Bergerhouse, D. L. 1996. Cage culture of walleye. Pages 251-260 in R. C. Summerfelt, editor. 

Walleye culture manual. NCRAC Culture Series 101. North Central Regional Aquaculture 

Center Publications Office, Iowa State University, Ames. 

Cage Culture of Walleye 

David L. Bergerhouse, Quad Cities Spray Canal Project, c/o Commonwealth Edison, Cordova, lL 61242 

Introduction 

Cage culture can be defined as the raising of aquatic 

organisms in an enclosure within a larger body of water. 

Although cage culture of walleye is not a well-established practice, the four case studies included in this 

chapter demonstrate that walleye can survive in cages, 

can be trained (habituated) to accept artificial feed in 

cages, can be over-wintered in cages in temperate 

regions, and can grow to a size at which they are 

marketable as a food fish. The initial capital investment 

required to begin raising fish in cages in existing water 

bodies is much less than that required for construction 

of drainable ponds or an intensive culture system. 

Therefore, cage culture may very well contribute to the 

development of walleye as a commercial species. 

Advantages of cage culture 

General concepts 

There are a number of advantages to culturing fish in an 

enclosure. Cage culture of walleye does not require 

expensive tank or raceway facilities, and usually does 

not require continuous pumping of large quantities of 

water. The capital and overhead costs of walleye cage 

culture would therefore be somewhat less than for other 

types of walleye culture. Cages allow the use of existing 

water bodies that would otherwise not be suitable for 

aquaculture due to their size, bottom configuration, lack 

of drainability, or the presence of obstructions which 

make seining impractical. Cage culture may be the only 

practical aquaculture method in these waters. When 

existing water bodies are used, the initial cost of pond 

construction is avoided (Masser 1988a; Swann et al. 

1994). 

It is easier to monitor the health and growth of fish in a 

cage than in open ponds. Sampling and harvest are 

simpler and require less equipment. In some cases a 

pond used for cage culture can be used to grow a 

second crop outside the cages, a form of polyculture, or 

for sport fishing or other recreational activities (Masser 

1988a). 

Walleye culture in cages 

There are several advantages to raising walleye in 

cages. Walleye generally do not respond to feed spread 

on an open pond as well as some other cultured species. 

When walleye are confined to cages, however, they can 

be habituated to a prepared &et, because the fish are 

concentrated near the feed. 

In ponds, tanks, or cages, walleye will cannibalize 

smaller siblings when size differences are sufficiently 

great. Antagonistic behaviors (hierarchy and territorial 

defense) of some fish species break down in the close 

confinement of cages, but there is no evidence that 

cannibalism by walleye is decreased by crowding. 

However, cages allow fish to be observed and graded to 

maintain a uniform size and they facilitate handremoval of cannibals. 

Walleye possess several characteristics that make them 

an attractive choice as a culture animal. Walleye are 

highly regarded both as a sport fish and as a food fish. 

Market potential exists both for fingerlings for stocking 

to enhance sport fisheries, and for larger fish for human 

consumption. Additionally, walleye are a coolwater fish. 

In temperate regions they may be better suited for cage 

culture than warmwater species because they will feed 

and grow at cooler water temperatures. The growing 

season for walleye would therefore begin earlier in the 

spring and extend later in the fall than for warmwater 

species. 

NCRAC Culture Series 101 - Walleye Culture Manual 251 
Disadvantages of cage culture 

General concepts 

There are a number of disadvantages to raising fish in 

cages. Concentrating fish in a small area can lead to 

degraded water quality conditions in a localized area 

around the cage. Low dissolved oxygen or a hgh 

concentration of ammonia in the cage can cause stress 

or mortality even though the overall pond environment 

remains suitable for survival. When water quality 

deteriorates, caged fish are not free to seek areas where 

conditions are more favorable. 

Considerable time and labor may be required to clean 

cages. Fish in a cage are dependent on the movement of 

water through the mesh to flush away waste and to 

replenish oxygen. Because biofouling of the mesh can 

restrict water movement through a cage, cages need to 

be cleaned regularly. 

When fish are crowded into a small area the potential 

for disease increases. Fish that are crowded may 

become stressed and, therefore, vulnerable to infection. 

The close confinement of fish in cages can lead to the 

rapid spread of infectious dseases. Inappropriate cage 

materials or design can lead to abrasions or injury 

which in turn provide opportunities for infection. 

Treatment of fish in cages can be difficult. 

Fish in cages may exhibit antagonistic or territorial 

behaviors which can interfere with feeding and uniform 

growth. Fighting or biting can cause injury which may 

lead to infection. 

Caged fish have little opportunity to acquire natural 

forage. Therefore, a nutritionally complete diet must be 

provided in order to obtain good growth rates and 

healthy fish. 

Finally, fish can be lost from a cage in several ways. A 

small hole in a cage may allow the fish to escape. 

Escaped fish may be lost if the water body cannot be 

harvested. Fish in cages are more vulnerable to poaching or vandalism than fish cultured in open ponds. 

Predation by birds or snakes may be serious if the cage 

is not properly covered. 

Walleye culture in cages 

There are specific problems involved with raising 

walleye in cages. Pond-cultured walleye must be trained 

to accept a prepared diet, which can be done in cages 

(Harder and Summerfelt 1996), or in tanks. However, 

considerable mortality from disease, starvation, or 

cannibalism can occur during training. Although feedtrained fingerlings may be purchased from private 

producers, reliable sources are not always nearby and 

they may be costly. 

Walleye are sensitive to disturbance; they may be 

stressed by handling or activity related to cleaning or 

maintenance of the cage. When stressed or injured, they 

are very susceptible to hsease, especially if the 

temperature exceeds 77°F (>25"C). Also, walleye must 

be graded to prevent cannibalism or competition and 

sampled to adjust feeding rates; therefore, there is a 

high probability of significant mortality due to handling 

stress and disease. 

Site selection 

walleye have been raised in cages in many types of 

water bodies including strip pits (Stevens 1996; Harder 

and Summerfelt 1996), borrow pits, lakes (Blazek 

1996), and farm ponds (Anderson and Budiselich 199 1 ; 

Bushman 1996). There are an number of site selection 

criteria that should be met before cage culture is 

attempted (Masser 1988a; Selock 1990; Swann et al. 

1994): 

The pond should be large enough to support the 

number of fish in the cage. Biological processes 

in the pond environment break down metabolic 

wastes and produce oxygen. Most ponds can 

support only about 1,000-1,500 lbs/acre (1 136- 

1 704 kg/ha) without supplemental aeration or 

water flow. Confining fish in cages does not 

increase the carrying capacity of the pond. Waste 

feed, feces, and ammonia excretion will add a 

nutrient load to the pond. This may increase 

algae, macrophytes, and potential for oxygen 

depletion. 

The pond should not have a large biomass of fish 

outside of the cage. These fish must be included 

in the total carrying capacity of the pond. 

The pond should not be located in a watershed 

where the pond will receive agricultural runoff, 

livestock waste, or pesticide contamination. 

Nutrients from agricultural runoff or livestock 

waste can increase biological oxygen demand 

(BOD) resulting in low dissolved oxygen, and 

nutrients can cause excessive phytoplankton 

252 NCRAC Culture Series 101- Walleye Culture Manual 
blooms leading to drastic swings in oxygen 

concentrations (Anderson and Buhselich 1991). 

Pesticides can kill fish directly or contaminate 

their flesh. 

The site for the cage should be deep enough to 

allow waste materials to be swept away from the 

cage. At least 1-2 ft (0.3 to 0.6 m) of water should 

be kept between the cage bottom and the pond 

bottom (Selock 1990). The water level in the 

pond should not fluctuate significantly. The pond 

should be exposed to wind action to aid in water 

circulation through the cage. 

The pond must be accessible. Cage culture 

requires regular maintenance and feeding, so easy 

access to the cage is important. If aeration is to be 

used, access to a power source is important. It is 

desirable for the pond to be in a controlled or 

secure area to minimize poaching. 

Types of walleye cage culture 

There are four types of end products of walleye cage 

culture. They are: 

1. Small fingerlings, 1.5-2.5 in (38-64 mm), for 

2. Feed-trained fingerlings, 2.5-3.5 in (64-89 mm), 

3. Advanced fingerlings >6 in (>152mm) for 

4. Food fish 14 to 16 in and larger (356-406+ mm). 

The type of cage and methods used will depend on 

stoclung. 

for sale to other producers. 

stocking. 

the desired end product. 

Procedures for producing small fingerlings in ponds are 

well established (Buttner 1989; Harding et al. 1992; 

Summerfelt et al. 1994), and large numbers are produced annually at state and federal hatcheries. However, 

some work has been done culturing fry to the small 

fingerling stage in enclosures within a larger water 

body. Brugge and McQueen (1 991) constructed large 

circular enclosures of polyvinyl-coated nylon. Their 

structure did not allow any water exchange between the 

enclosure and the surroundmg water body. They were 

managed like small ponds, includmg fertilization to 

induce a high standing crop of zooplankton. The 

enclosures were stocked at rates ranging from 8,000 to 

32,000 fry per 35,300 ft3 (1,000 m3) enclosure. Survival 

at 50 d ranged from 25.4% to 45.3%, and mean fork 

length was 28.9 to 33.7 mm. The fingerlings could be 

released into the surrounding water body by simply 

lifting the sides of the enclosure. With these methods, 

small fingerlings could be produced within a lake that 

was to be stocked while avoiding the stress and mortalities often associated with harvesting, transporting and 

stocking of fingerlings produced in hatchery ponds. 

Feed-trained fingerlings produced in cages may be 

raised to produce either advanced fingerlings or food 

fish in cages. However, feed-trained fingerlings raised 

in cages could be marketed for grow out in other types 

of culture facilities. 

Advanced fingerlings (> 6 inches) can be produced in 

cages by the end of the first growing season for 

stocking recreational fishing lakes (Blazek 1996). There 

also may be a market for advanced fingerlings that have 

been over-wintered in cages. An advanced fingerling 

stocked in the spring would avoid heavy mortalities 

often associated with the first winter in the wild. 

The production of food fish in cages currently requires 

2 to 2.5 growing seasons (Stevens 1996). Improved 

walleye diets and culture techniques will probably 

allow this production time to be reduced in the near 

future. 

Cage design 

Criteria for cage design include size, number of cages, 

shape, mesh size, flotation, and means of access. 

Cages can range in size from the 1000-m3 enclosures 

used to raise fry to small fingerlings (Brugge and 

McQueen 1991) to about 1 m3. Cage size should be 

determined by the anticipated number of fish and 

desired size when the cage is harvested. Stochng 

densities can range from >3,600/m3 for training small 

pond-raised fingerlings to formulated feed to as few as 

1 7/m3 for raising advanced fingerlings to food-size fish 

(Table 1). A large cage is more cost effective in terms of 

cost per unit cage volume, but larger cages are more 

difficult to handle and harvest. Several small cages 

allow walleye to be graded and dwided as they grow. 

The number of cages in a pond should be determined by 

the capacity of the pond and the size and capacity of the 

cages. If the intent is to grow advanced fingerlings for 

stoclung, grading and dividmg may not be necessary, 

and a single large cage may be suitable. Food-size 

walleye will require at least two growing seasons to 

NCRAC Culture Series 101 - Walleye Culture Manual 253 
Table 1 Stocking density, growth and survival of walleye stocked into cages by case 

study authors. 

