The little silvery fish darting under a footbridge in a shallow stream is very often a Creek Chub (Semotilus atromaculatus). It is one of the most widespread minnows in eastern North America, and the males are surprising stream engineers in spring.
What it looks like
Usually 8 to 15 cm long, though big ones can reach 25 cm. The body is slender and silvery-olive with a dark stripe running along the side and a small black spot at the base of the tail fin. There is a tiny dark spot at the front of the dorsal fin too. In spring, breeding males turn rosy and develop hard bumps, called tubercles, on the head used in fights.
When and where
- Season: Active year-round, most visible and active spring through summer.
- Habitat: Small creeks, brooks, and headwater streams with gravel or sand bottoms and steady flow.
- Best time: Daytime in clear, shallow riffles and pools where you can watch them from the bank.
Pebble nests built by mouth
In spring, the male builds a nest by carrying gravel one stone at a time in his mouth, piling pebbles into a long ridge or mound on the streambed. The structure can hold thousands of eggs and can take real effort to assemble. He guards it fiercely until the eggs hatch. Other minnow species often slip in to spawn over these nests too, quietly using the chub's hard work.
Spot one this weekend
Creek Chubs are Common. Stand quietly on a bank above a shallow, clear creek and watch the gravel for darting shapes and the telltale dark side stripe. In late spring, look for low ridges of clean, freshly moved pebbles, a sure sign a male has been nest building.