Walleye Culture in Minnesota
Walleye is indisputably the king fish of the north. No other species elicits as much passion from the avid angler, or is more sought after. Consequently, there is great interest in intensively culturing walleye to food size. Unfortunately, because of certain characteristics (including intractable feeding habits and a tendency toward cannibalism when young), walleye are very difficult to culture. As a result, farmers have been limited to raising fingerlings in semi-natural ponds for stocking into natural bodies of water.
In an effort to investigate the potential for walleye culture in Minnesota, a demonstration project was included as part of the Minnesota Aquaculture Development and Education Program (MADEP). The objective was to provide a first step toward designing a profitable production system for food-size walleye. The project addressed questions of walleye growth rates in captivity, time needed to achieve market size, and the use of artificial feed.
Four private farmers from different areas of Minnesota participated in the project by raising walleye in existing ponds. One participant was in the far northwestern corner of the state, one in the southwest, and two in east-central Minnesota. Because some of the ponds were not drainable, cages were constructed for raising the fish. The cages allowed the walleye to be easily sampled, harvested, and monitored. They also confined the fish, and thus increased the likelihood that they would stay on dry feed.
In the wild, walleye feed exclusively on living organisms, such as zooplankton, insects, and other fish. This preference is so strong that many walleye will starve to death before they will eat artificial feed. When farmers try to train walleye to eat artificial feed, mortality rates of 50 to 90 percent are common. This training process is costly and requires a high capital investment, intensive labor, and expensive feeds. Newly hatched fry must be confined to indoor tanks where light, water quality, and feeding can be tightly controlled, and food must be provided constantly for up to one and one-half months. In addition, the feed must be formulated to exacting standards and contain large amounts of protein.
One major source of fry mortality during training is non-inflation of the swim bladder (an organ used to maintain buoyancy) after hatching. This organ must be inflated when fry are very young or they will sink to the bottom of the tank and die. Although the cause of this problem is not yet well understood, it is the subject of much current research. Another major source of mortality is cannibalism. With no natural feed available, fry will eat each other. After hatching, one fry can eat another that is almost equal in size. As they grow older, a larger size difference is required.
If walleye trained to eat artificial feed are stocked in a pond where natural feed is also available, they may switch back to the natural feed. Even when this supply can no longer support them, they may not return to eating the artificial food and their growth may slow.
Because they are carnivores, walleye have a high protein requirement, which typically means feeding costs are relatively high. Research is being done to more precisely determine their nutritional requirements.
Walleye are crepuscular fish. They tend to feed when light levels are low, such as at dawn, dusk, and before rainstorms. In very turbid water, they may be active during the day as well. A layer in their eyes, the tapitum lucitum, gathers light and provides them with excellent night vision. This affinity for low light may be an important consideration when determining feeding regimes and designing walleye culture facilities.
Walleye do have some advantages as a culture species. They tolerate a wide range of physical and chemical conditions. This tolerance is related to their natural environment, which is typically large, semi-turbid waters, where temperature and water quality vary considerably. Although they tolerate temperatures between 4°C (39°F) and 30°C (86°F), walleye grow best between 20°C (68°F) and 23°C (73°F). Spawning occurs shortly after ice-out in spring when temperatures are between 7°C (45°F) and 9°C (48°F). They can withstand dissolved oxygen levels as low as three parts per million (ppm) and have been known to withstand two ppm for extended periods in the lab. This hardiness is important because daily and seasonal changes are common in intensive outdoor culture systems.
Male walleye mature at two to four years, at 280 mm (10.9”) in length, while females mature at three to six years, when they are 350 to 430 mm (13.6” - 16.8”) long. The females spawn in shallow water where oxygen levels are high, and prefer sand, gravel, or rocks as substrate. Group spawning appears to be common. During spawning, milt and eggs are released into the water column, where they fuse and settle to the bottom. On average, 60,000 eggs are released per kilogram of female. The life expectancy of a walleye is five to seven years in southerly, warmer climates and 12 to 15 years in northern areas.
In July 1989, 16,000 walleye fingerlings were trapped from ponds in Erskine, Minnesota, and transported to the Leech Lake Reservation Fisheries Department Hatchery. They were trained to eat a dry diet in three separate indoor raceways at 20°C (68°F) over five weeks. During the first five days, they were fed Dry-Feed Kyowa C-1700, dispensed by electronically triggered automatic feeders at a rate of 10 percent of the total body weight per day. After this, they were switched to Dry-Feed Kyowa C-2700, then seven days later to a grower diet called Bio-dry 4000. Raceways were cleaned daily to maintain good water quality.
During the five weeks of conversion, four grow-out sites were prepared with docks, cages, and aeration. Initially, one cage was built at each site and aeration systems, which ran continuously throughout the two-year project, were installed. Cages were constructed to be very light, strong, easy to clean, inexpensive, and simple to build. The dimensions were six feet long by three feet wide by six feet deep. The total volume was 108 cubic feet. The frame was built of one-inch PVC tubing, which is light, cheap, and easy to use. Quarter-inch mesh Vexar plastic netting was attached to the frame to contain the fish. This was small enough to keep the fish from escaping, but large enough to limit fouling. Floatation was provided by closed-cell, rigid polystyrene foam mounted under the wooden cover. The total cost was $158.91 per cage.
On August 24, approximately 20.5 pounds of fish at 85 fish per pound were delivered to each site. They were allowed to grow until they reached a maximum density of 0.5 pounds of fish per cubic foot of cage, (54 pounds per cage). At that point, another cage was built and the walleye were divided between the two. The southwestern site and one of the east-central sites each had six cages by the end of the project, while the other east-central site had two, and the northwestern site had one.
