Summerfelt, R. C. 1996. Intensive culture of walleye fry. Pages 161-1 85 in R. C. Summerfelt, 

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

Aquaculture Center Publications Office, lowa State University, Ames. 

Intensive Culture of 

Walleye Fry 

Robert C. Summerfelt, Department of Animal Ecologx lowa State Universit~ Ames, IA 500 1 1-322 7 

Introduction 

walleye may be raised from newly hatched fry to 

phase I fingerlings (1.25-3.0 in; 32-76 mm) in extensive 

(i.e., ponds) or in intensive culture, that is in tanks and 

raceways. Currently, the predominant method for 

raising phase I fingerlings is in drainable (Summerfelt 

et al. 1996) or undrainable ponds (Kinnunen 1996). 

Nickum and Stickney (1993) stated that “Since successful rearing of first-feeding fry under intensive culture 

conditions has not been economically accomplished, 

walleye culture has been based on pond rearing until the 

fish reach at least 2.5 rn. Thereafter, the fish may be 

offered formulated feeds.” The latter refers to the 

procedure of habituated pond-raised fingerlings to 

formulated feed in intensive culture systems (Malison 

and Held 1996). However, walleye fingerlings may be 

raised from first-feeding fry in intensive culture 

systems, hereafter called “intensive culture of fry.” This 

can be done because major constraints to intensive 

culture of fry (noninflation of the gas bladder, 

nonfeeding, and maladaptive clinging behavior) have 

been resolved, and production-scale systems for 

intensive culture have been developed. The case studies 

by Colesante (1996), Moodie and Mathias (1996), and 

Moore (1996) provide technologies for production to 

advanced fingerlings in intensive systems. Intensive 

culture is the only technology that can make use of fry 

produced by out-of-season spawning (Le., fry hatched 

in February). 

The purpose of this chapter is to provide historical 

perspective, describe critical developmental events, and 

to summarize personal experience and related literature 

on methods for intensive culture of walleye to fingerlings. 

Advantages of intensive culture 

Not many years ago, the prospects for intensive 

culture of walleye fry seemed remote because of 

seemingly insurmountable biological and technical 

difficulties. Nickurn (1978) said that “It is extremely 

speculative to suggest a culture method for walleye fry 

at this time ...” However, this chapter and the case 

studies that follow will demonstrate that critical 

problems have been solved, and many aspects of the 

culture process have been fine-tuned. It can now be 

stated that intensive fry culture is a viable production 

technology to produce walleye fingerlings. Pond culture 

is economically effective for the production of large 

numbers of phase I fingerlings, but it is far less so for 

the production of large, phase I1 fingerlings (26 in; 

21 52 mm), or for the commercial grow out from fry to 

food fish. Pond culture of phase I1 fingerlings requires 

relatively low initial pond stoclung densities, or partial 

harvest and restocking, followed by provision of 

substantial quantities of minnows (Jorgensen 1996; 

Raisanen 1996). Because of the high cost and problems 

with the availability of minnows, tandem pond-tank 

(i.e., extensive-intensive) culture methods have gained 

popularity as a method to raise fingerlings 22.5-in (264 

mm) (Cheshlre and Steele 1972; Beyerle 1975; Nagel 

1974, 1976; Nickum 1978; Colesante et al. 1986). 

The extensive-intensive method involves the transfer of 

pond-raised phase I fingerlings to intensive culture 

systems where the fish are habituated to formulated 

feed-details are described in the chapter by Malison 

and Held (1 996). In extensive-intensive culture, 

substantial mortality typically occurs at two intervalsfirst in the pond (McIntyre et al. 1987), and secondly in 

the intensive culture system during the first 21-days 

when fish are habituated to formulated feed (Kuipers 

NCRAC Culture Series 101 - Walleye Culture Manual 161 
and Summerfelt 1994). Pond culture techniques must be 

contrived to manipulate complex ecosystems within the 

constraints of variable weather: fertilizers are added 

with the expectation that food webs will provide the 

right kind and size of zooplankton for first feeding 

walleye, but without over fertilizing, causing an oxygen 

depletion, or growing aquatic weeds. When zooplankton populations are laclung, cannibalism may occur in 

the pond (McIntyre et al. 1987). Also, insect predation 

may contribute to fry mortality. 

