The walleye (Sander vitreus, synonym Stizostedion vitreum), also called the yellow pike, is a freshwater perciform fish native to most of Canada and to the Northern United States. It is a North American close relative of the European zander, also known as the pikeperch. The walleye is sometimes called the yellow walleye to distinguish it from the blue walleye, which is a subspecies that was once found in the southern Ontario and Quebec regions, but is now presumed extinct. However, recent genetic analysis of a preserved (frozen) 'blue walleye' sample suggests that the blue and yellow walleye were simply phenotypes within the same species and do not merit separate taxonomic classification.
Walleyes show a fair amount of variation across watersheds. In general, fish within a watershed are quite similar and are genetically distinct from those of nearby watersheds. The species has been artificially propagated for over a century and has been planted on top of existing populations or introduced into waters naturally devoid of the species, sometimes reducing the overall genetic distinctiveness of populations.
The common name, "walleye", comes from the fact that the fish's eyes point outward, as if looking at the walls. This externally facing orientation of the eyes gives anglers an advantage in the dark because a certain eyeshine is given off by the eye of the walleye in the dark, similar to that of lions and other nocturnal animals. This "eyeshine" is the result of a light-gathering layer in the eyes called the tapetum lucidum, which allows the fish to see well in low-light conditions. In fact, many anglers look for walleyes at night since this is when major feeding efforts occur. The fish's eyes also allow them to see well in turbid waters (stained or rough, breaking waters), which gives them an advantage over their prey. Thus, walleye anglers commonly look for locations where a good "walleye chop" (i.e., rough water) occurs. This excellent vision also allows the fish to populate the deeper regions in a lake, and they can often be found in deeper water, particularly during the warmest part of the summer and at night.
Walleyes are largely olive and gold in color (hence the French common name: doré--golden). The dorsal side of a walleye is olive, grading into a golden hue on the flanks. The olive/gold pattern is broken up by five darker saddles that extend to the upper sides. The color shades to white on the belly. The mouth of a walleye is large and is armed with many sharp teeth. The first dorsal and anal fins are spinous, as is the operculum. Walleyes are distinguished from their close relative the sauger by the white coloration on the lower lobe of the caudal fin, which is absent on the sauger. In addition, the two dorsals and the caudal fin of the sauger are marked with distinctive rows of black dots which are absent from or indistinct on the same fins of walleyes.
Walleyes grow to about 80 cm (31 in) in length, and weigh up to about 9 kg (20 lb). The maximum recorded size for the fish is 107 cm (42 in) in length and 13 kilograms (29 lb) in weight. The rate depends partly on where in their range they occur, with southern populations often growing faster and larger. In general, females grow larger than males. Walleyes may live for decades; the maximum recorded age is 29 years. In heavily fished populations, however, few walleye older than five or six years of age are encountered. In North America, where they are highly prized, their typical size when caught is on the order of 30 to 50 cm (12 to 20 in), substantially below their potential size.
As walleye grow longer, they increase in weight. The relationship between total length (L) and total weight (W) for nearly all species of fish can be expressed by an equation of the form
Invariably, b is close to 3.0 for all species, and c is a constant that varies among species. For walleye, b = 3.180 and c = 0.000228 (with units in inches and pounds) or b = 3.180 and c = 0.000005337 (with units in cm and kg).
This relationship suggests a 50 cm (20 in) walleye will weigh about 1.5 kg (3.3 lb), while a 60 cm (24 in) walleye will likely weigh about 2.5 kg (5.5 lb).
In most of the species' range, male walleyes mature sexually between three and four years of age. Females normally mature about a year later. Adults migrate to tributary streams in late winter or early spring to lay eggs over gravel and rock, although open-water reef or shoal-spawning strains are seen, as well. Some populations are known to spawn on sand or vegetation. Spawning occurs at water temperatures of 6 to 10 °C (43 to 50 °F). A large female can lay up to 500,000 eggs, and no care is given by the parents to the eggs or fry. The eggs are slightly adhesive and fall into spaces between rocks. The incubation period for the embryos is temperature-dependent, but generally lasts from 12 to 30 days. After hatching, the free-swimming embryos spend about a week absorbing a relatively small amount of yolk. Once the yolk has been fully absorbed, the young walleyes begin to feed on invertebrates, such as fly larvæ and zooplankton. After 40 to 60 days, juvenile walleyes become piscivorous. Thenceforth, both juvenile and adult walleyes eat fish almost exclusively, frequently yellow perch or ciscoes, moving onto bars and shoals at night to feed. Walleye also feed heavily on crayfish, minnows, and leeches.
The walleye is considered to be a quite palatable freshwater fish, and consequently, is fished recreationally and commercially for food. Because of its nocturnal feeding habits, it is most easily caught at night using live minnows or lures that mimic small fish. In Minnesota, the walleye is often fished for in the late afternoon on windy days (known as a "walleye chop") or at night. Most commercial fisheries for walleye are situated in the Canadian waters of the Great Lakes. Often served as a sandwich in Minnesota's pubs where the fish is very popular, deep fried walleye on a stick is a Minnesota State Fair food.
Because walleyes are popular with anglers, fishing for walleyes is regulated by most natural resource agencies. Management may include the use of quotas and length limits to ensure that populations are not overexploited. For example, in Michigan, walleyes shorter than 15 in (38 cm) may not be legally kept, except in Lake St. Clair and the St. Clair River, where fish as short as 13 in (33 cm) may be taken.
Since walleyes have excellent visual acuity under low illumination levels, they tend to feed more extensively at dawn and dusk, on cloudy or overcast days, and under choppy conditions when light penetration into the water column is disrupted. Although anglers interpret this as light avoidance, it is merely an expression of the walleyes' competitive advantage over their prey under those conditions. Similarly, in darkly stained or turbid waters, walleyes tend to feed throughout the day. In the spring and fall, walleyes are located near the shallower areas due to the spawning grounds, and they are most often located in shallower areas during higher winds due to the murkier, higher oxygenated water at around six feet deep. On calm spring days, walleyes are more often located at the deep side of the shoreline drop-off and around shore slopes around or deeper than 10 feet.
As a result of their widespread presence in Canada and the northern United States, walleyes are frequently caught while ice fishing, a popular winter pastime throughout those regions.
"Walleye chop" is a term used by walleye anglers for rough water typically with winds of 10 to 25 km/h (6 to 16 mph), and is one of the indicators for good walleye fishing due to the walleyes' increased feeding activity during such conditions. In addition to fishing this chop, night fishing with live bait can be very effective.
The current all-tackle world record for a walleye is held by Mabry Harper, who caught an 11.34-kg (25-lb) walleye in Old Hickory Lake in Tennessee on August 2, 1960.
It is very popular with Minnesota residents; more walleye is eaten in Minnesota than in any other jurisdiction of the United States. Both Garrison and Baudette, Minnesota, claim to be the "Walleye Capital of the World", each with a large statue of the fish.
Winnipeg, Manitoba, considers the walleye (referred to locally as "pickerel") its most important local fish.:76 Icelandic fishermen in Lake Winnipeg have traditionally supplied the Winnipeg market.:23-26