Micropterus dolomieui
Smallmouth Bass

Smallmouth Bass

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The natural history of the northwoods



  • Micropterus, from the Greek, "small fin"
  • dolomieui, in honor of Dieudonné de Dolomieu, a French mineralogist
  • Common name from the size of its mouth relative to that of its cousin, the Largemouth Bass. (In and of itself the Smallmouth doesn't have a particularly small mouth.)
  • Other common names include: Black Bass, Bronzeback, Brown Bass, Browny, Green Bass, Green Trout, Jumper, Mountain Trout, Northern Smallmouth Bass, Oswego Bass, Redeye Bass, River Bass, Smallie, Smallmouth Black Bass, White Trout


  • Kingdom Animalia
    • Phylum Chordata, animals with a spinal chord
    • Subphylum Vertebrata, animals with a backbone
      • Superclass Osteichthyes, bony fishes
      • Class Actinopterygii, ray-finned and spiny rayed fishes
      • Subclass Neopterygii
      • Infraclass Teleostei
        • Superorder Acanthopterygii,
        • Order Perciformes, perch-like fishes
        • Suborder Percoidei
          • Family Centrarchidae, sunfish
            • Genus Micropterus, black basses, largemouth basses


  • A slender, streamlined perch
  • Length 15"-20"
  • Weight 1½-5 lbs
  • Coloration
    • brown, golden-brown, through olive to green on back
    • sides lighter, with faint, evenly spaced, wavy olive blotches
    • cream to milk-white underside
    • broad lateral line
    • 5 olive-green bars radiate back from the red eye and 1 radiates forward to the end of the snout.
  • Body
    • spiny and soft portions of dorsal fin broadly connected, with only a shallow notch between lobes.
    • tail fin in young distinctly tri-colored, with a black vertical bar separating the yellowish fin base.
  • Head
    • moderately large mouth, where the upper jaw reaches to near the rear margin of the eye in adults


  • Distinguished from its largemouth cousin by:
    • its mouth, though hardly small, is no match for the largemouth's; the maxilla extends rearward only about even with the pupil.
    • notch between the spiny and soft parts of the dorsal less pronounced
    • irregular vertical bars or a continuous shading of dark brown above to a gray or cream below.


  • Southern Quebec and Ontario, New York, west to Minnesota; south in Mississippi drainage to northern Arkansas and Alabama. Widely introduced.
  • The Boundary Waters are at the northern edge of its natural range.
  • During late 19th Century valued nearly as highly as trout and salmon and transplanted to new watersheds with great enthusiasm but few records. Probably not native to Minnesota lakes that provide some of the best smallmouth fishing, including the large border lakes of the BWCA.


  • Primarily an inhabitant of swift flowing, less turbid waters in rivers and smaller streams, usually near rocks. (Prefers gravel under 1" in diameter to build nests and spawn). Does well in northern lakes.
  • Water temperatures must reach the low 60 ºs for spawning, one reason many coldwater streams hold trout rather than bass.
  • Needs a great amount of dissolved oxygen and, in streams, a dependable streamflow and modest current.
  • Retreats to pools, undercut banks, or deep water to avoid bright daylight. Most active in early morning and evening. In winter, they gather near bottom and feed little until spring and water temperatures rise to about 47 º F.


  • Crayfish are favored prey, though they also feed heavily on fish. Crustaceans and larger insects also figure in diet.
  • Newly hatched young consume copepods and cladocerans but begin to forage on insects when about ½" long. By the time fingerlings are 1½" in length, insects and small fish comprise bulk of diet.


  • U.S. Record: 11 lbs 15oz, from Dale Hollow Lake, Kentucky, 1955
  • Minnesota Record: 8 lbs 0oz, from West Battle Lake (Otter Tail County).


  • Highly regarded as a feisty sport fish. It is usually associated with a rocky stream or lake environment where its favorite food, crayfish, is abundant.


  • Spawns in spring, in gravelly shallows of lakes or large, gentle eddies in streams, when water temperatures reach 62º-64º F.
  • Male assembles a saucer-shaped nest, 14"-25" in diameter, on the gravel, coarse sand or rock bottom by sweeping its tail over the substrate. The female lays 2,000 to 10,000 eggs and then heads for deep water.
  • Male protects the nest from predators of his own and other species and fans the eggs free of silt until the sac fry emerge in 3-5 days, depending on water temperature. Re-nesting is quite common, particularly when early nests are destroyed by flood or similar natural disaster.
  • Newly hatched sac fry swim over the nest in a school for about 6-15 days, moving sluggishly until all the nourishment in the yolk sac is consumed. The young fry are about one-half inch long when the yolk sac is absorbed, and they leave the nest to feed on small crustaceans and copepods.
  • As with the Largemouth, there is no relationship between the number of spawning fish and the success of the spawn. The strength of the year class depends solely on water conditions - in particular, the absence of a sudden cold snap or muddy floodwaters that can kill eggs and fry.
  • Sexually mature in the second or third year, but where food is scarce or water relatively cool in all seasons, may not occur until third or fourth year.


  • Interestingly enough, the generic name for our freshwater bass, Micropterus, meaning "small fin", is a misnomer. The speciman from which the genus was named had a damaged fin which gave the appearance of a small fin behind the dorsal. This characteristic, needless to say, is not shared by the other members of the genus. Ah, taxonomy is such an exacting science...


Boreal border

Last updated on 13 November 1999