Carp, Sucker or Buffalo? Look at the Mouth

Large, deep-bodied, bottom-oriented fish in murky water all get called carp. Three unrelated groups are involved, and one look at the mouth separates them.

Barbels first

Common carp have two pairs of fleshy barbels at the corners of the upper jaw — one long pair, one short. Nothing else in this group has them.

Suckers and buffalo have none. Their mouths are fleshy and lipped, positioned for feeding off the bottom, with no whiskers at all.

Catfish have four pairs and are unmistakable, and no scales, which settles it instantly.

That single check sorts carp from the native suckers, which is the confusion that matters most because the two are treated very differently by regulation.

The dorsal fin

Carp and buffalo both have a long dorsal fin running much of the length of the back. Redhorse and most other suckers have a short one.

So a large scaled fish with a long dorsal and no barbels is a buffalo; with barbels, it is a carp. That pair of checks handles almost every case.

Mouth position

Suckers are named for it. A redhorse or white sucker has its mouth on the underside of the head, pointing down, built to work along the bottom.

Buffalo have a more forward-facing mouth, which is part of why they are mistaken for carp. Carp mouths are terminal and protrusible, extending forward into a tube when feeding.

Why the distinction matters

Common carp are introduced and are managed as invasive in much of North America, with no size limits and in some places a prohibition on returning them alive.

Buffalo and redhorse are native. Some are common; several redhorse species are of conservation concern, and bigmouth buffalo have recently been shown to be extraordinarily long-lived — individuals over a hundred years old have been aged, which changes how populations should be managed.

Killing a native sucker in the belief it is an invasive carp is therefore a real and common error, and the barbel check prevents it.

Grass carp and silver carp

Two further introduced species that are not common carp.

Grass carp have no barbels, which breaks the rule above, and are distinguished by a shorter dorsal fin and a more torpedo-shaped body. They are stocked for weed control in some waters and are frequently required to be sterile triploids.

Silver carp are the ones that jump. Deeply keeled belly, very small scales, upturned mouth and no barbels.

Both are regulated tightly in many jurisdictions, and both are worth reporting where they are not established. Counting fin rays covers the technique where a positive identification is needed for a report.

Mirror and leather carp

Common carp come in scale variants that confuse people badly. Mirror carp have a scattering of large irregular scales rather than full coverage; leather carp have almost none.

Both are common carp, both have the barbels, and both are frequently reported as unknown species because the scaling is so unlike the fully scaled form. The barbel check identifies them regardless of what the scales are doing.

Why suckers get a bad name

Suckers are widely dismissed as trash fish, and the reputation is mostly inherited rather than earned. Several species are sensitive to pollution and their presence indicates good water quality, which makes them useful indicators rather than a nuisance.

Redhorse in particular are demanding of clean gravel and moving water, and a river with a healthy redhorse population is a river in reasonable condition.