Perch belong to the class Osteicthyes, whose members have a skeleton of bone rather than cartilage. Bony fish comprise the largest group of vertebrates living today, both in the number of individuals (millions) and in the number of species (about 30,000). Perch occur in both fresh water and sea water throughout the entire world. Perch live at depths in the oceans as great as 7 mi (11.5 km) and in mountain streams or lakes as much as 3 mi (5 km) above sea level.
Perch belong to Order Perciformes in the sub-class Actinapterygii, the ray-finned fish, whose fins are supported by jointed rays, and which have large eyes, no internal nostrils, and a swim bladder. The Order Perciformes is the largest order of fishes, with 150 families, 1,367 genera, and 7,791 species. Members of this order usually bear spines on their fins, have scales with serrated edges, and a tail fin with 17 rays. The Perciformes are the most diverse of all fish orders and are dominant forms in both marine habits (75% of the species) and freshwater habits (25% of the species). Members of the order Perciformes include swordfish, tuna, mackerel, gobies, blennies, mullets, cichlids, and remoras. Two suborders (Percoidei and Gobioidei) include well over half of all species of perch. The Percoidei is the largest suborder with about 3524 species, many of which are desirable as human food-fishes, including striped bass, bluefish, snappers, barracudas, sunfishes, and perches. The family Percidae, with 9 genera and 146 species, includes all of the freshwater perches found in the northern hemisphere. Ninety percent of these species occur in North America east of the Rocky Mountains and most of these are darters. The Order Perciformes is characterized by two dorsal fins, one or two anal spines, and pelvic fins on the ventral, anterior trunk, with the base of the pelvic fin located forward of the pectoral fin. The vertebrae of perch number between 32 and 50; the largest species is the Walleye measuring some 90 cm (3 ft).
The genus Perca has three species: Perca fluviatilis, a Eurasian species; the yellow perch, Perca flavescens of North America; and Perca shrenki of Asia. All three species are generalized forms that probably represent the ancestral type from which the other species were derived.
The Old World counterpart of the yellow perch is the European perch, Perca fluviatilis. The two species are extremely similar and are separable only by minor differences; consequently, the classification of these two forms as two species or a single species is controversial.
The yellow perch is the preferred freshwater fish of many commercial fisheries in the United States. In the Great Lakes region of the United States and Canada commercial fisheries take between 5,000 and 10,000 tons of yellow perch per year from Lake Erie. This tonnage fluctuates from year to year due to fish population changes and to economic factors involved in delivering the catch to consumers. In Europe, perch are more popular as a sport fish than a commercial fish. Perch are very popular sport fish in Finland and in land-locked countries such as Switzerland. They are less popular in Great Britain and other countries with a significant salmon fishery.
Craig, J.F. The Biology of Perch and Related Fish. London: Croom Helm, 1987.
Rosen, Kenneth. Elementary Number Theory and Its Applications. 4th ed. Boston: Addison-Wesley, 2000.
Whiteman, Kate. World Encyclopedia of Fish & Shellfish. New York: Lorenz Books, 2000.