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.