Cage 

volume 

(m3) 

3.6 

3.6 

3.6 

3.6 

3.3 

7.3 

7.3 

7.3 

7.3 

3.6 

1.42 

3.6 

3.6 

1.24 

1.24 

1.24 

1.24 

Cage 

shape 

* 

R 

R 

R 

R 

R 

R 

R 

R 

R 

R 

C 

R 

R 

C 

C 

C 

C 

Number 

stocked 

Initial Initial ) Final 

density length length 

(No Jmk) inches (mm) inches 

Mesh 

inches 

(mm) 

S u rvi va I 

("/I 

31 0 

400 

405 

485 

2500 

1000 

500 

250 

125 

822** 

358** 

580 

508 

440 

1012 

4448 

530 

Blaze k (1 996) 

86 3 (76) 5.2 (132) 

111 3.5 (89) 6.4 (163) 

112.5 2.25 (57) 6.1 (155) 

1 35 2.5 (63.5) 5.3 (134) 

Stevens (1 996) 

757 2.5 (63.5) 3.5 (89) 

1 37 3.5 (89) 8 (203) 

68 8 (203) 10 (254) 

17 14 (355) 16 (406) 

34 10 (254) 14 (355) 

Bushman (1 996) 

228 2.5 (63.5) 4.9 (124) 

252 2.5 (63.5) 4.9 (124) 

141 5.6 (142) 6 (152) 

161 2.4 (61) 3 (76) 

Harder and Summerfelt (1 996) 

354 2.5 (63.5) 5 (127) 

81 6 2.5 (63.5) 5 (127) 

427 6 (152) 

*** 361 9 1.9 (48) 

0.25 (6.35) 

0.25 (6.35) 

0.25 (6.35) 

0.25 (6.35) 

0.19 (4.8) 

0.25 (6.35) 

0.5 (1 2.7) 

0.5 (1 2.7) 

0.75 (19) 

0.25 (6.35) 

0.25 (6.35) 

0.25 (6.35) 

0.5 (1 2.7) 

0.25 (6.35) 

0.25 (6.35) 

0.25 (6.35) 

0.25 (6.35) 

84.3% 

71.5% 

26.6% 

55.3% 

33.5% 

36.6% 

93% 

98% 

6.5% 

6.5% 

22.8% 

* R- Rectangular, C-Circular 

** Hybrid walleye 

*** Divided into two cages represented by the following line. 

reach marketable size. Therefore, in planning a cage 

culture operation it may be necessary to account for two 

year-classes in the pond at the same time. A single cage 

with a small mesh size would not be suitable for raising 

walleye from a small fingerling to a food-size fish. As 

the fish grow, they should be graded, divided, and 

transferred to cages with larger mesh to allow better 

water circulation. Stevens (1996) used cages of four 

different mesh sizes over a span of three years to 

produce food-size walleye. By splitting the fish biomass 

into smaller cages they can be placed at several sites 

around the pond, thus reducing the possibility that 

water quality will become degraded around one large 

cage. 

Walleye have been raised in both rectangular and 

circular cages. At this time, there is no evidence to 

suggest that one shape is more suitable. Some species 

that tend to swim actively much of the time may benefit 

from a circular cage since the fish are not constantly 

running into corners which can cause abrasions. 

Designs for construction of circular and rectangular 

cages are readily available (Masser 1988b; McKee et al. 

1989; Swan 1990; Bushman 1996) and will not be 

254 NCRAC Culture Series 101- Walleye Culture Manual 
discussed. Other designs that could potentially be used 

include floating vertical raceways (Martin and Heard 

1987) and floating horizontal raceways (Figure 1). 

A small mesh will become blocked by biofouling 

organisms and debris more quickly than a large mesh. 

The mesh size chosen for a particular cage should be 

the largest mesh size that will still retain the smallest 

fish in the cage. Kindschi and Barrows (1991) reported 

an optimal mesh size to retain walleye fry of no more 

than 710 ptn between threads and no more than 53% 

open area. A mesh of this size in a pond environment 

would restrict water exchange and become fouled very 

quickly. No detailed work has been reported on the 

optimal mesh size to retain walleye fingerlings of 

various sizes. The best guide at this point is the criteria 

used by Stevens (1996): 0.19-in (4.8-mm) mesh for 

2.5-in (63.5-mm) fish, and gradually increases up to 

0.75-in (19-mm) mesh for 14-in (355-rnm) fish (Table 

1). The 0.19-in (4.8-mm) mesh may be smaller than 

necessary for 2.5 in fish, Harder and Summerfelt 

(1996) successfully used 0.25-in (6.35-mm) mesh for 

1.9-in (48-mm) fish. 

Most aquaculture cages are constructed with black 

plastic mesh designed specifically for aquaculture. 

Plastic mesh is easy to cut and it is very durable. If the 

cages are located in a water body with a large population of gnawing mammals, such as muskrats, there is a 

possibility that the muskrats will chew through the 

plastic mesh, and the fish will escape. Welded wire and 

hardware cloth have been used for cages, but these 

materials tend to rust. Vinyl-coated hardware cloth is 

somewhat more expensive than plastic, but has good 

durability and will resist the chewing efforts of muskrats. 

Flotation used for cages includes Styrofoam blocks, net 

floats, sealed plastic jugs, and sealed PVC pipe. Any of 

these may work depending on the particular application. 

It is important, however, to allow ample freeboard, that 

is the distance between the top of the cage and the 

water, to avoid possible submergence of the cage. The 

cage should have excess flotation sufficient to resist 

submergence. Ducks and other animals may find the 

cage a convenient place to rest, and add their weight to 

the flotation requirements of the cage (Harder and 

Summerfelt 1996). Plastic jugs may deteriorate and 

leak, which requires sufficient flotation so that the cage 

will remain afloat until a water filled jug float can be 

replaced. 

It may be desirable to attach the cage to a floating dock 

or a pier. A dock provides a stable anchorage, and a 

stable work platform for servicing the cage (Figure 1). 

Care must be taken however, to not cluster too many 

cages around a small dock in shallow water, because 

water exchange may be reduced and there may be 

insufficient depth between the bottom of the cage and 

the pond bottom. Cages not attached to a dock can be 

serviced by boat, but at times this can become awkward. 

Figure 1. A dock provides easy access and a stable work 

platform for servicing cages. However too many cages 

around a small dock in shallow water may lead to water 

quality problems. 

Source of walleye 

The source of fingerlings is one of the most important 

considerations in planning a walleye cage culture 

operation. At this time, there are few commercial 

sources for feed-trained fingerlings. Habituating pondreared fingerlings can be done in cages (Harder and 

Summerfelt 1991), but mortality will be an added 

expense. Also, transporting fish from the producer to 

the grow-out site and stocking them into a cage in good 

condition is another problem. Walleye are easily 

stressed by handling, and are highly susceptible to 

columnaris when stressed. Significant mortalities can 

and often do occur in the first 2 weeks after stocking 

(Harder and Summerfelt 1991 ; Harder 1992; Harder 

and Summerfelt 1996). It is vital to acquire the highest 

quality fish available and to handle them as little as 

possible when transporting them to the cage. UnfortuNCRAC Culture Series 101 - Walleye Culture Manual 255 
nately, walleye growers often have limited choices as to 

where they acquire their fish. The choice of suppliers of 

trained fingerlings is likely to increase as the walleye 

culture industry expands. Factors such as initial 

condition of fish, distance to be transported, and 

temperature change are all important considerations 

when selecting a source of fish. 

In northern Illinois, walleye raised in ponds will 

generally reach about 2 in (50.8 mm) by early-to midJune. If these fish are transferred to tanks and trained to 

accept artificial feed for 2-3 weeks, they should be 

ready for cage stocking in early July. Unfortunately, 

water temperatures in July can be warm enough to 

cause stress when the fish are stocked. Timing the cage 

stocking with cool water temperatures may help reduce 

stocking mortality. 

Significant advances are being made raising fish from 

the fry to fingerling stage entirely on artificial diets 

(Moore et al. 1994a, 1994b). If this technology is 

adopted by commercial producers, then the possibility 

of acquiring feed-trained walleye fingerlings in June, 

when water temperatures are relatively cool, may 

increase survival of fingerlings stocked in cages. 

Training and feeding 

walleye have been successfully trained in cages 

(Stevens 1996; Harder and Summerfelt 1996). Fingerlings to be trained in cages must be in good condition 

when stocked. They should be stocked at fairly high 

density and fed often. Stevens (1996) successfully 

trained walleye at a density of 21/ft3 (757/m3). A 

commercial vibrating feeder was used to feed the 

fingerlings once every 5 minutes 24 hlday. He started 

his fingerlings on Kyowa C-2000 (Biokyowa Inc., 

Chesterfield, MO) at 10% of their body weight per day, 

and then converted them to 4 granules of the W-16 diet 

(Westers and Stickney 1993). Once the fish were feedtrained they were fed W-16 diet at 3-4% of their body 

weight per day. This ration was divided between two 

feedmg periods. The fish were fed every 30 min for a 3 

h period just before daylight, and again for a 3 h period 

beginning just after dusk. 

Harder and Summerfelt (1 996) achieved their best 

results (22.8% survival to 6 in [152 mm]) when 

fingerlings were stocked at high density during training 

(103/ft3 [3,619/m3]) and then thinned for grow-out. 

They fed their fish once every 15 min for 17 h/day 

throughout the entire culture period. Their best results 

were achieved using Biotrainer and Biodry diets 

(Bioproducts, Warrenton, OR). 

Bushman (1996) started with feed-trained walleye 

fingerlings. He fed hs fish every 15 min 24 Idday on 

various combinations of Walleye Grower (Murray 

Elevators, Murray, Utah) and Biokyowa, then switched 

the fish to Silver Cup Salmon feed (Murray Elevators, 

Murray Utah) for grow-out. As water temperatures 

cooled in the fall the feedings were reduced to the 

periods around dawn and dusk. Survival ranged from 

93-98% though the mortality associated with training 

was not a factor. 

Blazek (1996) started with fish that were already 

trained to the W-16 &et. He set his timers to feed 48 

times per day, and achieved survival as high as 84%, 

though training mortalities were not included. 

High mortality can occur when cage-training walleye to 

formulated feed. Mortality is related to handling stress, 

disease, starvation, and cannibalism. Harder and 

Summerfelt (1996) achieved 54% survival when 

walleye were tank-trained to feed and then transferred 

to cages, but only 22.8% when they were cage-trained 

to feed. At present, tank-training walleye appears to be 

more effective than cage-training. However, they dd 

demonstrate that walleye can be trained in cages. As 

more experience is gained and techniques improve, 

training walleye in cages may become more effective. 

For walleye cage culture to develop, a source of high 

quality walleye diets must be available in the midwest 

so that feed can be purchased and shipped economically. In 1995, the 9206 Walleye Grower &et developed 

by ET. Barrows (National Biological Service, 

Bozeman, Montana) could be obtained from Nelson and 

Sons, Inc., Murray, Utah for about $0.40/lb ($0.88/kg) 

including the cost for shipping (A. Moore, Iowa 

Department of Natural Resources, personal communication). 

Plans for building inexpensive feeders suitable for cages 

are available (Mortensen 1987; Bushman 1996), 

however, some researchers who have used these feeders 

to feed walleye in cages have had difficulty achieving 

uniform and consistent feeding rates (Blazek 1996; 

Harder and Summerfelt 1996). These homemade 

256 NCRAC Culture Series 101- Walleye Culture Manual 
feeders may be suitable for feed-trained walleye but are 

not accurate or dependable enough to use when training 

walleye to accept artificial feed. A commercial vibrating 

feeder and timing system is considerably more expensive than the homemade feeder, but the cost may be 

justifiable, at least through the training period. 

