Smallmouth Bass (Micropterus dolomieui)

Smallmouth Bass (Micropterus dolomieui)

The smallmouth bass is the second largest member of the Centrarchidae family of sunfish and a North American original. To anglers, it is one of the most impressive of all freshwater fish and is coveted for its fighting ability.

The smallmouth is not actually a bass but a sunfish, and its mouth is only small in comparison to that of some relatives. It is naturally a fish of both clear rivers and lakes and has been widely introduced to other waters outside its original range.

Smallmouth bass that reside in small to intermediate streams do not grow as large, on average, as those from lakes or reservoirs, although fish from big rivers, and especially those with tailwater fisheries, can attain large sizes. River smallmouth bass are even spunkier than their lake-dwelling brethren, however, and tend to be more streamlined and to lack drooping bellies.

The smallmouth bass is occasionally confused with the largemouth where they both occur, and also with the spotted bass and the redeye bass. They have been known to hybridize with spotted bass. Two subspecies are often recognized: the northern smallmouth, Micropterus dolomieui dolomieui, and the Neosho smallmouth, M. d. velox.


The smallmouth bass has a robust, slightly laterally compressed and elongate body; a protruding lower jaw; red eyes; and a broad and slightly forked tail. Its pelvic fins sit forward on the body below the pectoral fins; a single spine is found on each pelvic fin and on the front of the anal fin.

The two dorsal fins are joined or notched; the front one is spiny and the second one has one spine followed by soft rays. Its color varies from brown, golden brown, and olive to green on the back, becoming lighter to golden on the sides and white on the belly. Young fish have more distinct vertical bars or rows of spots on their sides, and the caudal, or tail, fins are orange at the base, followed by black and then white outer edges.

The smallmouth is easily distinguished from the largemouth by its clearly connected dorsal fins, the scales on the base portion of the soft-rayed second dorsal fin, and the upper jawbone, which extends only to about the middle of the eye. The coloration is also distinctive, being usually more brownish in the smallmouth and more greenish in the largemouth.


The average life span of the smallmouth bass is 5 to 6 years, although it can live for 15 years. Most smallmouth bass encountered by anglers weigh between 1 and 1.5 pounds and are from 9 to 13 inches long; fish exceeding 3 pounds are considered fairly large but not uncommon. The largest smallmouth known is the Tennessee state record, a fish that weighed 11 pounds, 15 ounces, when caught from Dale Hollow Lake in 1955.

The Neosho subspecies, which is more slender than the smallmouth, occurs in the Neosho River and tributaries of the Arkansas River in Missouri, Kansas, Arkansas, and Oklahoma.

Life history/Behavior

Smallmouth bass spawn in the spring (or the early summer in most northern waters), when the water temperature is between 60° and 65°F. The male builds a nest in water that ranges from 1 to 12 feet deep, depending on the environment. The nest site is often over a gravel or rock bottom but may be over a sandy bottom in lakes, and it is usually near the protection of a log or a boulder.

Older bass prefer rocky, shallow areas of lakes and rivers and retreat to deeper areas when water temperatures are high. They tend to seek cover and avoid the light and generally do not inhabit the same types of dense, weedy, or wooded cover that largemouth bass prefer. They hide in deep water, behind rocks and boulders, and around underwater debris and crevices, preferring water temperatures between 66° and 72°F.


These highly carnivorous and predatory fish will eat whatever is available, but they have a clear preference for crayfish and small fish. In lakes, this includes small bass, panfish, perch, and assorted fingerling-size minnows in lakes. In rivers, it includes minnows, crayfish, hellgrammites, nymph larvae, and leeches.

Other Names

black bass, smallmouth, bronzeback, brown bass, brownie, smallie, redeye; French: achigan à petite bouche; German: schwarzbarsch; Japanese: kokuchibasu.


The smallmouth bass is endemic only to North America, and its original range was from the Great Lakes and the St. Lawrence River drainages in Canada south to northern Georgia, west to eastern Oklahoma, and north to Minnesota.

It has since been widely spread within and beyond that range, across southern Canada west to British Columbia and east to the Maritimes, west to the Pacific coast states, and into the south-western United States. It has also been introduced to Hawaii, Asia, Europe, and Africa.


Smallmouth bass prefer clear, quiet waters with gravel, rubble, or rocky bottoms. They live in midsize, gentle streams that have deep pools and abundant shade or in fairly deep, clear lakes and reservoirs with rocky shoals. Although they are fairly adaptable, they are seldom found in murky water and avoid swift current.

In the typical river, smallmouth bass predominate in the cool middle section where there are large pools between riffles, whereas trout occupy the swifter and colder upper section. In stillwaters, smallmouth bass may occupy lakes, reservoirs, or ponds if these waters are large and deep enough to have thermal stratification, and they are usually located deeper than largemouth bass once the surface layer warms in the spring or early summer.