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Brook Silverside is a very slender, elongate and translucent fish. The head is flattened with a beak-like snout and a lower jaw that slightly projects toward the front. Upper and lower jaws have minute, needle like teeth. The long, sickle-shaped anal fin has one spine and 20 to 26 rays. Two dorsal fins are located 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, the 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 in length, and these fish are always found in the upper three feet of water.
The Brook Silverside is commonly collected in pools 9 through 13 of the Mississippi River and is occasionally observed in downstream pools. It also has been collected in the Maquoketa and Cedar rivers. Recent collections in central Iowa rivers have not documented this species. Habitat preference for Brook Silversides is clear, warm waters having little current.
Aquatic and terrestrial insects.
State Records are not documented for non-species game.
This fish is often a forage (food) item for predatory fish, so in waters where it exists, "match the hatch" and try lures that resemble the Brook Silverside.
The Brook Silverside is found almost exclusively in the northeastern Iowa. It is found throughout the Mississippi River, though is most abundant in Pools 9-14. The Brook Silverside 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.
The Brook Silverside prefers clear, warm backwaters of streams, lakes, bayous, oxbows and borrow bits with bottoms composed of clean sand, gravel or organic muck. It is occasionally associated with sparse but never dense vegetation. In the Ozarks and forested portions of the upper Midwest, the Brook Silverside is most often found warm, permanent pools of small headwater creeks and overflow pools of larger streams with little current. However several investigators report that the Brook Silverside inhabits small streams with considerable current. In the clear waters of lakes and newly constructed reservoirs it prefers coves or shorelines where it quickly becomes abundant. The Brook Silverside is sensitive to high turbidity and siltation.
Brook Silversides seldom venture below the upper 3 feet of water, and mos of their time is spent within inches of the surface. The up-turned mouth and flattened head are adapted to a surface-dwelling life. Young fish forage in open water on cladocera, copepods and other small crustaceans, As they become older, the fish move toward shore and feed on a diet of both aquatic and terrestrial insects. The fish 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 a temperature of 77 degrees F 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.
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.