The cage environment 

Environmental conditions must be maintained within a 

cage for walleye to obtain satisfactory growth and 

survival. The preferred temperature range for walleye 

growth is 68-77°F (20-25" C); the ideal temperature is 

73°F (23°C) (R.C. Summerfelt, Iowa State University, 

personal communication). However, the cage culturist 

has no control over water temperature, and high water 

temperatures, >80"F (>27"C) can lead to stress and 

subsequent mortality (Blazek 1996). Walleye will 

actively seek pellets at temperatures as low as 40°F 

(4.44"C) (Stevens 1988). 

Dissolved oxygen is a critical parameter in all fish 

culture operations. The dissolved oxygen concentration 

should be measured in the cages on a regular basis. 

Generally, oxygen concentrations of >6 mg/l are best 

for walleye growth. If the oxygen level falls below 3 

mg/l, the fish may become stressed or die. Most oxygen 

in a pond is the result of photosynthesis by aquatic 

plants or phytoplankton. Excess feed or fish waste in 

the pond will act as fertilizer for these plants and can 

cause a rich phytoplankton bloom. The same biomass 

that produced a great deal of oxygen during the day can 

rapidly deplete that oxygen at night when the plants 

become net consumers of oxygen for respiration. The 

lowest oxygen concentration in the daily cycle will 

usually occur just before dawn. Because it is ths lowest 

oxygen concentration that will stress or hll fish, it is 

best to measure oxygen just before sunrise. A downward trend in day-to-day observations of pre-sunrise 

oxygen requires action to prevent a fish kill. Feeding 

should be stopped, or the cage moved to a location with 

higher oxygen concentrations, or aerators should be 

turned on. If a pond has had a rich green color but starts 

to turn brown, the phytoplankton population may be 

dying off. When this occurs, the decomposition of the 

phytoplankton cells coupled with a reduction in oxygen 

production can cause reduced oxygen levels. Feeding 

should be halted during ths time and aerators should be 

started. 

Photosynthesis in a fertile pond affects pH because the 

plant cells take up carbon &oxide as a carbon source, 

and release oxygen. High pH can stress fish, and in 

some cases can cause mortality (Bergerhouse 1992). 

Treatment of the pond with herbicides can lower the pH 

by limiting photosynthesis, but it may also cause an 

oxygen decline due to decomposing vegetation. The 

best way to control pH is to limit nutrient input and 

control vegetation and plankton levels before they reach 

problematic levels. In general, the pH in culture ponds 

should be maintained between 6.5-9. 

Ammonia is the major nitrogenous waste product 

excreted by fish. Ammonia occurs in two forms in 

aqueous solution; the ionized form (NH4+), which is 

essentially non-toxic, and the un-ionized form (NH,) 

which is highly toxic. As pH and temperature increase, 

the proportion of ammonia in the toxic un-ionized form 

increases. In normal cage culture operations where the 

capacity of the pond to metabolize fish waste is not 

overloaded, ammonia should not be a problem. However, if the pond is overstocked or is subject to runoff of 

livestock waste or agricultural runoff, high ammonia 

concentrations can occur causing gill damage, reduced 

growth, or mortality. Un-ionized ammonia concentrations of 0.06 to 0.1 mg/l can stress fish. 

Most cages used for fish culture should have a cover to 

keep predators out of the cage. A solid cage cover is 

preferable to a mesh covering due to the added benefit 

of providmg shade for the fish. Walleye appear to prefer 

shaded or low light environments. 

Aeration in or around a cage can help maintain adequate oxygen concentrations, dissipate supersaturated 

gases, and flush waste from the cage. Providing 

aeration with a blower and airstones may be the best 

way to provide aeration to a large number of cages. In 

addition, this sort of aeration can be used to circulate 

water during the winter, bringing warm water up to the 

surface and preventing the cages from freezing over. 

Ponds will develop thermal stratification both summer 

and winter. Stratified ponds have a warm upper layer, a 

middle zone of rapid temperature change (thermocline), 

and a lower stagnated zone. Water below the thermocline may have very low oxygen and high ammonia, 

hydrogen sulfide, and carbon dioxide. Care must be 

taken that the aerator does not circulate this water from 

the pond bottom as that water may have a large oxygen 

demand. 

257 NCRAC Culture Series 101 -Walleye Culture Manual 
Cleaning and maintenance 

Biofouling by algae or bryozoans on the mesh of the 

cage will restrict the movement of water through the 

cage. If the cages are not cleaned regularly the water 

quality within the cage can deteriorate rapidly, and the 

fish can become stressed. Harder and Summerfelt 

(1996) found it necessary to clean cages 1-2 times per 

week. They used a long handled brush on the inside of 

the cage, and used a snorkel and a hand brush to clean 

the outside of the cage. Stevens (I 996) recommended 

cleaning once per month. He also used brushes and 

snorkel equipment, but in addition he would use a water 

jet to blast the cages clean. Bushman (1996) noted that 

circular cages were more difficult to clean with a brush 

since the sides of the cage were not as well supported. 

Two advantages to grading fish and transferring them to 

cages of larger mesh size as they grow are that the 

larger mesh size will be less likely to become blocked, 

and it will take longer for filamentous algae to become 

established on the new cage. 

Disease control and treatment 

The best method of hsease control is prevention. 

Disease prevention consists of acquiring fish in good 

conhtion and minimizing stress and handling. Activity 

around a cage should be minimized to avoid stressing 

the fish. High water quality must be maintained. When 

fish are handled or hauled, they should be hauled in a 

0.5%-1% salt solution to minimize osmotic stress. Even 

with the best efforts there is the possibility that a 

dsease outbreak will occur. Walleye in cages are 

difficult to treat effectively. Harder and Summerfelt 

(1 996) found that medicated feed (oxytetracycline) 

given as a prophylactic treatment was not effective. 

They resorted to netting the fish out of the cage and 

giving them a dip treatment of a chemotheraputant. 

Currently, however, no drug, chemical, or pesticide is 

approved by the FDA for use in walleye culture. When 

fish are stressed they often stop feeding, making 

medicated feed ineffective. Other species have been 

treated by surroundmg the cage with a plastic enclosure 

to isolate it from the rest of the pond (Kleinholz and 

Luker 1994). However, it is important to remember that 

the plastic isolates the cage from its source of oxygen, 

and supplemental oxygen may be needed during the 

treatment. 

Survival, growth and feed conversion 

walleye survival in cages has varied from 6.5% 

(Harder and Summerfelt 1996) to 93% (Bushman 

1996). However, the case studies in this volume 

demonstrate that good survival can be achieved in cages 

under the right circumstances. Walleye in cages at four 

sites in Minnesota had survival rates ranging from 0- 

61.2% after two growing seasons (Mittelmark and 

Kapuscinslu 1993). 

Walleye have also demonstrated reasonable growth in 

cages. Stevens (1996) reported that walleye reached 

approximately 8 in (203 mm) by the end of the first 

growing season, 12-14 in (305-356 mm) by the end of 

the second growing season, and a market size of 1.5-2 

lb (681-908 g) by the middle of the third growing 

season. Mittelmark and Kapuscinski (1 993) were able 

to get only a portion of their walleye to marketable size 

in three growing seasons (two seasons in the cages). As 

feed quality improves, it is possible that this market size 

could be achieved in the second season. Bushman 

(1996) reported feed conversions of 8.0 for 2.4-in (61- 

mm) walleye, and 4.4 for 5.6-in (142-mm) walleye. 

However, the fish may have been overfed. 

Over-wintering 

An important consideration in the development of a 

commercial walleye cage culture enterprise for production of food-size fish is the need to over-winter walleye 

in cages. When walleye are over-wintered in cages, it is 

necessary to keep the area of the pond around the cages 

free of ice. This is necessary to allow winter feeding, 

allow water circulation through the cage, and to prevent 

damage to the cage from ice scouring. There are a 

number of aeration devices available designed to keep 

ponds from freezing over during the winter. They all 

operate on the same basic principle, which is to bring 

warmer water from the bottom of the pond to the 

surface. Airstones and a blower do an adequate job of 

circulating the water to the surface (Bushman 1996; 

Stevens 1996). 

Winter feedmg is important to increase survival and to 

avoid cannibalism. Stevens (1996) recommended 

feeding walleye over-winter at a rate of 0.5% of their 

body weight per day. Bushman (1996) fed walleye over 

winter at 1 % of their body weight per day. He reported 

up to 98.5% survival of 6-in (152-mm) fish from 

November to April. He also reported a slight weight 

258 NCRAC Culture Series 101- Walleye Culture Manual 
loss in 6-in (152-mm) walleye 

over the winter, but a slight 

weight gain in 3-in (76-mmj 

walleye over the same time 

period. 

Environmental concerns 

Cage culture may have 

environment impacts. Wastes 

from cage culture are normally 

released directly into the 

environment without any lund 

of treatment. Overloading a 

water body’s capacity to deal 

with fish waste will have 

negative effects on both the 

caged fish, the native biota, 

and other uses. If cage culture 

is undertaken in public waters, 

Figure 2. Caillouet floating raceway system, Mid-Continental Fisheries, Marion, 

IL. Airlift pumps are used to circulate water through each raceway. 

the excess nutrients could degrade water quality of that 

lake or stream. Nutrient rich water discharged from a 

constructed pond or lake may alter the nature of a 

receiving stream. 

Some work has been done to reduce the waste released 

from cage culture (Lewis and Wehr 1976)’ but these 

techniques are not in general use. A floating raceway 

system (Figure 2) has a collection box for solid waste, 

References 

Anderson, M., and G. Budiselich. 1991. Cage culture of 

walleye in southern Iowa farm ponds. Pages 68-70 in 

Coolwater fish culture workshop minutes, January 

7-9, 1991 , Springfield, Missouri. 

Bergerhouse, D. L., 1992. Lethal effects of elevated pH 

and ammonia on early life stages of walleye. North 

American Journal of Fisheries Management 12:356- 

366. 

but Qssolved solids (inorganic phosphorus j are released 

into the pond. The best way to avoid environmental 

degradation is careful site selection and to size the 

operation well within the regeneration capacity of the 

water body. 

Blazek, K., 1996. Cage culture of walleye at Mormon 

Trail Lake Iowa. Pages 275-276 in R. C. Summerfelt, 

editor. Walleye culture manual. NCRAC Culture 

Series 101. North Central Regional Aquaculture 

Center Publications Office, Iowa State University, 

Summary 

Cage culture has the potential to contribute to the 

development of walleye as a commercial species. The 

low initial cost of cage construction and use of existing 

water bodies are attractive to walleye culture. Walleye 

can be successfully trained, fed, over-wintered, and 

grown to food size in cages. Procurement of trained fish 

early in the first season, stress and dnease control, and 

high quality but practical feed formulations are all 

important factors in the development of a successful 

and economically viable walleye cage culture 

enterprise . 

Ames. 

Brugge, G. T., and D. J. McQueen. 1991. In situ enclosure culture of walleye. Progressive Fish-Culturist 

53191 -94. 

Bushman, R. P. 1996. Cage culture of walleye and 

walleye x sauger hybrids. Pages 261-266 in R. C. 

Summerfelt, editor. Walleye culture manual. NCRAC 

Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, 

Ames. 

