Smallmouth Bass

Characteristics

A slender, streamlined-shaped fish with a moderately large mouth, where the upper jaw reaches about to the rear margin of the eye in adults. Spiny and soft parts of the dorsal fin are broadly connected with only a shallow notch between the lobes. The body is golden green on the sides and back with faint wavy olive blotches evenly spaced along the sides. Five olive-green bars radiate backward from the eye, and one forward to the end of the snout. The tail fin in young smallmouth is tri-colored with a black vertical bar separating the yellowish fin base. Pyloric caeca are not forked in contrast to forked pyloric caeca in the closely related Largemouth Bass.

Distribution

Northeastern 2/3 of Iowa in clear rivers, streams and some lakes; most abundant in northeast Iowa.

Foods

Fish, crustaceans, larger insects

State Record

7 pounds, 12 ounces - West Okoboji Lake, Dickinson County, September 1990 - Rick Gray, Dickinson, Iowa

Expert Tip

Use light spinning gear with crayfish colored crankbaits for hot smallmouth action.

Details

Smallmouth Bass are omnivorous in the food they eat. In the larger cool, clear interior streams of northeast Iowa, Smallmouth Bass is the dominant predator, eating mostly fish, crustaceans and larger aquatic and terrestrial insects. Food habit studies show that forage fish were in 40 percent of the stomach samples, crayfish in 30 percent and insects in 20 percent. Where crayfish are abundant, they often make up over two-thirds of the food. Newly hatched smallmouth eat copepods and cladocerans, but start to eat insects when about one-half inch long. When fingerling Smallmouth Bass are 1 1/2 inches long, insects and small fish make up the bulk of their diet.

Smallmouth Bass spawn in Iowa in early May as water temperatures exceed 60 degrees. To prepare for spawning, parent spawners move up larger streams, eventually reaching small tributaries where the actual spawning happens. Male fish build a saucer-shaped nest on the gravel, coarse sand or rock bottom by sweeping its tail over the substrate. The 14- to 25-inch diameter nest is found in quiet water near the shoreline downstream from a boulder or other natural structure that deflects and slows the current.

The ripe male bass selects a gravid female after the nest is built and nudges her toward the nest in a series of aggressive body contacts and bites. If the female refuses the nest, the male becomes more aggressive until the female is physically driven over the depression. Both fish lie side by side, facing the same direction during the release of eggs as the female vibrates her body by muscle action. The male releases milt for fertilization as the eggs are deposited. The female leaves the nest after spawning, but may return later to the same nest or another if she has hidden egg development. Male fish usually ripen again after a short time. Male fish protect the nest from predators and fan the eggs free of silt until the sac fry emerge in 3 to 5 days, depending on water temperature. Re-nesting is common for smallmouth, mainly when early nests are destroyed by natural events such as a flood.

The number of eggs a female Smallmouth Bass lays varies greatly depending on body size. Average is 7,000 to 8,000 eggs per pound of body weight. Newly hatched sac fry swim over the nest in a school for about 6 to 15 days, moving sluggishly until all the nourishment in the yolk sac is eaten. The young fry are about one-half inch long when the yolk sac is absorbed, and they leave the nest to eat small crustaceans and copepods.

Smallmouth Bass growth varies with the amount of food eaten and water temperature. Most Smallmouth Bass in Iowa reach 3- to 5-inches by the first autumn, 6- to 7-inches in the second year, and 9- to 10-inches the third year. Smallmouth sexually mature in the second or third year of life, but where food is scarce or water is relatively cool in all seasons, maturation may not occur until the third or fourth year. Maximum weights of 6- or 7-pounds have been reported in Iowa, but fish over 3- to 4-pounds are trophy sized.

Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.