Fish
Cutlip Minnow
Exoglossum maxillingua · also called cutlip minnows
In a clear, gravelly headwater stream, a cutlip minnow approaches another fish and uses its unusual three-lobed jaw to nip a small piece of fin tissue, a specialised feeding habit that sets this otherwise plain-looking minnow apart from nearly all its relatives.
Overview
The cutlip minnow, Exoglossum maxillingua, is a small fish native to headwater streams across a range spanning the northeastern and mid-Atlantic United States. Its unusual three-lobed jaw, specialised fin-nipping feeding behaviour, and stone-mound nest-building make it one of the more physically and behaviourally distinctive minnows found in eastern North American streams.
A jaw built for something other than grazing
While many minnows use specialised mouths to scrape algae, the cutlip minnow’s odd three-lobed jaw serves an entirely different purpose, nipping pieces from other fish rather than feeding on plant material at all.
Status
Least Concern — widespread and stable across suitable clear, gravelly headwater stream habitat throughout the northeastern and mid-Atlantic United States.
Cutlip Minnow: common questions
Why does the cutlip minnow nip other fish?
This species has a distinctive three-lobed lower jaw adapted partly for nipping fins, scales, and other soft tissue from other fish, a specialised feeding behaviour that supplements its diet of fish eggs and small invertebrates, and one that sets it apart from most other North American minnow species with more typical feeding habits.
How does a male cutlip minnow build its nest?
A breeding male of this species constructs a nest by carrying and piling small stones into a mound on the streambed, then defends the completed nest and any resulting eggs against intruders, a nest-building and guarding strategy shared with certain other minnow species.
How can you identify a cutlip minnow?
This species has a relatively plain, olive-brown body without particularly bold markings, making its unusual three-lobed lower jaw the most distinctive and reliable feature for identification, since the body colouration alone does not stand out strongly from several other similarly plain minnow species.
What kind of stream does the cutlip minnow prefer?
This species favours clear, gravelly, moderately flowing headwater streams, generally avoiding heavily silted or slow-moving water, a habitat preference shared with several other minnow species adapted to clean, well-oxygenated headwater conditions.