Smallmouth Bass

Micropterus dolomieu

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Smallmouth bass side view photo with black background
Smallmouth bass, Micropterus dolomieu
Lance Merry
Other Common Name
Brown Bass; Brownie; Bronzeback
Family

Centrarchidae (sunfishes) in the order Perciformes (perch-like fishes)

Description

The smallmouth bass is a large, elongated fish with a moderately large mouth. The cheek scales are much smaller than the rest of the body scales. The back and sides are greenish brown, with faint dark mottling and bars; the belly is whitish, overlain with dusky pigment.  There is no dark horizontal stripe, and it lacks rows of dark spots. In adults, the upper jaw reaches to about the rear margin of the eye. The tongue usually has a rough patch. The two dorsal fins are connected.

Similar species: The smallmouth bass is most closely related to the largemouth and spotted basses.

Key Identifiers

 

  • In adults, the upper jaw extends to about the rear margin of the eye; it does not extend beyond the back of the eye (in largemouth bass, the upper jaw extends far behind the back of the eye)
  • The 2 dorsal fins are connected
  • Side is plain, with a series of separate vertical bars
  • Very small cheek scales
Size

Total length: 10 to 20 inches; weight 1/2 to 4 pounds; maximum about 22 inches long and 6 pounds.

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Smallmouth bass adult side view photo with black background
Smallmouth Bass
Smallmouth bass, Micropterus dolomieu, adult

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Smallmouth bass juvenile side view photo with black background
Smallmouth Bass Juvenile
Smallmouth bass, Micropterus dolomieu, juvenile

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Smallmouth bass juvenile side view photo with black background
Smallmouth Bass Juvenile
Smallmouth bass, Micropterus dolomieu, juvenile

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Smallmouth bass being held up by a person
Smallmouth Bass
In smallmouth bass, the two dorsal fins are connected, the cheek scales are very small, and the upper jaw does not extend beyond the back of the eye.

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Three captured fish lying on a surface, left to right: largemouth bass, spotted bass, and smallmouth bass
Missouri's 3 Species of Black Basses: Largemouth, Spotted, and Smallmouth
From left to right: largemouth, spotted, and smallmouth bass. They are in the same genus, Micropterus, the "black basses."

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Image of a smallmouth bass
Smallmouth Bass

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smallmouth bass
Smallmouth Bass
Habitat and conservation

Found predominantly in cool, clear Ozark streams and large reservoirs in the Ozarks. Found sparingly in the upper Mississippi River and its principal prairie tributaries that have clear water and permanent flow. Thrives in clear streams, with silt-free rock or gravel bottoms, near riffles but not in the main current. Although mostly found in streams in Missouri, it can be found in natural lakes and ponds in the northern parts of its North American range. Most active at dawn and dusk.

Foods

Carnivorous, feeding on fish, crayfish, and large aquatic insects. When actively foraging for minnows and other prey, smallmouth bass commonly prowl the shoreline in quite shallow water.

The first foods of smallmouth fry include midge larvae and microcrustaceans. Fry less than an inch long are already capable of eating small fish.

An interesting habit of smallmouth bass is to follow a large turtle or sucker as it digs or roots in the bottom, pouncing on any insects or crayfish that are disturbed by this activity.

image of Smallmouth Bass distribution map
Distribution in Missouri

Predominantly in cool, clear Ozark streams and large reservoirs in the Ozarks. Sparingly in the upper Mississippi River and most of its principal prairie tributaries.

Status

This is the most sought-after sport fish in the clear, cool streams of the central Ozarks. In recent years it has become increasingly abundant and important in the sport fishery of Table Rock Reservoir and Stockton Lake.

Populations have declined in the Moreau River drainage partly because of hybridization with an introduced population of the closely related spotted bass.

Life cycle

Smallmouth bass spawn from early or mid-April (when the water temperature exceeds 60 F) and continues well into June or even July. Peak spawning activity is in May. Smallmouth bass spawn in quiet water near shore, or downstream from a boulder or other obstruction that breaks the force of the current. Typically, nests are located where there is no perceptible current, not far from cover or deeper water to which the male retreats when frightened.

The male smallmouth fans out a nest with powerful sweeping motions of his tail fin, in typical sunfish fashion. The nest is swept clean of silt, sand, and fine gravel, leaving a saucer-shaped depression with a diameter about twice the length of the male. The nest is floored by coarse gravel and rock.

Females enter the nest only to spawn. The male does not assume special breeding colors, and most of the time the sexes are difficult to distinguish. However, when entering the nest, the female develops a strongly barred and blotched pattern, while the male retains a uniform coloration. Spawning occurs during a period of 20 or 30 minutes, until the full complement of eggs is deposited. Sometimes more than one female enters the nest at the same time, and a single nest may contain the eggs of several females.

Nests contain about 2,500 eggs on average, but sometimes 10,000 eggs are present. They hatch in 2 or 3 days. The fry remain at the nest and continue their growth and development for about 12 more days; soon after, they disperse.The male guards the nest and fry until they are gone.

As many as 80,000 bass fry are produced in a single mile of Ozark stream, but these may be reduced to less than 100 by early September of the first year of life. They are most vulnerable when they are small; as they grow larger, their potential predators become more limited. Individuals can live up to about 10 to 12 years.

Human connections

A popular sport fish of the Ozarks. The most effective live baits include minnows, crayfish, and hellgrammites. Spinning and casting with the same types of lures used for taking largemouth bass also work. Some people consider fly fishing to be the ultimate sporting method for catching "brownies."

One of the craft breweries based in Missouri's Ozarks named its "Bronzeback" beer to celebrate this favorite sport fish.

Ecosystem connections

In the Ozarks, the smallmouth bass is the dominant species of large, predatory fish in most streams. It is the ecological replacement, or counterpart, for the spotted bass and the largemouth bass in the clear, cool, permanent-flowing streams of the Ozarks.

The nests of smallmouth bass are centers of activity for other fishes. Longear sunfish, for example, commonly gather around smallmouth nests and rush in to feed greedily on eggs or fry if the guardian male smallmouth is distracted or frightened away.

Shortly after hatching, orangethroat darter fry sometimes inhabit the nests of smallmouth bass. Many bass nests literally swarm with darters. It is believed that the young orangethroats benefit from the protection of the male bass guarding its nest; the full-grown bass will not feed on such "small fry." There may also be more of the preferred prey for the orangethroat fry in these locations, too.