Buttner, J. K. 1989. Culture of fingerling walleye in 

earthen ponds. State of the art 1989. Aquaculture 

Magazine 15(2):37-46. 

NCRAC Culture Series 101 - Walleye Culture Manual 259 
Harder, T. 1992. Use of tanks and cages to train pondreared walleye fingerlings to accept a commercial 

feed. Pages 23-30 in Coolwater fish culture workshop 

minutes, January 6-8, 1992, Carbondale, Illinois. 

Harder, T., and R. C. Summerfelt. 1991. Training pondreared walleye fingerlings in cages to accept formulated feed. Pages 167-1 79 in Coolwater fish culture 

workshop minutes, January 7-9, 1991, Springfield, 

Missouri. 

Harder, T., and R. C. Summerfelt. 1996. Training walleye 

to formulated feed in cages. Pages 267-271 in R. C. 

Summerfelt, editor. Walleye culture manual. NCRAC 

Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, 

Ames. 

Harding, L. M., C. I? Clouse, R. C. Summerfelt and J. E. 

Morris. 1992. Pond culture of walleye fingerlings. 

North Central Regional Aquaculture Center Fact 

Sheet Series No. 102, Michigan State University, 

East Lansing Michigan. 

Kindschi, G. A., and F. T. Barrows. 1991. Optimal screen 

mesh size for restraining walleye fry. Progressive 

Fish-Culturist 5353-55. 

Kleinholz, C. W., and G. W. Luker. 1994. Evaluation of 

an enclosure for bath treatment of caged fish. Journal 

of Applied Aquaculture 4:71-78. 

Lewis, W. M., and L. W. Wehr. 1976. A fish-rearing 

system incorporating cages, water circulation, and 

sewage removal. Progressive Fish-Culturist 38:78- 

81. 

Martin, R. M., and W. R. Heard. 1987. Floating vertical 

raceways to culture salmon (Oncorhynchus spp.). 

Aquaculture 61 :295-302. 

Masser, M. P., 1988a. Cage culture-site selection and 

water quality. Southern Regional Aquaculture Center 

Publication No. 161. Stoneville, Mississippi. 

Masser, M. P., 1988b. Cage culture-cage construction 

and place me nt. Southern Regional Aquaculture 

Center Publication No. 162. Stoneville, Mississippi. 

McKee, D. A., M. T. Ordner, D. Houston, and A. 

Lawrence. 1989. Easily constructed, inexpensive 

cage for aquatic animals. Progressive Fish-Culturist 

51 11 66-1 67. 

Mittelmark, J., and A. Kapuscinski. 1993. Walleye 

culture in Minnesota. Minnesota Sea Grant, St. Paul, 

Minnesota. 

Moore, A., M.A. Prange, B.T. Bristow, and R.C. Summerfelt. 1994a. Evaluation of tank shape and a 

sutface spray for intensive culture of larval walleye 

fed formulated feed. Progressive Fish-Culturist 

56: 100-1 10. 

Moore, A,, M.A. Prange, B.T. Bristow, and R.C. 

Summerfelt. 1994b. Influence of stocking densities on 

walleye fry viability in experimental and production 

tanks. Progress Fish-Culturist 56: 194-201 . 

Mortensen, S., 1987. Reliable and inexpensive fish 

feeder. In Coolwater fish culture workshop minutes, 

January 4-6, 1987, Albia, Iowa. 

Selock, D., 1990. Site selection and water quality: 

success or failure in cage culture. Pages 10-12 in D. 

L. Swann and P. B. Brown, editors. Midwest Regional 

Cage Fish Culture Workshop, August 24-25, 1990, 

Jasper, Indiana. 

Stevens, C., 1988. Overwintering walleye: 1986 season. 

In Coolwater fish culture workshop minutes, January 

4-7, Aberdeen, South Dakota. 

Stevens, C., 1996. Cage culture of walleye and its 

hybrids to food size. Pages 273-274 in R. C. Summerfelt, editor. Walleye culture manual. NCRAC 

Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, 

Ames. 

Summetfelt, R.C., C.P. Clouse, and L.M. Harding. 1994. 

Pond production of fingerling walleye, Stizostediun 

vitreum, in the northern great plains. Journal of 

Applied Aquaculture 2:33-58. 

Swann, D. L., 1990. Cage construction “round or 

square?” Pages 35-46 in D. L. Swann and P B. 

Grown, editors. Midwest regional cage fish culture 

workshop, August 24-25, 1990, Jasper, Indiana. 

Swann, L., J. Morris, D. Selock and J. Riepe. 1994. 

Cage culture of fish in the North Central Region. 

North Central Regional Aquaculture Center Fact 

Sheet Series No. 110, Iowa State University, Ames 

Iowa. 

Westers, H., and R.R. Stickney. 1993. Northern pike and 

muskellunge. Pages 199-21 3 in R.R. Stickney, editor. 

Culture of nonsalmonid freshwater fishes, 2nd 

edition. CRC Press, Boca Raton, Florida. 

260 NCRAC Culture Series 101- Walleye Culture Manual 
Bushman, R. I? 1996. Cage culture of walleye and walleye x sauger hybrids. Pages 261-266 in R. 

C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North Central 

Regional Aquaculture Center Publications Office, Iowa State University, Ames. 

Cage Culture of Walleye and Walleye x 

Sauger Hybrids 

Richard P Bushman’, Resource Conservation and Development for Northeast Iowa, Inc., PO. Box 348, 

Postville, Iowa 52 162 

Introduction 

Resource Conservation and Development for Northeast Iowa, Inc. (RC&D) initiated a project in the fall of 

1992 to evaluate the potential for coolwater food fish 

production in northeast IA farm ponds to provide 

supplemental income to pond owners. Because most 

farm ponds are not seinable or drainable, cage culture 

was selected as the culture method. Walleye and hybrid 

walleye (walleye x sauger) were chosen because of 

their reputation as a lugh quality food fish and compatibility of these fish species for the climate in northeast 

IA. The objectives of this project were to develop 

recommendations for the utilization of northeast Iowa 

farm ponds for culturing food fish species for sale as 

food fish and to educate pond owners of the benefits of 

aquaculture as an addtional form of agriculture. 

long; 10 pieces, 43.7 in (1 11.1 cm) long; 8 pieces, 44.7 

in (113.7 cm) long ; 8, 3 way elbows; 4, 4 way elbows; 

4, tees. 

High density polyethylene netting was used for the 

bottom and the sides of the cages. The netting was 

secured to the PVC pipe with 8 in (20.3 cm) UV 

resistant cable ties. The mesh size used on the cages 

was determined by the size of the fish at stochng: 0.25 

in (0.6 cm) mesh was used for 2.0-3.0 in (50.8-76.2 

mm) fish and 0.5 in (12.7 mm) mesh was used for 4.0- 

5.0 in (101.6-127.0 mm) fish. One 4.5 ft (1.3 m) long 

6.0 in (1 5.2 cm) PVC pipe was capped at each end and 

was secured to each end of the rectangular cages with 

1.5 in (3.8 cm) U-bolts and 28.3 in (71.8 cm) long UV 

resistant cable ties. These were used as floats to keep 

pieces, 20.8 in (53.0 cm) 

Figure 1. Rectangular cage diagram; timers (T) were placed on dock (not shown). 

Present address: Illinois Department of Natural Resources, 2649 N 21st Rd, Marseilles. IL 61344 

261 NCRAC Culture Series 101 - Walleye Culture Manual 
Chapter 10 - Cage Culture of Walleye 

12 volt DC 

8 x 0.75 in gear motor 

wood screws 

2.5 in x 1.25 in 

metal corner irons 

8 x 0.75 in 

wood screws 

8 x 0.75 in 

wood screws 

0.31 in dia. n 

brake line tubing 

13.0 in x 0.1 9 in 

threaded rod 

8 x 0.75 in 

wood screws 

~ 1.0 in x 0 10 in 

cotter pins 

1l 12.0 in x 6.0 in 

-4 ~ 8 x 0.75 in 

wood screw 

scraper 

metal drive cleat 

10x24 

6.9 in dia. 

metal plate 

wing nut 

hex nut no. 10 

lock washer 

no. 10 

10x24 lock washer 

Figure 2. Rotating disk feeder. 

the top of the cage about 4 in 

(1 0.1 cm) above the water 

surface. At the waterline, the 

capacity of the cages was 117.4 

ft" (3.3 m". 

To evaluate different cage 

designs, an addtional cylindrical cage (4.0 x 4.0 ft, 1.2 x 1.2 

m) was placed in the pond. The 

frame for the cylindrical cage 

was constructed of 0.75 in (1.9 

cm) black plastic tubing and 

four pieces of 4.0 ft (1.2 m) 

long, 2.0 x 2.0 in (5.1 x 5.1 cm) 

lumber for vertical supports. A 

square collar constructed of 2.0 

in (5.1 cm) PVC pipe was used 

to keep the top of the cylindncal cage about 4.0 in (1 0.1 cm) 

above the water surface. There was 46.0 ft3 (1.3 

m3) of water in ths cage. 

Cage lids were constructed of 0.5 in (I .2 cm) 

plywood. The rectangular cage lids were hinged 

using two 6.0 in (15.2 cm) long x 2.0 in PVC pipe 

and four 1.5 in (3.8 cm) long x 0.5 in (1.3 cm) 

carriage bolts. Two 2.0 in (5.1 cm) flat hinges 

were used on the cylindrical cage lids, which 

allowed one-half of the lid to be opened. The 

cages were secured with nylon rope to floating 

docks constructed from used oak pallets (40.0 x 

48.0 in, 101.6 x 121.9 cm) and 55.0 gal (208 L) 

plastic barrels. 

Feed e rs 

Two rotating &sk style feeders (Figure 2) were 

fastened to the rectangular cage lids, and one 

feeder was fastened to the cylindncal cage lid 

using 2.0 in (5.1 cm) corner irons. The feeders we 

used were originally described by Steve 

Mortensen (1 987 Coolwater Fish Culture Workshop). The feeder motor was a 12 V DC, 40 rpm, 

reversible gear motor (Barber Colman, Rockford, 

IL). Each feeder was fastened to and covered with 

a 5.0 gal (18.9 L) plastic bucket. The feeding 

regimen was controlled at the ponds using 12 V 

Figure 3. Cage culture setup on pond in northeast Iowa showing cages tethered 

to T-shaped floating dock. White buckets provide protection for feeders on 

cages. 

262 NCRAC Culture Series 101- Walleye Culture Manual 
Cage Culture of Walleye - Chapter 10 

timers (DFT1 -Q, Sweeney Enterprises, Boerne, TX). 

The power supply was a 12 V garden tractor battery, 

and the feeders were connected to the timers using 12 

gauge two-stranded wire. The timers and battery were 

placed on the dock, underneath a 5 gal (18.9 L) bucket 

for protection from rain (Figure 3). 

Fish stocking 

On July 19, 1993, fingerling hybrids were obtained 

from the University of Wisconsin Aquaculture Center, 

Madison, WI and stocked into cages in the 4.0 acre (1.6 

ha) pond (Table 1). On August 5, 1993 and August 30, 

1993, fingerling walleye were obtained from Iowa State 

University, Ames, IA and stocked into cages in the 1.2 

acre (0.5 ha) pond. All fingerlings obtained for this 

project had been trained in tanks to consume formulated 

feed. 

