Rock Bass (Ambloplites rupestris)

Rock Bass (Ambloplites rupestris)

The rock bass is actually a member of the sunfish family and is not a true bass. Rock bass are fun to catch because they can be caught on many types of baits and lures, and they put up a decent fight on ultralight tackle. Rock bass are known to overpopulate small lakes, making population control measures necessary.

Identification

Although it looks like a cross between a bluegill and a black bass, the rock bass is actually a large and robust sunfish with a deep body; it is less compressed than most sunfish and is more similar to a black bass in shape. The back is raised, and the large head is narrow, rounded, and deep.

The mouth of the rock bass is large in comparison to other sunfish; the upper jaw reaches beyond the beginning of the eye but not to the back of the eye. It has two connected dorsal fins, five to six anal fin spines, and large eyes.


The rock bass is olive brown or bronze on the back and sides, with faint lines of tiny dark marks; the centers of the scales below the lateral line also have dark markings that form 11 or more rows and give the fish a striped appearance. In some rock bass, the coloring is lighter but consistent underneath, whereas others are silver, gray, or white on the bellies.

The ventral fins have pale circular spots, and all fins are usually darker at their margins, although the edges of the anal spines are white, the tips of the pectoral fins are clear, and the pelvic fins sometimes have a white edge. A distinguishing characteristic is the bluish-black blotch found on the tips of the gill covers.

Rock bass are frequently confused with the warmouth (Lepomis gulosus; see: warmouth). Warmouth have teeth on their tongue, whereas rock bass do not. There are also six spines in front of the anal fin of a rock bass, as opposed to the three spines in the warmouth. Rock bass may resemble the mud sunfish as well (see: Sunfish, Mud); rock bass have forked tails and rough scales, whereas mud sunfish have rounded tails and smooth scales.

Size/Age

The most common size for rock bass is about 8 ounces, although they have been known to reach 3 pounds. Often, rock bass in a particular lake will weigh around a pound, with a few fish exceeding 2 pounds. As with most sunfish, however, size is extremely variable, and rock bass living in streams are often stunted. The all-tackle record is a 3-pound Canadian fish.

Rock bass can reach a length of 12 to 14 inches but are usually less than 8 inches long. Although aquarium fish have lived for 18 years, those in the wild live 10 to 12 years on average.

Life history/Behavior

Rock bass are able to reproduce once they are 2 years old or 3 to 5 inches long; spawning occurs from midspring to early summer, when water temperatures range from 60° to 70°F. Males move into the shallows 3 to 4 days prior to the females’ arrival, to establish territories. They begin building round nests in gravelly or sandy areas near weedbeds or other protection, such as submerged tree trunks, using their pectoral, anal, and caudal fins to fan the gravel for the nests.

Spawning occurs during the day, usually in the morning. The females spawn at least twice, moving from nest to nest and laying from 3,000 to 11,000 eggs in total. The males guard the nests until the eggs hatch and the young swim away, and many males nest a second or even a third time.

Rock bass are a schooling fish and often cluster with other sunfish and smallmouth bass.

Food and feeding habits

Young rock bass feed on minute aquatic life when young, then on insects and crustaceans as they grow. Adults eat mostly crayfish, as well as minnows, insects, mollusks, and small fish. This diet varies with season and location. They can consume relatively large specimens because of their large mouths. Rock bass generally feed on the bottom but may occasionally feed near the surface.

Other Names

black perch, goggle-eye, red eye, rock sunfish, goggle-eye perch; French: crapet de roche.

Distribution

Native to the northeastern United States and southeastern Canada, rock bass range from southern Manitoba east to Ontario and Quebec, and southward through the Great Lakes region and the Mississippi Valley to the Gulf of Mexico and as far east as northern Alabama and northern Georgia. They have been introduced into other states, including some in the western United States.

Habitat

Rock bass prefer small to moderate streams with cool and clear water, abundant shelter, and considerable current; they are plentiful in shallow, weedy lakes and the outer edges of larger lakes, as well as in thousands of smaller lakes and ponds. Rock bass almost always hold over rocky bottoms (resulting in the name “rock” bass) where there is no silt. Young rock bass are frequently found in vegetation. Rock bass tend to frequent the same habitats as do smallmouth bass.

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