Illinois Natural History Survey - University of Illinois

Species Spotlight: The Common Stoneroller

The common stoneroller, Campostoma anomalum, is a dusky-colored minnow with scattered brown or black scales along its sides. This coloration helps it to blend in with its habitat--streams that have gravel, bedrock, or a mix of sand and gravel bottoms. The common stoneroller can be found throughout Illinois where these stream habitats occur. Stonerollers are lacking from the clay- or mud-bottom streams in the south-central part of the state. As a species, stonerollers are fairly intolerant of silt and disappear from degraded streams.

Common stoneroller (Campostoma anomalum). Photo by Michael Jeffords.

The common stoneroller ranges in size from 3 to 6.5 inches long and its snout is bluntly rounded and protrudes slightly beyond the mouth. The best diagnostic characteristic, unfortunately, requires the death of the fish. Common stonerollers differ from all other minnows in that their intestines are extremely long and spiral around their air bladders.

Stonerollers feed on algae, plant tissue, zooplankton, and the brown slime found on rocks and logs. The fish's lower jaw has a hardened, gristly edge that enables it to scrape surfaces for slime and scum.

During September and October the males develop tubercles. These tubercles are slightly hooked, whitish bumps that range from large near the head to small on the body and fins. They are used to help defend the fish's territory, for protection during digging in the gravel, and as an aid in grasping the spawning female. Shortly after spawning the tubercles are lost.

When the water temperature reaches 60deg. F the males begin nest construction. The nest site requires a gravel bottom and moderately shallow, clear water with a deeper pool nearby. The males have three distinct nest-building behaviors: picking, where the male takes a pebble in its mouth, brings it to the edge of the nest pit, and then releases it; digging, where the male pushes its head down into the nest pit and swims into the gravel with a writhing movement that loosens the gravel; and pushing, where the male places its snout against a stone and swims into it. Stoneroller nests are irregular in outline, are several inches across, and are often used by several males.

While the males are diligently engaged in nest-building, females "hang out" in schools 5 to 30 feet away from the nest-building area. When a female is ready to spawn she will move into the nest area. Her eggs will become lodged in the gravel, are fertilized by a male, and are then abandoned. Fertilized eggs hatch within 72 hours.

Susan Post, Center for Economic Entomology


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