Fingerlings were transported in a 200 gal (757 L) 

hauling tank supplied with oxygen at a rate of 1-2 L/ 

min. Salt was added to provide a 0.5-0.7% concentration, and ice was added to the tank to maintain the 

water temperature at 68.0-72.0"F (20.0-22.2"C) during 

the 3-4 h trips. 

Upon arrival at the cage site, the fish were tempered 

with enough water to cause a 2°F (3.6"C) temperature 

change every 30 min. As the fish were being tempered, 

a sample of 50-70 

fish were measured 

to the nearest 

millimeter (TL) and 

weighed to the 

nearest gram. The 

number of fish in 

one pound was then 

determined. 

Each cage was 

stocked by weighing groups of 

fingerlings in a 5 

gal (18.9 L) bucket 

suspended from a 

20 lb (9.0 kg) 

(Table 1). In the 1.2 acre (0.48 ha) pond, one cage was 

stocked with 580 fish and the other cage was stocked 

with 508 fish. 

A sample of 20-25 fish was sampled from each cage at 

2 week intervals during the growing season. The fish 

were measured to the nearest millimeter and weighed to 

the nearest gram. Condtion factor (K) was also 

calculated, K = (weight /TL') x lo5, where weight in g, 

and TL in mm. 

Feeding 

Feeding began on the day after the fish were stocked. 

The feeding rate for each cage was calculated using the 

following formula: daily ration = (initial number of fish 

- cumulative moralities) x mean weight x percentage of 

body weight to feed. In July and August, the feedmg 

rate was 7.0%, in September, the feedmg rate was 4.0- 

5.0%, and in October, the feedmg rate was 2.0-3.0%. 

The feeding rate from November through April was 

1 .O% body weight/d. 

The timers were set to feed every 15 min during the 

growing season. This feedmg regimen was maintained 

until water temperatures decreased to 60" F (15.6" C). 

At that point, the timers were set to feed once every 15 

min from 0600-0830 and from 1700-1 930 during 

September and October. Over the winter, timers were 

Table 1. Fingerling stocking by cage for hybrid 

walleye and walleye. 

Stocking Fish Cage Mean Mean Number Stocking 

date shape' length weight per cage density 

(in) (no/lb) (n o/f t3) 

7/19/93 Hybrid R 2.5 215.9 822 7.0 

7/19/93 Hybrid C 2.5 215.9 358 7.8 

8/5/93 Walleye R 2.4 197.5 580 4.9 

8/30/93 Walleye R 5.6 22.3 508 4.3 

R = rectangular cage, C = cylindrical cage. 

set to feed three times/ 

d: at 0800, 1200, and 

1700. 

Fingerling hybrids 

were initially fed 

number 3 crumble 

Walleye Grower 9015 

(Murray Elevators, 

Murray, UT). Feed 

size was gradually 

increased to a %Z 

pellet (Silver Cup 

Salmon, Murray 

Elevators, Murray, 

UT) by November. 

The fingerling walleye 

hanging scale. The bucket was filled with 10 lb (4.5 kg) 

of water to zero the scale. The two rectangular cages in 

the 4.0 acre (1.6 ha) pond were stocked with 882 fish/ 

cage, and the cylindncal cage was stocked with 358 fish 

stocked on August 5, were initially fed a mixture of 

25% FFKC formula (Kyowa Hakko Kogyo Co., Ltd, 

Tokyo, Japan) and 75% Walleye Grower, and were 

gradually switched to 100% number 4 crumble Silver 

NCRAC Culture Series 101 - Walleye Culture Manual 263 
Chapter 10 - Cage Culture of Walleye 

Cup Salmon by November. The fingerling walleye 

stocked on August 30, were initially fed % Silver Cup 

Salmon pellets and were gradually switched to '/s Silver 

Cup Salmon pellets by 

November. 

Cage cleaning 

Each cage was cleaned 3 timedweek using a floor 

broom. This prevented algae and fouling from accumulating on the mesh, which decreases water exchange 

between the cage and the pond. 

Water quality 

water temperature and dissolved oxygen profiles were 

taken at least 3 times/week using aYSI DO meter 

(model 51B, YSI Inc., Yellow Springs, OH). Vertical 

profiles of DO in the pond were taken between 0500 h 

and 0700 h, at the water surface, at 4.0 ft (1.2 m), and at 

12.0 ft (3.6 m). Weekly water samples were also 

collected using a Kemmerer bottle lowered 3.0 ft (0.9 

m) inside a different cage each week. These samples 

were analyzed (HACH Kit, FF-2, HACH CO, 

Loveland, CO) for the following parameters: pH, total 

alkalinity, total ammonia nitrogen (TAN), un-ionized 

ammonia (UIA), nitrite-nitrogen, and chloride. Nitratenitrogen and nitrate concentrations were measured 

using a HACH kit (NI-14). During 

July and August, a dnsolved gas 

meter was used to measure dmolved 

gas pressures (percent saturation). 

water circulating through the cages on calm days. 

Throughout the winter, the aerators were used to keep 

the area around the cages ice-free. During periods of 

sub-zero weather, the aerators operated at least 18 h/d 

to maintain a 10-30 ft (3.0-9.0 m) diameter ice-free 

area (Figure 4). During less severe weather, the aerator 

could be operated 12 h/d, which would maintain a 25- 

50 ft (7.5-15.0 m) dmneter ice-free area. 

The fish were not completely harvested in any cage, as 

this is an ongoing project. On September 29, 1993, the 

cages with hybrids were raised from the water, the fish 

weighed, measured and restocked (240 fishkage) into 

cages with 0.5 in (12.7 mm) mesh. The cylindrical cage 

was removed and an additional rectangular cage was 

placed in the pond. On November 8, a sample of 50 

walleyekage were weighed and measured, survival was 

estimated from the number of cumulative moralities to 

date. 

Results 

Survival of the fingerling hybrids raised in the rectangular cages was 33.5%. These fish grew to a mean 

length of 4.9 in (12.4 cm) and averaged 3 1.8 fish/lb 

(14.2 9). Survival of the hybrids stocked in the cylindncal cage was 36.6%. The fish raised in the cylindrical 

cage grew to a mean length of 4.9 in and averaged 36.9 

fisldlb (12.3 g). Survival during the overwinter period 

A 0.5 hp air blower was installed at 

each pond. Air was delivered 

through 0.5 in (12.7 mm) black 

plastic tubing to four, 6.0 in (15.2 

cm) air stones. The air stones were 

connected together on a grid 

constructed from 0.75 in (1.9 cm) 

PVC pipe which was placed about 

18.0 in (45.7 cm) off the pond 

bottom. The air stone grid was 

positioned 20.0-30.0 ft (6.0-9.0 m) 

from the cages. A 115 volt, 24 h 

timer was used to start the blower. 

During the summer, the aerators 

were used to maintain dssolved 

oxygen levels at night and to keep 

..... . >*XI Y 

Figure 4. Winter scene of cage culture in northeast Iowa showing iceclearing effect of aeration apparatus. 

264 NCRAC Culture Series 101- Walleye Culture Manual 
Cage Culture of Walleye - Chapter 10 

was 98.0%, however the fish lost 

weight (Table 2). 

Table 2. Lengths and weights of fish overwintered. 

Survival of the 2.4 in (6.0 cm) 

walleye stocked on August 8, was 

93.0%. The fish grew to a mean 

length of 3.0 in (7.6 cm) and 

Fish Survival Fall Spring Fall Spring Fall Spring 

("3") length length weight weight condition condition 

(in) (in) (no/lb) (no/lb) (K) (K) - 

averaged 132.0 fish/lb (3.4 g) on 

November 8. Survival of the 5.6 Hybrid 34.0 4.9 4.8 31.8 40.9 0.74 0.61 

in (14.2 cm) walleye stocked on Walleye 93.0 3.0 3.1 133.5 116.4 0.77 0.82 

August 30 was 98.0%. These fish Walleye 98.0 6.0 6.1 16.0 17.1 0.80 0.72 

grew to a mean length of 6.0 in 

(15.2 cm) and averaged 16.0 fish/ 

lb (28.3 g) on November 8. 

Table 3. Means (+S.D.) and ranges of water 

quality parameters measured from July 

through October 1993. 

In November, 250 of the 6.0 in (15.2 cm) walleye 

were stocked into a private lake, which reduced the 

density in this cage to 0.1 3 lb/ft3 (2.1 kg/m3). 

Survival over the winter was 96.7% for the 3.0 in 

(7.6 cm) walleye, and 98.5% for the 6.0 in (15.2 cm) 

walleye. The 6 in (15.2 cm) fish lost weight, while 

the 3.0 in (7.6 cm) fish gained weight over the winter 

(Table 2). 

Ponds used for 

Hybrid walleye Walleye 

54.9f10.4 

(34.7-71.6) 

11 -6f2.4 

(7.2-1 5.0) 

7.8fO.l 

(7.8-8 .O) 

307.0f19.1 

(290.0-349.0) 

0.36fO. 12 

(0.20-0.60) 

0.007A0.004 

(0.003-0.01 1) 

0.39A0.20 

(0.00-0.65) 

9.7k6.7 

(4.0-1 7.5) 

2.5k1 .O 

(1 .O-4.0) 

10.9f4.4 

(4.4-1 7.6) 

Parameter 

Temperature (OF) 59.231 1.3 

(35.6-73.4) 

Feed conversion was calculated from the time the 

fish were stocked through the fall sample date. For 

the hybrids reared in the rectangular cages, feed 

conversion was 3.6, and 5.0 for those raised in the 

cylindrical cages. The feed conversion was 8.0 for 

the 2.4 in (3.5 cm) walleye and 4.4 for the 5.6 in 

(14.2 cm) walleye. 

Dissolved Oxygen (mg/L) 14.4fl.4 

(9.2 - 23.5) 

PH 7.9A0.1 

(7.8-8 .O) 

Total Alkalinity 

(mg CaC03/L) 

205.8f24.4 

Average water temperature at a depth of 4 (1 82.0-242.0) ft (1.2 m) 

in the hybrid pond averaged 65.8"F (1 83°C) during 

July, 70.3"F (21 .O"C) in August, and 53.5 OF 

(12.0"C) in October. Dissolved oxygen at the 4 ft 

(1.2 m) level averaged 13.3 mg/L in July and 14.9 

mg/L in October. The means for pH, total alkalinity, 

TAN, UIA, nitrite-nitrogen, chloride, nitratenitrogen, and nitrate were: 7.9, 205.8 mg/L, 0.32 mg/ 

L, 0.012 mgL, 0.01 mgL, 4.9 mg/L, 5.3 mg/L, and 

23.3 mg/L, respectively (Table 3). 

Total Ammonia Nitrogen 

(mg NH3-N/L) 

0.32kO. 20 

(0.00-0.70) 

Un-ionized Ammonia 

(mg NH3/L) 

0.01 2f0.011 

(0.000-0.034) 

Nitrite-Nitrogen (mg/L) 0.01 fO.02 

0.00-0.04) 

Chloride (mg/L) 4.9f2.8 

(1.6-8.3) 

Average water temperature at a depth of 4 ft (1.2 m) 

in the walleye pond was 65.O"F (18.3"C) during 

August, it decreased to 58.O"F (14.4"C) in September, and 50.8"F (10.5"C) in October. Dissolved 

oxygen at the 4 ft (1.2 m) level averaged 8.9 mgL in 

July and 11.4 mg/L in October. The means for pH, 

total alkalinity, TAN, UIA, nitrite-nitrogen, chloride, 

nitrate-nitrogen, and nitrate were 7.8, 307.0 mgL, 

Nit rate-N it roge n (mg/L) 5.3f1.4 

(3.4-7.3) 

Nitrite (mg/L) 23.3A6.3 

(15.0-32.1) 

NCRAC Culture Series 101 - Walleye Culture Manual 265 
Chapter 10 - Cage Culture of Walleye 

0.33 mg NH,-N/L, 0.007 mg NH,/L, 0.39 mg/L, 9.7 

mgL, 2.5 mgL, and 10.9 mgL, respectively 

(Table 3). 

