Perches are fishes.
They are classified in the Family Percidae.
The perch family is second only to the minnow family in diversity of North American fishes.
Perches are characterized by having two dorsal fins, thoracic pelvic fins with one spine and five rays and ctenoid scales.
Ctenoid scales are scales that have small projections from the rear edge. Only some categories of fishes have ctenoid scales.
In North America, all but three species in the Family Percidae are darters. There are some European species in this family that are not darters, too. Illinois is home to all three North American species in this family that are not darters as well as one species that is a nonnative invader from Europe.
We’ll look at the darters first.
Darters tend to live on the bottom of streams or lakes and dart about for food.
They generally do not have a gas bladder, as some fishes do, so changing depth in the water is not easy for them.
Most of them are small animals. The largest darter species in Illinois is the logperch (Percina caprodes). At four to six inches in length, it is two to three times bigger than most of our other darter species.
The three North American perch that are not darters can all be found in Illinois. They are the yellow perch, sauger and walleye. One European species is also found in the waters of our state.