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.

Walleye fry seek light until they’re 1 to 1.5 inches long, when they gradually become photonegative, seeking dim light during bright periods. During the day, adult walleyes often hold in cover and in deeper water during the brightest parts of the day. They frequently move inshore at night, feeding most actively during low-light hours.

The pH of prime walleye waters ranges from 6.0 to 8.0. Walleyes seem to display no behavioral changes at pH levels within that range. Below 6.0, walleye spawning and recruitment often fail, while pH levels over 9.0 are unsuitable to most freshwater fish.

Adult walleyes often inhabit areas with current, except during winter when they tend to avoid all but the slightest current. Walleyes can swim for only about 10 minutes in water flowing 2.5 feet per second. They seek current breaks to conserve energy, while remaining in range of potential prey.

Walleye larvae hatched in rivers rely on current to transport them downstream toward plankton-rich waters before their yolk sacs are absorbed (3 to 5 days). If current is absent, they starve. Fry don’t begin to feed, however, until water temperatures reach the upper 50°F range.

Lab tests have shown that walleyes grow fastest at temperatures between 68°F and 75°F, avoiding water over 75°F. Growth of adults apparently stops below 53°F, and temperatures between 84°F and 95°F have proven fatal. Like most other freshwater fish, walleyes thrive in water containing at least 5 parts per million (ppm) of dissolved oxygen (DO). Adult fish can tolerate 2 ppm for short periods, while fry require 5 ppm.

Senses

Walleyes learn about their environment using the five senses we’re most familiar with (smell, taste, feel, hearing, and vision), plus an additional lateral line sense that receives low-frequency underwater vibrations. Sensory lobes compose a large portion of a walleye’s brain. Survival, growth, and reproduction depend on the function of these lobes.

Smell and Taste: The senses of smell and taste are linked in humans, making it difficult to tell a bite of apple from a bite of potato without smelling them. For fish, these senses are linked even closer because both detect molecules of substances dissolved in water. This makes determining whether a behavior is due to smell or to taste difficult.

Chemoreception in fish (including both smell and taste) is critical for finding prey, avoiding predators, locating fish of the same species, coordinating spawning time, and homing to residence areas or spawning sites. Sense of smell (olfaction) is primarily important for detecting distant substances, while for most fish, taste (gustation), determines the palatability of a substance once it’s taken into the mouth.

Walleyes have paired “nares” located along the top of the head toward the upper jaw that sense molecules dissolved in water. As the fish swims or remains still in moving water, molecules pass through the nares and contact the olfactory organ, which includes the olfactory lobe. In addition, the nares contain tiny hairlike cilia that create water movement through the nares, even when a walleye is still.

The olfactory organ contains folds, thought to enhance the sense of smell, since its surface contains receptor cells, and the number of receptor cells increases with the surface area of the olfactory organ. Walleyes have about 29 folds in their nares, a medium number between the channel catfish with 142 and members of the sunfish family with about 10.