Western blacknose dace

Rhinichthys obtusus

Order: Cypriniformes

Family: Cyprinidae

Genus: Rhinichthys

The Western blacknose dace is a small, bottom-dwelling minnow recognized by its dark lateral stripe, short snout, and slightly subterminal mouth well-suited to foraging along the substrate. Adults typically grow 5 to 8 centimetres long, with some individuals reaching up to 10 centimetres. Their bodies are torpedo-shaped and often speckled with darker pigments above the stripe, blending well with gravel or rocky streambeds. Males become more vibrantly coloured during the breeding season, developing reddish tones around the fins and lower body.

This species is well adapted to cool, flowing water and can often be found darting among cobbles and detritus in shallow riffles, where it seeks both food and cover.

Conservation Status: IUCN

Distribution

Found across central and eastern North America, including the Great Lakes basin, southern Ontario, the Ohio and Mississippi River systems, and upland Appalachian streams. It is one of the most common minnows in many Canadian and U.S. headwater habitats.

Habitat

Prefers clear, cool, well-oxygenated streams with gravel or rocky substrates and moderate to fast current. Frequently occupies riffles, undercut banks, and edge habitats with aquatic vegetation. It requires unpolluted water and natural stream structures for breeding and shelter.

Diet

Omnivorous. Eats aquatic insect larvae, small crustaceans, algae, and organic detritus. Feeds primarily near the stream bottom, using its sensitive mouthparts to pick food from between gravel and cobble.

Reproduction

Spawning occurs in late spring to early summer, when males establish small territories in shallow gravel areas. Females lay eggs in these spots, often among the pebbles. Fertilized eggs are left unguarded and develop in the substrate. Young fish hatch within days and begin feeding almost immediately.

Adaptation

Counter-shaded body camouflages them in rocky stream environments
Small size and darting movement help evade predators in shallow water
Strong rheotactic behaviour (orientation to flow) aids in station-holding in currents
Subterminal mouth is adapted for foraging along the stream bottom

Threats to Survival

While currently secure, they are vulnerable to:

Stream pollution from agricultural runoff or urban stormwater
Excessive sedimentation, which can smother eggs and reduce feeding efficiency
Habitat fragmentation from culverts and dams
Warming water temperatures and reduced summer flows from climate change