Intensive culture may be a better alternative for hatcheries that lack the pond facilities or sites for cage culture. 

In intensive culture of walleye, a single interval of high 

mortality occurs during the critical period when fish 

switch from yolk-sac nutrition (endogenous feeding) to 

active feeding (exogenous feeding), which coincides 

with the interval of gas bladder inflation. The critical 

interval occurs before the fish reach 21-d posthatch; 

thereafter, with suitable feeds and appropriate husbandry, fingerlings may be raised to whatever target 

size is needed, or to the limits of the cultural system, 

whichever occurs first. 

Techniques for intensive culture of fry on formulated 

feed have developed sufficiently to make the intensive 

culture of fry to fingerling a practical alternative to the 

extensive-intensive system. Will intensive culture of fry 

replace pond culture of fingerlings? Intensive culture 

has many factors in its favor: It is not subjected to 

variable environmental con&tions, so cultural conditions are fairly stable, temperature can be controlled to 

lengthen the growing season, nuisance aquatic organisms are eliminated, and the quality and quantity of the 

feed is controlled. Technological advances are more 

likely applicable in an the intensive culture system than 

in pond culture. In spite of hgh stoclung density, 

cannibalism may be less of a problem in intensive 

culture than pond culture because in intensive culture 

cannibalism is easier to monitor, and the environment 

(temperature, light, turbidity) or feeding rates can be 

adjusted to reduce the intensity of the problem. In 

intensive culture, growth rates can be stepped up or 

slowed by temperature manipulation to meet production 

schedules for fish of different size. 

Intensive culture is the only technology that can be used 

to raise fry produced by out-of-season spawning. The 

advantage of out-of-season culture is that it increases 

the growing season. Ambient water temperature during 

the natural culture season is usually too short to raise a 

phase I1 fingerling to a target size of 6 to 8 in (152-203 

mm) by fall in either ponds or cages. In 1995 and 1996, 

Moore (Alan Moore, Iowa Department of Natural 

Resources, personal communication) spawned walleye 

in late January at the Rathbun Fish Hatchery. A sample 

of eggs from those spawns hatched in mid February. 

Fry produced by out-of-season can be raised in intensive culture, but they could not be stocked in ponds 

anywhere in the Midwest. In Iowa, pond stocking is not 

feasible until mid-April in the southeastern corner of 

the state, and the first week in May in the northwest 

comer (Jorgensen 1996). Pond stoclung begins in midto late April in Ohio, mid-April in western Nebraska 

(Summerfelt et al. 1993), late April-early May in lower 

Michigan (Gustafson 1996), early May-early June in 

North Dakota (Summerfelt et al. 1993), the third week 

of May in northern Michigan (Wright 1996), and late 

May-early June in May in Ontario (Flowers 1996). 

Would intensive fry culture with heated water be 

economical for commercial producers? As a rule, 

heating water for production aquaculture is uneconomical, but several small and a few large commercial 

aquaculture facilities in the Midwest, includmg sites in 

Minnesota and North Dakota, raise tilapia indoors; they 

heat and recycle water at temperatures 84-88°F (28.9- 

3 1.1 "C). The larger operators typically have a source of 

steam or warm water from coal-fueled electric generating plants or facilities that distill alcohol. Recycle 

systems have been used for intensive culture of walleye 

fry at sites as far north as near Gunton, Manitoba 

(Loadman et al. 1989; Moodie et al. 1992). Walleye can 

be raised from hatch to a subadult in one calendar year 

in an intensive system with optimum water temperature. 

Fingerlings started from out-of-season spawning and 

raised in intensive culture may find a special niche for 

commercial production of feed-trained fingerlings for 

cage culture and other intensive culture systems. 

Fingerlings from early spawned fish can be available in 

advance of young-of-the-year fingerlings produced 

from ponds or from extensive-intensive culture. 

Because of the dfficulty in habituating pond-raised 

fingerlings to formulated feed, a commercial source of 

feed-trained fingerlings is critical for the successful 

cage culture of walleye to a fall (advanced) fingerling. 

Disease and cannibalism are less and survival is greater 

in cages stocked with feed-trained walleye fingerlings 

than in cages where pond-raised fingerlings are 

162 NCRAC Culture Series 101- Walleye Culture Manual 
habituated to feed (Blazek 1996; Bushman 1996; 

Harder and Summerfelt 1996). 