During the summer of 1993 , rainfall was above average 

in northeast Iowa and water quality in the pond with 

hybrids was affected by runoff. After periods of heavy 

rain, the pond was frequently observed to be turbid, 

with visibility less than 6.0 in (15.2 cm). As the ponds 

cleared, algae blooms would occur as nutrients were 

released from the runoff water. 

During algae blooms, dmsolved oxygen readmgs were 

frequently greater than 15.0 mgL, even in the early 

morning. Dissolved gas pressures were monitored when 

D.O. readings exceeded 15.0 mg/L, and the percent 

saturation was nearly 170%. Algacides (copper sulfate 

and Cutrine-plus) were used at 2.04.0 ppm in an 

attempt to control the planktonic algae blooms. Continuous aeration was also found to bring the dissolved 

oxygen level in the pond to saturation. 

The high levels of dissolved gases in the pond had a 

negative effect on fish health, causing mortality during 

a 6 d period (August 24-30). A sample of hybrid 

walleye taken to the Fish Disease Control Center (US. 

Fish and Wildlife Service, Lacrosse, WI) were diagnosed as having gas bubble disease. Gas bubbles were 

found lodged between the fin rays and on the roof of the 

fishes mouth. Also, microscopic examination revealed 

small embolisms on the dntal ends of the gill filaments. 

No signs of bacterial infection were found. The 

dissolved gas levels eventually decreased in the ponds, 

and moralities ceased. 

Discussion 

There are many obstacles to overcome before cage 

culture of a coolwater fish species is successful in 

northeast Iowa farm ponds. Hybrid walleye had an 

average growth rate of 0.16 g/d and 0.83 mm/d. 

Although survival over the winter period was high, 

some fish lost weight. There was little difference in 

growth between hybrids raised in the cylindncal and 

rectangular cages. The only noticeable difference in 

performance between the two cage designs was that the 

cylindncal cage was more difficult to keep clean with a 

floor broom, as there was not enough support on the 

side of the cage to keep it rigid during cleaning. 

In addtion to the hgh gas pressures experienced in the 

pond used to rear hybrids, cannibalism may have 

contributed to low survival of hybrids. When the cages 

were raised and the fish were counted in the fall, 2-3 

fish were found in each cage that were 2.0-3.0 in longer 

than the average fish in the cage even though cannibals 

that were seen as the fish were being stocked in July 

had been removed. However, either some cannibals 

must have been stocked initially, or some of the trained 

fingerlings did not accept the diet we were using and 

reverted back to a fish diet. 

Fingerling walleye had growth rates of 0.18-0.22 mdd 

and 0.01-0.16 g/d, much slower than hybrid walleye. 

The slow growth of the fish in the walleye pond was 

probably due to low water temperatures, which were 

typically less than 70°F (21.1 "C). The relatively high 

survival rate of these fish was due to good condition of 

the fish at stochng and a high quality culture environment. 

Cage culture allows existing ponds and lakes to be 

utilized for fish production. Fish can easily be harvested, and sport fishing can be continued in the ponds. 

However, cages require daily cleaning to remove algae, 

organic matter, or other attached growth, which may 

accumulate on the mesh and reduce water exchange. 

Also, caged fish cannot move to different areas of the 

pond if water quality deteriorates. When water quality 

is poor, the resulting stress on the fish may predispose 

them to disease. 

Feed trained fingerlings for this project could not be 

obtained from commercial sources, so fingerling 

availability is a major problem for potential growers. 

Due to the short growing season in northeast IA, it will 

take at least 2, but probably 3 years to raise a coolwater 

fish to marketable size. The long time to reach market 

size will probably make cage culturing of walleye or 

hybrid walleye to food size unprofitable in pond 

environments at similar latitudes. 

266 NCRAC Culture Series 101- Walleye Culture Manual 
Harder, T., and R. C. Summerfelt 1996. Training walleye to accept formulated feed in cages. Pages 

267-271 in R. C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North 

Central Regional Aquaculture Center Publications Office, Iowa State University, Ames. 

Training Walleye to Formulated Feed in 

Cages 

Tom Harder, Max McGraw Wildlife Foundation, PO. Box 9, Rundee, lL 601 18 and Robert C. Summerfelt, 

Rept. of Animal Ecology; Iowa State University, Ames, IA 500 1 1-322 I 

Introduction 

Cage culture is an alternate method for 

raising fish when ponds or raceways 

(tanks) are not available. Cage culture 

may be appropriate for producing 6-in 

(15 cm) fingerlings for stochng lakes or 

as a “starter” size for commercial farms 

which grow walleye to food size. The 

objective of this project was to develop 

techniques for training 2-in (5-cm) 

pond-raised fingerlings to accept 

commercial feed in cages and to raise 

feed-trained walleye to a target size of 6 

in (1 5 cm) by the fall of their first 

summer. Although cage culture has been 

studied in several other species of fish, 

in 1989 when this project was initiated, 

there were no reports dealing with cage 

culture of walleye. 

Methods 

Cages 

Cages were located in a 30-acre (12.1- 

ha) reclaimed limestone quarry lake in 

northeastern Illinois on the property of 

the Max McGraw Wildlife Foundation. 

The cage site was at the east end of the 

lake where the cages were partially 

protected from strong westerly winds by 

a peninsula, but the location still had 

exposure to sufficient wave action to 

Figure 1. The floating 8-ft x 8-ft (2.4-m x 2.4-m) raft to which six cages 

were tethered. Other components are: 12 volt deep cycle battery; 

timers; RPM control boxes; hinged sheet-metal lids; and feeders. 

L 

furnish a satisfactory water exchange through the cages. 

Water depth beneath the cages was 22 ft (6.7 m). 

Six cages were attached to a floating 8-ft x 8-ft (2.4-m x 

2.4-m) raft. The deck of the raft was constructed from 

treated lumber. The raft had seven 4-ft-long (1 .2-m) 

extensions radiating outwards, and the cages were 

attached to these extensions (Figure 1). 

Cylindncal4-ft-diameter x 4-ft deep (1.2 m x 1.2 m) 

cages were constructed from two 4-ft-dameter (1.2-m) 

hoops made from 13-ft (3.9-m) pieces of 0.75-in (19- 

NCRAC Culture Series 101 - Walleye Culture Manual 267 
Chapter 10 - Cage Culture of Walleye 

mm) diameter black plastic tubing (Figure 2). The cage 

frames were covered with 0.25-in (6-mm) &amondmesh black plastic. Six 4-ft (1 -2-m) pieces of 0.75-in 

(19-mm) PVC pipe connected the top and bottom hoops 

to make the cages rigid. The edges of the mesh cylinder 

were laced to the hoops with bell-wire. Mesh along the 

cylinder sides was overlapped by about 6 in (150 mm) 

and double-laced. To keep feed from falling through the 

bottom of the cage and to allow visual assessment of 

feed accumulation, plastic garbage can lids were 

fastened to the inside bottom of each cage. The cage lid 

was light-weight galvanized sheet metal. Holes were 

cut in the lid to accommodate feeders, and half the lid 

was hinged to provide for cage access. The lid was 

\ 

attached to the cage using plastic cable ties. In 1989, 

materials used to build the cages cost $85 per cage. 

Cages were made buoyant by attaching 1.5-in (38-mm) 

slotted foam pipe insulation around the cage 12 in (30.5 

cm) below the lid. Water volume in each cage was 44 ft3 

(1.24 m3). The foam insulation was not sufficiently 

buoyant to support the cages when wild ducks used the 

cage lid as a resting site. To keep ducks off the cages, 

3-in (7.6 cm) mesh bird netting was draped across the 

cages and over their sides to water level. 

Cages were cleaned once or twice a week to remove 

filamentous algae. Cages were cleaned on the inside by 

using a long-handled brush and on the outside by handbrushing while swimming around the cage. 

Feeders 

In the first year (1989), we made the feeders from a 

design by Steve Mortensen (see illustration in case 

study by Bushman [ 19961). Mortensen’s (1 987) design 

used a rotating disc mounted under a piece of PVC 

pipe. A small DC motor rotated the disk. Feed was 

dispensed in a uniform pattern out from the center of 

the cage; however, these feeders were dfficult to 

calibrate, they jammed when the feed got wet, and 

sometimes the electrical connections between feeders 

and control boxes shorted out. Because of these 

problems, in 1990 and 1991, commercial vibrator 

feeders were used (model AF7, Sweeney Enterprises, 

Boerne, TX). 

The power system for the feeders was a single 12-v 

deep-cycle battery. This was wired to two electrical 

timers (Sweeney model DFTl Q). Each timer was able 

to turn on the feeders twice per hour. To obtain four 

feedings per hour, the two timers were wired in series 

and their trip levers set so that the feeders would go off 

four times each hour, 17 h/d. Each feeder was controlled by an electrical power source (Sweeney SE-70D 

RPM) that regulated the intensity of vibration of the 

feeder. The amount of feed dispensed each day was 

regulated by feeding frequency, by adjusting the gap 

above the feeder plate, and by adjusting the intensity of 

vibration. 

Figure 2. A 44-ft3 (1.24-m3) plastic mesh cage with 6-in 

(150 mm) seine floats (replaced by a foam ring) for 

flotation; sheet-metal lid; PVC cover for feeder (used 

the first year only); top and bottom support rings; PVC 

upright supports. 

In 1989, one feeder was located on the center of each 

cage. However, we found that walleye spent most of 

their time cruising the cage perimeter where they would 

be less likely to see the sinking feed. Therefore, in 1990 

268 NCRAC Culture Series 101- Walleye Culture Manual 
Cage Culture of Walleye - Chapter 10 

and 1991, two or three feeders were used for each cage 

to ensure that the fingerlings encountered the falling 

feed. 

Feed and Feeding 

In 1989, as a prophylactic measure, a medcated 

(oxytetracycline) feed formulation of the W- 16 diet 

(Balshi, Inc., Catawissa, PA) was used to cage-train 

walleye in groups 1 and 2. This feed was hard, it had 

sharp edges, and sank quickly. Feed size was initially 

number 3 granules; but as the fish grew, the feed size 

was increased to granule number 4, and then to %-in 

(2.3-mm). In 1989, cost of the W-16 det was about 

$0.45/lb ($0.99/kg) delivered. In 1990, fish were started 

on a medicated 4 Biotrainer feed (Bioproducts, 

Warrenton, OR), followed by number 5 Biotrainer, then 

1.5-mm Biodry 4000. The Biotrainer formulations were 

semi-moist crumbles, and they were slower sinhng 

than the W-16 feed. The delivered cost of Biotrainer 

was $5.94/lb ($13.06/kg) and of Biodry 4000 was 

$l.OO/lb ($2.21/kg). The feed was expensive because 

small quantities were ordered and it was shipped by 

parcel delivery service rather than common freight. In 

1992, group 4 was also fed Bioproduct feed up to 1.5- 

mm pellet size, but they were finished on locally 

available trout feed (Purina 5104 crumble; Purina, St. 

Louis, MO) which cost $0.44/lb ($0.97/kg). 