After stocking, the walleye were fed Bio-dry 4000 for a period of time and then switched to a salmon diet. As the fish grew, they were fed progressively larger pellets. The feeding ration ranged from five percent body weight per day in summer to one percent body weight per day in winter. An automatic cage-mounted belt feeder (made by Zeigler Bros., Inc.) was used to provide the feed throughout the day.
Water quality and fish growth were monitored throughout the project. Dissolved oxygen, carbon dioxide, pH, and water temperature measurements were taken three times each week and total alkalinity, total hardness, and ammonia nitrogen were monitored. Periodic, random samplings were conducted to measure walleye weight and length and to check for signs of stress or disease.
Summary of Project Result
Individual growth rates varied a great deal between the four sites (Figs. 1 and 2). By mid-summer 1991, walleye at the southwestern site (where the fastest growth occurred) weighed an average of 0.37 pounds each, while at one of the east-central sites, they weighed 0.01 pounds. Walleye at the southwestern site, which were allowed to continue to grow beyond the end of the project, were again sampled in October, 1992. Their average weight was 0.44 pounds. and their length ranged from 9.9 inches to 14.2 inches. The range of weights was from 0.34 pounds to 1.2 pounds.
Mortality varied between sites. At the southwestern site, 1,077 of the original 1,760 stocked fish, or 61.2 percent, remained by June 1991. At the northwestern site, 200 fish, or 11.4 percent survived. Two major problems affected survival. At one site, the walleye succumbed to a Trichodina infection. Although the walleye were treated and the disease was eliminated, it caused heavy losses. At one of the east-central sites, survival had been 65.9 percent through June 1991. However, at the beginning of June, all the walleye died from an unknown cause. They were examined by diagnostic laboratories at Purina Mills and the Minnesota Department of Agriculture but nothing definitive was found. Two of the most likely possibilities were: (1) the pond was struck by lightening during a storm, or (2) the storm flushed contaminants from surrounding agricultural lands into the water.
Walleye were able to thrive, and at least a portion of the crop, reached market size in two growing seasons. However, had this been a commercial venture, it would have lost money. A number of factors, including high feed costs and low loading rates, contributed to the loss.
Feed costs were high for two reasons. First, because of the high protein content, the price of the feed itself was high. Second, the conversion of feed to fish flesh was very poor. This may have been largely due to uneaten feed simply falling through the cage. Research is currently underway on the nutritional requirements of walleye to better tailor the feed to their specific needs. Related to this, research needs to be done regarding the most efficient methods, frequency, and quantity for feeding. With improvements in these areas, the conversion ratio of feed to fish flesh will improve, allowing higher yields at lower cost.
Loading densities were kept conservatively low. This resulted in inefficient use of space, high construction costs, and low overall yield. Other cage-cultured species are commonly stocked four times more densely. More research must be completed on optimal stocking densities for ponds and cages.
Another critical area of work for both public and private researchers is the development of domesticated lines of walleye for intensive culture. Animals caught from the wild cannot be expected to perform as well as domesticated strains raised in intensive culture. They are not as resistant to disease, cannot convert artificial feed as efficiently, nor do they respond well to a wide array of conditions found in a culture situation. With a selective breeding program, a domesticated line of walleye may be developed that will thrive in captivity.
- Stickney, R. 1986. Culture of Nonsalmonid Freshwater Fishes. Boca Raton, FL. CRC Press.
- Krise, W. F. and J. W. Meade. 1986. Review of the intensive culture of walleye fry. Progressive Fish Culturist. 48(2): 81-87.
- Buttner, J. K. 1989. Culture of fingerling walleye in earthen ponds. Aquaculture Magazine. March/April: 37-46.
- Malison, J. A. et al. 1990. Comparative survival, growth, and reproductive development of juvenile walleye and sauger and their hybrids reared under intensive culture conditions. Progressive Fish Culturist. 52(2): 73-82.
- Harding, L. M., C. P. Clouse, R.C. Summerfelt, and J. E. Morris. 1992. Pond Culture of Walleye Fingerlings. North Central Regional Aquaculture Center Fact Sheet Series #102.
Special thanks are owed to the private cooperators who cared for the fish on a day-to-day basis: Clarence Espeseth of the Cross Lake Association; Jessie Preiner of Trout-Air, Inc.; Ron Reardon of Golden Ponds; John Ringle of the Leech Lake Indian Reservation Fisheries Department; and Don Winson of Spring Creek Trout Farm. Les Getting, with the University of Minnesota, coordinated the bulk of the project, and deserves special thanks. Finally, thanks to those who commented on and edited the text of this publication.
Funding for the Minnesota Aquaculture Development and Education Program was approved by the Minnesota Legislature (ML 1989, Chapter 335, Art. 1, Sec. 29, Subd. 11(P)) as recommended by the Legislative Commission on Minnesota Resources from the Minnesota Future Resources Fund. The funding ran from July 1, 1989, to June 30, 1991. It was a cooperative effort between the University of Minnesota, state agencies and the private sector. Researchers and extension staff of the University of Minnesota Department of Fisheries and Wildlife and Minnesota Sea Grant College Program designed and ran the program. Cooperators from the private sector provided the facilities, and volunteered their time for day-to-day management of the fish. Other groups involved included NRRI Business group, and the Minnesota Extension Service.
By Jeff Mittelmark and Anne Kapuscinski