All About This Favorite Fish

The Growth Rate Chart: Comparison of average mean back-calculated length at each age for walleyes in South Dakota and Minnesota. Age Determination: Scale reading has been the traditional method for determining the age of fish and the average growth rate of populations. The assumption is that scales grow proportionately with fish length. And this relationship usually holds true. During periods of slow or no growth, as in winter, rings, called circuli, are narrowly spaced. Fast growth brings widely spaced circuli. Year marks or annuli show rather clearly under magnification, and measurements from the central focus to succeeding annuli provide the fish’s growth history. Scales of slow-growing fish or fish from consistently warm climates may not reveal true age. For these fish, otoliths (ear bones) are more accurate. But they must be removed from the skull and usually sectioned, a more difficult process than scale reading.

The most sensitive sniffer is the eel, capable of detecting amino acids in the range of a few parts per quadrillion. Although we know of no studies on the olfactory acuity of walleyes, it seems they probably can detect amino acids in a dilution of several parts per 10 million. That’s acute, for a part per million is about one ounce of a pure substance dissolved in enough water to fill 1,000 railroad tank cars.

In hatchery tests, researchers lured young walleyes up one side of a y-shaped maze by dripping solutions of amino acids, including betaine into one side. Salt solutions also proved attractive. Other amino acids, fish mucus, and essences of walleye body parts were repulsive to the fish.

It’s no surprise that walleyes smell well, for livebait often is the only answer to a tough bite and inactive fish. Sometimes the addition of a bit of crawler or minnow head provides a trigger that we surmise is due primarily to olfaction.

For walleyes, the sense of taste spurs a decision to spit a bait or to swallow it. Here again, a jig tipped with a minnow passes the taste test more often than one tipped with a twister tail. Researchers at Berkley, Classic Manufacturing, Kodiak, and other companies that produce plastics impregnated with attractants hope to eventually synthesize a formula more appealing than natural prey to walleyes and other species. Certainly, plastics flavored with attractive amino acids, preyfish essences, and salt cause fish to hold them in their mouth and sometimes attempt to swallow them.

Vision: Nighttime walleye fishing is a summertime tradition, but it’s also one of the best times to catch walleyes in winter, spring, and fall, particularly in clear lakes and reservoirs. Walleyes feed nocturnally because they see better at night than the prey they pursue. The only freshwater fish with better night vision is the walleye’s cousin, the sauger.

The walleye’s eye is large, allowing the pupil, the light gathering part of the eye, to gather as much light as possible. No creature can see in complete darkness, but starlight provides enough light for walleyes and other nocturnal animals. The principal adaptation for night vision in nocturnal animals is the tapetum lucidum, a reflective layer on the retina that concentrates light after it enters the eye. Cats, raccoons, skunks, and deer in addition to walleyes, sauger, and some other fish have similar structures.

Vision begins when light passes through the cornea and then the lens, which focuses the image as a camera lens does. Light then reaches two types of light-sensitive cells in the retina—rods and cones. Cone cells detect color when they’re exposed to daylight. Rod cells distinguish shades of gray and allow vision when sunlight isn’t present. Walleye and sauger eyes contain a larger proportion of rods than the eyes of perch, shiners, and other fish most active in daytime.

The tapetum lucidum, a layer of guanine crystals, is located in the lower portion of the deepest layer of the retina. This physiology suggests that walleyes see lures and baits moving above them more clearly than those moving slightly below their level. And fishing experiences suggest that for the best response, lures should be set to run slightly above sonar images of fish. Luminous paint or strips of tape applied to a crankbait belly catch the fish’s eye.