During cage training, feeding rates were initially 18- 

20% of total body weight/day. This was well above the 

6-8% feeding rates used to train walleye in tanks 

(Kuipers and Summerfelt 1994); however, the higher 

rate was used to compensate for feed loss through the 

cage. The high initial feeding rate was reduced to 6- 

10% as the fish were habituated to the feed and as they 

grew. Periodic length and weight measurements were 

taken and daily mortalities monitored to maintain an 

inventory, which was needed to determine the amount 

of feed to add. 

Water qualify 

During the three growing seasons, water temperatures 

ranged from 68 to 79°F (20 to 26°C). Dissolved oxygen 

ranged from 7 to 10 ppm. Secchi dsc visibility was 14 

to 20 ft (4.3 to 6.1 m). Alkalinity ranged 300 to 400 

ppm as CaCO,, which is high but typical of limestone 

quarry lakes. 

Fish 

Four groups of walleye were cultured in cages between 

1989 and 1991 : groups 1 and 2 in 1989, group 3 in 

1990, and group 4 in 1991. Fingerlings were purchased 

from sources in Wisconsin and Iowa. Fish were 

transported in 0.5% salt solution. At the lake, fish were 

tempered by pumping lake water into the hauling tank. 

Only group 4 was feed-trained prior to stochng. At 

stocking, fingerlings ranged from 1.8 to 2.7 in (46 to 70 

mm). Initial stocking densities for group 1 were 10 and 

20 fish/ft3 (350 or 700/m3) (440 and 880 fish per cage) 

(Table 1). Fish in group 2 were stocked into two cages 

on August 24 at a density of 23 fisldft’ (805/m3). To 

avoid the high mortality experienced with group 1, 

handling was kept to a minimum. Water temperature at 

stocking was 75°F (24°C). Group 3 walleye were 

stocked into two cages on July 29. Handling was kept to 

a minimum. Each cage was provided with three feeders. 

Stoclung density was 5 1 fish/ft3 (1 ,250/m3). Water 

temperature was 72°F (22°C). In 1991, group 4 walleye 

were tank-trained to formulated feed prior to stocking. 

These walleye were stocked into three cages on July 25 

when water temperature was 77°F (25°C) which was at 

least 2°F warmer than these temperatures at the time of 

stochng of the previous groups in 1989 and 1990. Fish 

were stocked at 11 fish/ft3 (385/m3) or 484/ cage. 

Resu Its 

In 1989, about 76% of the first group of fish died 

within 6 days of stochng. Handling fingerlings to 

obtain lengths and weights contributed to this problem, 

but it seemed that the major factor was the fact that the 

producer had held the fish in tanks without feeding for 

several days prior to transport. On arrival, the fish were 

emaciated and showed clinical signs of columnaris. 

Water temperature was 73°F (23°C) when they were 

stocked on July 24. After the sixth day, the 960 survivors were consolidated into three cages. Survival of 

these fish to 105 days was 27% (Table 1). 

Group 1 grew from an average stocking weight of 1.7 g 

(267 fisMb; 587kg) to 14.2 g (32 fisMb; 70 fishkg) 

over 105 d. Their specific growth rate (percentage of 

body weight gain per day) was 2.02%. They averaged 

5.1 in (131 mm) at harvest (Table 1). Density at harvest 

was 6 fish/ft3 (210/m3) or 260 fish per cage. 

There were no mortalities in group 2 fish until the fifth 

day after stocking. They grew from 2.1 in (53.3 mm) to 

NCRAC Culture Series 101 - Walleye Culture Manual 269 
Chapter 10 - Cage Culture of Walleye 

3.9 in (99.1 mm) in 76 d in cage culture (0.6 mdd). 

Weight gain was 2.1 g (216 fish/lb; 476kg) to 8.7 g (52 

fish/lb; 114kg). Their specific growth rate was 1.87%, 

the lowest of all four groups. Finished density was 6 

fish/ft3 (210/m3), the same as that of group 1. Survival 

was 13.5%. survival doubled. 

30.3 g (15 fisMb; 33ikg) in 105 d and averaged 6.2 to 

6.3 in (157 to 159 mm) at harvest. Survival was 22 to 

23%. At harvesting, density averaged 11 and 12 fish/ft" 

(385-420/m3) (Table 1). Although stocking density for 

group 3 was 2.2 times greater than for group 2 (1990), 

In 1990 (group 3) mortalities were low until day 9. Fish 

in group 3 grew from 0.8 g (568 fish/lb; 125Okg) to 

In 1991, the average survival to 79 d was 85.6% (Table 

1). Fish grew from 168 fish/lb (370kg) to 19 fish/lb 

Table 1. Summary of stocking and harvest data for walleye cage (44 ft3; 1.25 m3) culture field 

trials at the Max McGraw Wildlife Foundation, 1989-1 991. 

Initial Finall 

Year Cage Fish/ Fish/ft3 Fish/lb Mean Survival Fish/ft3 Fish/lb Mean Mean 

(group) (stocking Cage (fish/ m3) (fish/ kg) weight (?/) (fish/m3) (fish/ kg) weight length 

date) (9) (9) (mm) 

1,293 

(7/24) 

4,536 

(7/24) 

1 

(8/24) 

2 

1 

2 

1 

2 

3 

440 

880 

1,012 

1,012 

2,250 

2,250 

51 0 

51 0 

51 0 

267 

(587) 

267 

(587) 

21 6 

(476) 

(476) 

21 6 

568 

(1,250) 

(1,250) 

568 

168 

(370) 

(370) 

(370) 

168 

168 

1.7 

1.7 

2.1 

2.1 

0.8 

0.8 

2.7 

2.7 

2.7 

260 

(6.5) 

258 

(1 3.5) 

506 

(22.5) 

51 9 

(23.1 ) 

425 

(83.3) 

494 

(96.9) 

390 

(76.5) 

32 

(70) 

52 

(114) 

15 

(33) 

(34) 

16 

19 

(42) 

(46) 

(37) 

21 

17 

14.2 

(0. i2)4 

8.7 

(0. 09)4 

30.3 

(0. 28)4 

28.4 

(0.34)4 

23.9 

(0. 27)4 

21.7 

(0.24)4 

26.7 

(0. 30)4 

The length of the cage culture interval was 105 days (consolidated cages) for group 1; 76 days (consolidated cages) for group 2; 105 

Percent of fish of target size was 72 and 78%. 

One cage had 70% of fish of target size. 

Growth rate (g/d) for the culture interval. 

days for group 3; and 79 days for group 4. 

270 NCRAC Culture Series 101- Walleye Culture Manual 
Cage Culture of Walleye - Chapter 10 

(42kg). They averaged 5.9-in (150 mm) at harvest. 

Final density was 9-11 fish/ft3 (318-385/m3). 

Discussion 

The objective of these trials was to convert pondcultured walleye fingerling in cages and then to raise 

them to a target size of 6 in (150 mm). Four groups 

were evaluated in three years, groups 1,2, and 3 were 

taken straight from ponds, but group 4 was trained to 

accept formulated feed before it was stocked. Survival 

of groups 1, 2 and 3 ranged from 6.5-23.1, whle that of 

group 4 was 85.6%. Although a simultaneous comparison of feed-trained fish (group 4) with fish taken 

directly from ponds (groups 1,2 and 3) was not done, 

the findings are a strong basis for recommending 

stocking cages with feed-trained fish. 

If the field trials were evaluated on the basis of the 

percentage of fish that reached the 6-in (150-mm) target 

size, the 1990 field trial was the most successful 

because 72 and 78% of the surviving fish in the two 

cages reached the target size. In 1991 (group 4), 70% of 

the fish in one of three cages reached the target size; 

however, fish in group 4 were raised for only 79 d while 

group 3 fish were raised for 105 d. 

Using all groups as a database, the correlation between 

stocking density and survival was low (-0.41, P > 0.05), 

as was the correlation between density and growth rate 

(-0.54, P > 0.05), but these correlations suggest that 

density has a negative effect on both survival and 

growth. The correlation between growth rate and 

survival (0.68, P e 0.05) was significant, which suggests that growth rate is affected by fish health. 

Two commercial vibrator feeders per cage worked best 

for training purposes; however, after fish were trained, a 

single feeder was adequate. Medicated feed seemed to 

help reduce disease, but stocking healthy fish in good 

condition is more important. There are no approved 

chemotherapeutics for treating bacterial dneases of 

walleye; because this was an experimental project, 

several treatments were evaluated. We tried treating fish 

that had columnaris with one-minute dip treatments in 

copper sulfate or Diquat; however, netting fish from the 

cages was labor intensive and further stressed weak 

fish. Direct application of copper sulfate or Diquat to 

the cages was ineffective because the chemicals were 

quickly &luted. Surrounding cages with clear plastic 

and giving standing bath treatments with Diquat was 

also ineffective. Generally, mortalities seemed to 

subside as an epizootic ran its course, rather than from 

any treatment efforts. The key to disease control is to 

stock healthy fish and reduce handling to a minimum. 

References 

Bushman, R. P. 1996. Cage culture of walleye and 

walleye x sauger hybrids. Pages 261-266 in R. C. 

Summerfelt, editor. Walleye culture manual. NCRAC 

Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, 

Ames. 

Kuipers, K. L., and R. C. Summerfelt. 1994. Converting 

pond-reared walleye fingerlings to formulated feeds: 

effects of diet, temperature, and stocking density. 

Journal of Applied Aquaculture 4(2):31-57. 

NCRAC Culture Series 101 - Walleye Culture Manual 271 
Chapter 10 - Cage Culture of Walleye 

272 NCRAC Culture Series 101- Walleye Culture Manual 
Stevens, C. G. 1996. Cage culture of walleye and its hybrids to food size. Pages 273-274 in R. C. 

Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North Central Regional 

Aquaculture Center Publications Office, Iowa State University, Ames. 

Cage Culture of Walleye and its Hybrids to 

Food Size 

Charles G. Stevens, 1405 West Howard, Knoxville, IA 50138 

Introduction 

This paper describes techniques I have used to raise 

walleye to food size in cages. The cages were located in 

strip mine lakes in south-central Iowa. 

Methods 

The cages I used to habituate pond-reared fingerling 

walleye to dry diets, measured 3 x 4 x 10 ft (0.91 x 1.22 

x 3.05 m) (width x depth x length), with 3/~6-in (4.8- 

mm) mesh openings. The cages were attached to a 

floating dock where water depth under the cages was 8- 

10 ft (2.44 -3.05 m) deep (2 net pens can be attached to 

each dock). Two pieces of 0.5-in (12.7-mm) plywood 4 

x 4 ft (1.22 x 1.22 m) with a 16-in (0.406-m) hole 

centered in them are placed over each net pen. The 

plywood supported the feeders and provided shade for 

the fingerlings. One 0.25-in (6.35-mm) air line with an 

airstone, 2 x 2 x 4 in (50.8 x 50.8 x 101.6 mm), was 

placed in each cage to provide supplemental aeration. 

Four vibrating feeders (2/cage) with conical extensions 

and covers were also placed on the cage dock configuration. 