Historical perspective 

Public hatcheries have spawned, incubated, and 

hatched walleye for more than 100 years. The Manual 

of Fish-Culture published by the U.S. Commission of 

Fish and Fisheries in 1900 has a chapter on “The Pike 

Perch or Wall-Eyed Pike” (USCFF 1900). That chapter 

describes spawning and spawn-taking, use of “swamp 

muck” to prevent adhesion of eggs, egg-incubation, 

transportation of eggs, description of cannibalism 

(includmg some excellent photographs of cannibalism), 

and prey selectivity by first feeding fry when lake water 

containing zooplankton was used for the water supply. 

There was no mention, however, of pond culture of 

fingerlings or any attempts at intensive culture of 

walleye. 

Since 1900, techniques for spawning, incubation and 

hatching of fry improved and substantially expanded. A 

survey conducted by Tunison et al. (1949) in 1948, with 

data for hatcheries of 44 States and the U.S. Fish and 

Wildlife Service, listed the distribution of 596.4 million 

“wall-eyed” pike, and 79.6 million yellow pike-perch 

fry, and 485.4 million “unclassified” pike-perch. If we 

presume that all of these categories are walleye, the 

total was 1.16 billion fry. That level of production 

seems to have persisted for forty years. A survey in 

1983-84, indicated a similar number of fry were 

stocked annually by state, federal and provincial 

agencies in the U.S. and Canada (Conover 1986). 

The first mention of pond culture of fingerlings dates 

from the early 1920’s (Cobb 1923). Thereafter, accounts of dstribution of walleye fingerlings were 

reported. In 1948, using the same categories noted 

above, fingerling distribution was more than 4 million 

(Tunison et al. 1949). By 1983/84, more than 9 million 

pond cultured fingerlings were stocked (Conover 1986). 

The beginnings of intensive culture is somewhat 

obscure. But because many public hatcheries had tanks 

and raceways available at the time walleye fry were 

hatching, and plenty of fry available for experimentation, the commencement of intensive culture was 

inevitable. Hatchery biologists carried out many trialand-error experiments to culture walleye fry. Olson 

(1974) reported stocking 20,000 walleye fry in a 750 

gallon (2839 L) tank (7 fry&) and providmg them with 

zooplankton from the water supply taken from a nearly 

lakes. The fry refused to eat the zooplankton, and 

cannibalism was severe; less than 100 fry survived to 12 

days. 

Some early studes were reported at the annual meetings of the Coolwater (Fish) Culture Workshop. Begun 

as a small group of hatchery biologists that gathered to 

discuss cultural problems of muskellunge and tiger 

muslue, in recent years, more presentations have been 

made on walleye than any other species. Certainly, the 

development of the cultural technology for walleye 

owes much to exchange of information that occurs at 

the annual workshop meetings. Unfortunately, due to 

the informality of the meetings, proceedings or minutes 

of the meetings have been limited to the registrants, and 

no repository for the minutes exists. 

Cheshire and Steele (1 972) stated that no literature 

could be found on the culture of walleye fry using 

artificial food. But they were among the earliest 

investigators to train 2-in (50-mm), pond-cultured 

fingerlings to accept formulated feed. Beyerle (1975) 

cited four unpublished reports by personnel at state and 

federal hatcheries on intensive culture of walleye fry 

using formulated feed, but those attempts were “uniformly unsuccessful”, no fry survived beyond 17 days 

after yolk sac absorption (i.e., about 22-25 days 

posthatch), and no dry &et was accepted by walleye fry. 

In 1974, the inadequacy of hatchery technology for the 

culture of larval walleye on artificial diets was noted by 

the National Task Force for Public Fish Hatchery Policy 

(FWS 1974) as “the most critical bottleneck in the 

national fish-culture program.” 

The earliest success with intensive fry culture was 

obtained by feeding live food. Beyerle (1 975) raised 

walleye fry in fiberglass troughs to 32 days with 3.9% 

survival by feeding them a combination of brine shrimp 

and daphnians. Thus, aside from what may have been 

done by others but not published, or that which was 

described in the so-called “gray literature” (unpublished 

reports and workshop proceedings that are difficult to 

obtain), Beyerle’s (1975) report may be marked as the 

start for intensive culture of walleye fry using live feed. 

