Brook Silverside

Characteristics

A very slender, elongate and translucent fish. Its head is flattened with a beak-like snout and a lower jaw that slightly projects toward the front. Upper and lower jaws have tiny, needle-like teeth. The long, sickle-shaped anal fin has one spine and 20 to 26 rays. Two dorsal fins are on the posterior half of the back. The first dorsal has 4 spines, and the second has one spine and 5 rays. Scales are small and cycloid with 75 to 84 scales along the lateral line. General body color is pale green. The dorsal scales are outlined with black specks, its sides are silvery with a bright silver horizontal stripe, and the belly is silvery-white. The fins are plain, except for a spinous dorsal fin and pigmentation near the tip. Adults usually average 2- to 4-inches long.

Distribution

Almost exclusively in northeast Iowa; found throughout the Mississippi River, but most abundant in Pools 9-14. It has also been collected in the Cedar and Maquoketa River drainages. Despite pre-1900 reports, recent collections have failed to document this fish species in central Iowa streams.

Foods

Aquatic and terrestrial insects.

State Record

State Records are not documented for non-game species.

Expert Tip

This fish is often a food item for predatory fish, so in waters where it exists,"match the hatch" and try lures that resemble the Brook Silverside.

Details

The Brook Silverside prefers clear, warm backwaters of streams, lakes, bayous, oxbows and borrow pits with bottoms made of clean sand, gravel or organic muck. It is occasionally found in areas with sparse, but never dense, vegetation. In the Ozarks and forested portions of the upper Midwest, the Brook Silverside is most often found in warm, permanent pools of small headwater creeks and overflow pools of larger streams with little current. Several investigators report that the Brook Silverside lives in small streams with considerable current. In the clear waters of lakes and newly built reservoirs it prefers coves or shorelines where it quickly becomes abundant. It is sensitive to high turbidity and siltation.

Brook Silversides seldom venture below the upper 3 feet of water, and spend most of their time within inches of the surface. The up-turned mouth and flattened head are adapted to a surface-dwelling life. Young fish feed in open water on cladocera, copepods and other small crustaceans, As they become older, they move toward shore and eat both aquatic and terrestrial insects. It is very active in the daylight and moonlit nights, but lies motionless near the surface on dark nights.

Spawning takes place over shallow, gravel bottoms or sites with submerged vegetation, from late May to early August. The eggs are extruded singly as a spawning pair moves at an angle from the surface to the bottom. Each egg has an adhesive filament that attaches to the first item it contacts. At 77 degrees, the eggs hatch in about 8 days. The Brook Silverside matures, spawns and dies by the end of its second summer of life.

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

Sources:

Harlan, J.R., E.B. Speaker, and J. Mayhew. 1987. Iowa fish and fishing. Iowa Conservation Commission, Des Moines, Iowa. 323pp.

Loan-Wilsey, A. K., C. L. Pierce, K. L. Kane, P. D. Brown and R. L. McNeely. 2005. The Iowa Aquatic Gap Analysis Project Final Report. Iowa Cooperative Fish and Wildlife Research Unit, Iowa State University, Ames.

Illustration by Maynard Reece, from Iowa Fish and Fishing.