves and strong current. Rock bass grow 1 1/2- to 2-inches the first year and reach 5- to 7-inches long after three years. Rock Bass have lived 13 years in nature and weighed 1 1/2 pounds, but most seldom exceed 10-inches.
Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.