Smallmouth Bass

Micropterus dolomieu

Type: Freshwater, Bony Fish

Smallmouth Bass

Physical Characteristics

The body is slender and streamlined with a brownish/bronze to olive-green hue. It features 8 to 15 characteristic vertical bars on the sides. The mouth is large, but the upper jaw does not extend past the rear edge of the eye when closed. They have two dorsal fins that are broadly connected, looking like one.

Habitat & Distribution

Found in clear, cool-to-warm flowing streams and rivers with gravelly or rocky bottoms, as well as clear lakes with rocky shoals and limited vegetation. Native to the east-central North American basins of the Mississippi, Saint Lawrence-Great Lakes, and Hudson Bay.

Size & Weight

Typically ranges from 12 to 20 inches in length and 1 to 4 pounds. The world record is 11 pounds 15 ounces and 27 inches.

Similar Looking Species

Largemouth Bass (Micropterus salmoides) – distinguished by a larger mouth where the jaw extends past the eye and a horizontal lateral stripe instead of vertical bars. Spotted Bass (Micropterus punctulatus) – has rows of small spots on the lower side and a distinct rough patch of teeth on the tongue.

Ecological Role

They are top-tier apex predators in many of their native river ecosystems, helping to regulate populations of smaller fish and crayfish.

Diet

Opportunistic carnivores. Juveniles eat plankton and tiny aquatic insects; adults primarily consume crayfish, smaller fish, and occasionally amphibians or large insects.

Behavior

Known for being highly territorial and aggressive. They are often solitary but can be found in small groups near underwater structure. They are mostly diurnal, being most active during early morning and late evening.

Reproduction

Spawning occurs in spring when water temperatures reach 60°F (15.5°C). The male builds a nest in gravel or sand, guards the eggs, and protects the fry for several weeks after hatching.

Conservation Status

Least Concern (IUCN). Populations are generally stable or increasing due to widespread introductions beyond their native range.

Identification Tips

Look for the vertical bars along the sides, red or orange eyes in some individuals, and check the jaw length; if the mouth ends before or even with the eye, it is likely a smallmouth.

Interesting Facts

Also known as the 'bronzeback' because of its color. Unlike many other bass species, they are highly sensitive to pollution and are often used as an indicator species for clean water health.

Identified on: 4/27/2026

Mode: Standard