In summarizing the state of the art on feeding formulated feed, Nickum (1978) stated that although fry often 

ingested formulated feed, survival to 21 days posthatch 

NCRAC Culture Series 101 - Walleye Culture Manual 163 
was less than 1%. Also, few fry survived weaning to 

formulated dets when they were started feeding on 

brine shrimp and zooplankton (Nickum 1978). 

Krise and Meade (1 986) reviewed unpublished and 

published reports on intensive culture of walleye fry 

through 1983. The early 1980’s was a period of intense 

activity; the topics included: developmental biology of 

the fry; the visual system of walleye, especially how 

color contrasts of food and tank affect feeding success; 

phototaxis of larvae (photopositive until they reach 31 

mm); and effects of light intensity, water flow, temperature, stochng density, feeds and feeding techniques. 

“Ineffective feeding” was considered the major problem, but cannibalism during the first two weeks was 

also considered to be a significant problem. For the 

most part, formulated diets were not successful as 

starter feed. Fish that ate the feed ded within a few 

weeks for unknown reasons. 

Howey et al. (1 980) obtained a remarkable 43.5% 

survival through three weeks “post-swimup” by starting 

walleye fry on live food (brine shrimp, followed by 

daphnia), then weaning them to a formulated feed. They 

stocked fry at 14 fry& and fed them brine shrimp 

nauplii at 30-rnin intervals over an 18-h photoperiod at 

a water temperature at 64.4-68°F (18-20°C). They fed 

daphnia for an additional 3-4 weeks, then gradually 

converted the fish to the U.S. Fish and Wildlife Service 

W-7 diet formulation. They reported about 20% of the 

surviving fish had failed to inflate their gas bladder, 

which seem to be the first report on the problem of noninflation of the gas bladder (NGB). Howey et al. (1980) 

stated that NGB “may be embryological or related to 

low level (1 00-1 03 %) nitrogen gas supersaturation in 

the water supply.’’ Although their conjecture was wrong, 

their dscovery of the NGB problem was subsequently 

regarded by many as the major problem in the intensive 

culture of walleye fry (Colesante et al. 1986; Barrows et 

al. 1988; Kindschi and MacConnell 1989; Loadman et 

al. 1989). Kindschi and MacConnell(l989) reported 

gas bladder inflation from 0 to 50%, and mostly less 

than 30% in 20 trials using five formulated feeds and 

combinations of formulated feeds with brine shrimp. 

Some efforts to develop commercial scale fry culture 

systems are still plagued by problems with NGB 

(Moodie et al. 1992). 

Hokensen and Lien (1986) obtained 71% survival of 

walleye fry to 21 days in 20 L aquaria feeding zooplankton captured from a pond, but fry survival in 

experiments with formulated feed was usually 40% 

(Colesante et al. 1986; Barrows et al. 1988; Kindschi 

and MacConnell 1989). However, the availability of a 

commercial fry feed, the Fry Feed Kyowa (FFK) 

(Eiokyowa Inc., Chesterfield, Missouri) E-series feed 

was an important advancement. The B-series, designed 

as a replacement for artemia, became the standard 

starter feed used by most investigators (Loadman et al. 

1989; Moore et al. 1994a,1994b; Bristow and Summerfelt 1994; Bristow et al. 1995; Moodie and Mathias 

1996; Moore 1996). The B-series is available in 

nominal sizes categories: E-400 (400 pn), E-700 (700 

pn), etc. Most investigators start fry on the FFK B-400, 

then upgrade to the E-700, and so forth, as the fish 

grow. Because of a large price difference between the €3 

and C series, most culturists now start fry on the E-400, 

then switch to the C-700. Barrows (1996) describes a 

less expensive, open formula starter &et for walleye 

(WS-9501) developed at the U.S. Fish and Wildlife 

Service Fish Technology Center, Bozeman, Montana. 

The experiments with the FFK formulated feed gave 

promising survival rates, but NGB continued to be a 

problem. For example, Loadman et al.( 1989) reported 

survival of 27.7% to 30 d for walleye raised at 669°F 

(1 9.4”C) and fed exclusively with formulated feed, but 

gas bladder inflation was about 16%. Viability, the 

product of survival and gas bladder inflation is a 

measure of potential for longterm survival. In the study 

by Loadman et a1.(1989), viability was only 4.4% 

([0.277 x 0.161 x 100). Loadman et al. (1989) reported 

that of the survivors to 132 d posthatch, 40% had 

inflated gas bladders. Because fish cannot inflate their 

gas bladder much later than 12-d posthatch (Marty et al. 