Walleye fingerlings were harvested from ponds in 

southern Iowa during the second and third week of June 

when the fingerlings were 2-3 in (51-76 mm) in length 

and 600 fish/lb (I ,322/kg). Each cage was stocked with 

2,500 fingerlings. The fingerlings were fed every 3-5 

min during the initial training period. Fry Feed Kyowa 

(FFK) C2000 (Biokyowa Inc., Chesterfield, MO) was 

fed at 10% body weight/d for the first 7 d, at which time 

they were weaned to the Fish and Wildlife Service W16 formula, or a commercial salmon starter diet. At this 

time, the 9206 formula of Richard Barrows, (USFWS, 

Bozeman, Montana) would be preferred. Each day, the 

amount of FFK C2000 starter &et was reduced, and by 

16 d the surviving fingerlings were ready for 4 granules 

of W-16. By 26 d, the surviving fingerlings, which now 

readily accepted formulated feed, were moved to 

another set of cages. 

Feed-trained fingerlings were stocked at 1,000 fisldcage 

in cages that measured 4 x 8 x 8 ft (1.22 x 2.44 x 2.44 

m), with 0.25-in (6.35-mm) mesh. The cages had 

aluminum tops with a 16-in (0.406-m) hole cut into the 

center for feeding. Vibrating feeders with conical 

extensions were used to feed the fish. The fingerlings 

were fed at 3-4% body weight/d; they were fed every 30 

min in two, 3-h feeding intervals; the first began just 

before daylight, and the second began just before dusk. 

At least 10% of the fish were sampled monthly with a 

dipnet to measure growth. The daily feedmg rate was 

adjusted after sampling to the larger total biomass. 

Some mortalities usually resulted from handling stress, 

however, the monthly assessments of growth was 

necessary to calculate growth rates and to adjust 

feeding rates. 

By fall of the first year, walleye fingerlings reached 

about 8 in (203 mm), they were graded and the larger 

fish were moved to cages that had 0.5-in (12.7-mm) 

mesh openings and measured 4 x 8 x 8 ft (1.22 x 2.44 x 

2.44 m). The fish were stocked at 500 fishkage and fed 

at 3% of their body weight/d. Aeration with &ffused air 

(air stones) in the cages kept an area around the cages 

ice-free over winter. (Figure 1). 

Figure 1. Cages kept ice-free all winter with diffused air. 

NCRAC Culture Series 101 - Walleye Culture Manual 273 
Chapter 10 - Cage Culture of Walleye 

By the the second spring, some fish reached 10-12 in 

(254-305 mm); but most were 8-10 in (203-254 mm). 

When the fingerlings reached 10-12 in (254-305 mm), 

they were again graded and divided. Fish were moved 

to identically sized cages with either 0.5-in (12.7-mm) 

or 0.75-in (19.0 mm) mesh openings. They were 

stocked at 225-250 fishkage. The fish were still fed at 

3% of their body weight. 

Near the end of the second growing season, most of the 

fish were in the 12-14 in (30.5-35.5 cm) range. They 

were again dwided and graded. These fish were stocked 

in (19.0 mm) mesh opening. The fish were stocked at 

125 fiswcage. Because of the larger size, large quantities of feed are used and any mortalities during this time 

can be quite costly. Fish did not reach 1.5-2 lb (0.681- 

0.91 kg) until the middle to latter part of the third year. 

Slun-on fillet dressout was 45-50%. 

into cages 4 x 8 x 8 ft (1.22 x 2.44 x 2.44 m), with 0.75- 2. 

3. 

Suggest ions 

1. Water quality is an important part of a successfully managed cage production system. Variables 

. 

such as pH, temperature, dissolved oxygen, total 

ammonia, and alkalinity should be monitored. 

Water quality should be monitored weekly when 

growing larger fingerlings. Measurements should 

be made both inside and outside the cages. It is 

necessary to aerate the water around the cage to 

prevent ice formation in and around the cage 

system and to allow the fish to feed. In the stripmine lakes where this study was done, maximum 

depths were around 40 ft (1 2.2 m), but aeration 

was maintained with airstones to a depth of 10 ft 

(3 m). 

Cages should be cleaned monthly from April 

through October. Snorkeling or SCUBA equipment expedites the cleaning process. This type of 

equipment can also be used to visually observe 

fish in the cages. 

Walleye will continue to feed down to a water 

temperature of 40°F (4.4 "C). Winter feeding 

should be done at 0.5% body weight/d. 

274 NCRAC Culture Series 101- Walleye Culture Manual 
Blazek, K. 1996. Cage culture of walleye at Mormon Trail Lake, Iowa. Pages 275-276 in R. C. 

Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North Central Regional 

Aquaculture Center Publications Office, Iowa State University, Ames. 

Cage Culture of Walleye at Mormon Trail 

Lake, Iowa 

Kevin Blazek, Adair County Conservation Board, 705 NE Sixth, Suite A, Greenfield, Iowa 50849 

Introduction 

The objective of the cage culture project at Mormon 

Trail Lake, Iowa was to raise walleyes from about 3-3.5 

in (76-90 mm) to about 6 in (15.2 cm) for release into 

the lake, which has an existing population of largemouth bass. The lake is a 35 acre (14.2 ha) artificial 

impoundment located in southwest Iowa. Water depth 

where the cage was located was about 23 ft (7 m). 

Walleye culture was to be done on a low budget, using 

cages and feeders previously used for a channel catfish 

Mortensen (1987). An illustration and description of 

that feeder is given by Bushman (1995). Materials to 

make the feeder cost about $1 2. Feeding frequency (48 

times/d) was controlled by an electronic timer powered 

by a 6-V rechargeable gel battery. 

In 80 days, walleye were fed a total of 17 lb (7.7 kg) of 

#4 crumbles, 50 Ib (22.7 kg) of 3/16-in (4.8-mm) 

pellets, and 25 lb (1 1.4 kg) of 1/8-in (3.2-mm) pellets of 

the W-16 diet formulation (Glenco Mills, Glenco, MN). 

cage culture program, with about 15-30 min of labodd 

to feed the fish. Walleye were harvested 80 d after stochng (October 

19). The fish averaged 5.2 in (132 mm), and ranged 

from 2.9-6.7 in (74-176 mm). Survival was 84.3%. The 

253 walleyes that were harvested were stocked in the 

lake. Major problems encountered in the 1987 trial 

were dfficulty in calibrating the feeder to maintain a 

1987 Trial 

On July 31, 310, 3-in (77-mm) walleye were purchased from a private hatchery and stocked in the cage. 

The fish had been trained to eat a formulated feed (W16) for about 4 or 5 weeks prior to delivery. The fish 

were transported from the hatchery in plastic bags with Figure 1. Cage frame (4 x 4 x 8 ft), (1.2 x 1.2 x 2.4 m) 

a small volume of water and a larger volume of pure 

oxygen. Transportation loss was 3.2%, which 

was considered low considering the 100°F 

(37.8"C) air temperature when the fish 

were transported from the hatchery 

to the lake. 

After acclimation to the lake 

water, fish were stocked 

made with 1.5 in (3.8 cm) PVC pipe. 

immediately into a floating 

cage with a 1.5-in (38-mm) 

PVC pipe frame (Figure 1). 

The frame was covered with 

0.5-in (1 3-mm) plastic mesh 

but also lined with 0.25-in 

(6.0-mm) plastic mesh to 

prevent the 3-in (76-mm) 

fingerlings from escaping. The 

feeder was fabricated of PVC 

pipe from a plan developed by 

275 NCRAC Culture Series 101 - Walleye Culture Manual 
Chapter 10 - Cage Culture of Walleye 

consistent delivery rate, difficulty monitoring growth 

and condition of fish without removing them from the 

cage, and determining if the walleyes were eating. 

1988 Trial 

A new PVC pipe frame cage was fabricated, and 

covered with 0.25-in (6.35-mm) plastic mesh. The same 

feeding system was used, but the feeder was modified. 

A heavier gauge aluminum feed dispensing plate, motor 

bracket, and lower shaft alignment bracket replaced the 

30 gauge aluminum flashng plate and brackets used the 

previous year. These modifications improved the 

accuracy of the calibrated feeder rate and dependability. 

On July 15, 400, 3.5-in (88.9-mm) feed-trained walleye 

were stocked. The temperature at stocking was 75°F 

(24°C) at the surface and 73°F (23°C) at 4 ft (1.2 m). 

Over the 102-d culture period, we fed 50 lb (22.7 kg) of 

#4 crumbles, and 85 lb (38.6 kg) of 3/32-in (2.4-mm) 

pelleted W- 16 feed. Fish were fed 48 times/d. On 

October 25, we harvested 286 walleye (71.5% survival) 

that averaged 6.4 in (1 6.3 cm) and ranged from 4.5-7.9 

in (11.4-20.1 cm). 

The main problem encountered during 1988 was high 

water temperatures. The August temperature in the top 

4 ft (1.2 m) was 84°F (29°C) for 3 weeks. An epizootic 

of undetermined etiology caused mortality of 3-9 fish/ 

d. The major symptom was a white growth on the tip of 

the tail and or the base of the dorsal fin. Feeding 

terramycin treated feed seemed to be beneficial. 

1989 Trial 

In 1989, the private hatchery that provided the trained 

walleyes in 1987 and 1988 was unable to raise any fish. 

Consequently, fish were purchased from two other 

private hatcheries (designated A and B). We purchased 

405 2.25-in (57-mm) fingerlings from hatchery A. 

Transportation losses from hatchery A were 19.9%. The 

fish appeared to be in poor condtion, which, coupled 

with the 100°F (37.8"C) temperature on the day of 

transportation, may account for the hgh transportation 

losses. Later we found out these fish had been held in a 

tank in a pickup for 12-15 h prior to delivery, On 

October 25, 108 walleye were harvested from cage A. 

Survival was 26.6%. Average length was 6.1 in (15.5 

cm) and ranged from 4-7.9 in (102-201 mm). 

On July 28,485 2.5-in (63.5-mm) feed-trained walleye 

were acquired from hatchery E; they were stocked in a 

second cage (cage B). Transportation loss was 3%. On 

October 25, after 89 days in culture, 268 walleye were 

harvested (55.3%). Fish from cage B averaged 5.3 in 

(1 35 mm) and ranged 4-7.9 in (1 02-201 mm). 

In 1989, we fed a total of 50 lb (22.7 kg) of # 4 

crumbles and 100 lb (45.4 kg) of 3/32-in (2.4-mm) 

pellets of W-16 purchased from Sterling H. Nelson & 

Sons, Inc. Murray, Utah. The fish were fed 48 times/d. 

Survival from stocking to harvest in 1989 was much 

less than that in 1987 and 1988. The fish purchased 

from hatchery A were delivered in poor con&tion. The 

fish purchased from hatchery B seemed to be in good 

condition, but they had not been sorted by size. We 

think that the large range in size of fish in cage B 

resulted in cannibalism. 

A major problem encountered in this project was 

finding a steady affordable source of healthy, feedtrained fish, graded to a uniform size. Perhaps when 

tank-culture of walleye can be used to produce 3-in 

(7.6-cm) feed-trained fingerlings, the chances for 

success of cage culture will be greatly improved, and 

cage culture could be used to expand production of 

state hatcheries to meet local needs for small lake 

management. 

References 

Bushman, R. P. 1995. Cage culture of walleye and 

walleye x sauger hybrids. Pages 261-266 in R.C. 

Summerfelt, editor. Walleye culture manual. NCRAC 

Culture Series 101. North Central Regional Aquaculture Center Publications Office, Iowa State University, 

Ames, Iowa. 

Mortensen, S. 1987. Reliable and inexpensive fish 

feeder. Proceedings of annual meetings Coolwater 

Fish Culture Workshop. Albia, Iowa. 

276 NCRAC Culture Series 101- Walleye Culture Manual