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The Rock Bass is olive colored with brassy reflections and dark mottlings along the sides. It has a whitish breast and belly. Six spines are in anal fin and 12 in the dorsal. It seldom exceed 10 inches.
Northeastern interior streams; rarely in the upper part of the Des Moines and Mississippi Rivers and 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.
Occurrence of this species is limited in Iowa to the clearer, rocky habitats of the interior streams, mainly streams in the northeast part of the state. They are common in these reaches. Rock Bass are rarely found in the upper parts of the Des Moines and Mississippi rivers. Occasionally it is found in the large, natural lakes.
The Rock Bass is 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 pronounced 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.
This fish lives in the same environment as Smallmouth Bass, and their food habits are similar, except smallmouth eat more fish. Young Rock Bass eat zooplankton as their primary forage, but as they grow larger there is a selection of more aquatic insects in the diet which is supplemented with minnows and other small fish.
The Rock Bass is mainly a sedentary and secretive fish spending much of its activity passively hiding in the shadows of underwater structures.
Spawning coincides with that of Smallmouth Bass. Nest building by the male starts when the water temperature is 65 to 75 degrees F, 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 in length after three years. Rock Bass have lived 13 years in nature and weighed 1 1/2 pounds, but most Rock Bass in Iowa seldom exceed 10 inches. The Iowa record for Rock Bass is 1 pound, 8 ounces, and was caught in 1973.