1995), my calculations suggested that 52% of the fish 

with the NGB problem died between 30 and 132 days. 

The development of intensive culture technology has 

been accomplished through a succession of successful 

problem solving of critical bottlenecks. For example, a 

water spray has been used to overcome the NGB 

problem (Barrows et al. 1993b; Moore et al. 1994a). A 

portion of the inflow is passed through a 90” perimeter 

nozzle directed perpendicular to the water surface. The 

impact of the spray seems to clean the surface of oil and 

other debris from the tank surface, but whatever the 

physical mechanism, it works. Since tanks have been 

equipped with a surface spray gas bladder inflation 

rates of 90 to 100% have been common (Barrows et al. 

164 NCRAC Culture Series 101- Walleye Culture Manual 
1993b; Moore et al. 1994b; Bristow and Summerfelt 

1994; Bristow et al. 1996). Gas bladder inflation is 

discussed in the section on Noninflation of the Gas 

Bladder. 

Another critical bottleneck is the tendency for fry to 

cling to the culture tank. Some investigators suggested 

that the clinging behavior was the result of stress 

syndrome behavior, or from NGB. Fish with the stress 

syndrome behavior (Beyerle 1975) swim in a circular 

motion or move to the sides of the tank and face the 

tank wall (Krise and Meade 1986). Clinging behavior 

may be an attraction of the fry to reflected light. 

Walleye fry are strongly attracted to strong overhead 

light, but they also cling to the tank walls, standpipe or 

any other shiny surface that reflects light. Two techniques have been used to disperse the fry and prevent 

clinging: Bristow and Summerfelt (1994; Bristow et al. 

1996) use turbid water and Colesante (1996) uses hgh 

intensity light. Further lscussion of the problem of 

clinging behavior is given in the section on Clinging 

Behavior. 

Developmental biology of walleye 

To this point, what has been referred to as a fry is 

really a vernacular name used by fish culturists to 

encompasses several discrete developmental stages 

from hatching to juvenile, that is from fry to fingerlings. 

Development does not proceed by gradual changes, but 

by major steps, a process called saltatorial development 

(Balon 1975). The technical terminology used to 

describe the developmental stages of larval fishes is 

diverse, only those few that concern walleye will be 

referenced here. Hubbs (1 943) used prolarva for the 

stage with the yolk sac, postlarva for the stage after 

hsappearance of the yolk. Balon (1975) called the yolk 

sac stage an embryo and the larva stage as the interval 

from first feeding to the juvenile. Nelson (1968) used 

similar terminology to that of Hubbs but defined the 

change from prolarva to postlarva by disappearance of 

the oil globule, an event that takes about 5 days 

additional days after disappearance of the yolk. Li and 

Mathias (1982) used prolarva for fish with a yolk sac, 

and divided the postlarva into a postlarva I and 11. Krise 

and Meade (1 986) used stages and temperature units 

(TUs, cumulative daily temperature in "C): Stage 1, 

surface suspension (7-29 TU); Stage 11, initiation of gill 

respiration (70 TU); Stage 111, initiation of feeding 

(120-t TU); and Stage IV, initiation of cannibalism and 

gas bladder inflation (1 00-2 14 TU). 

The terminology of Li and Mathias (1982) is that most 

commonly used by most US and Canadian researchers. 

Their report suggests that at 64.4 to 68°F (18-20°C), the 

prolarva lasts 5-6 days, postlarva I and postlarva I1 

about 5 days each for a total of 15-16 days from hatch 

to juvenile. In my laboratory, where culture temperatures do not reach 20°C until about 30 days posthatch, 

the postlarval I1 stage does not end until 16- to 19-d 

pos thatch. 

Prolarval stage 

The prolarval stage is also called a free embryo or 

eleutheroembryo (Balon 1984), or finfold stage. Fish 

culturists call them sac fry because it is the first period 

of life post-hatch when the yolk sac is present (Figure 

1). No paired fins are present and the mehan fin (fin 

fold) is transparent, and continuous from the head 

around the tail to the anus. Yolk sac length measured by 

Bristow and Summerfelt (in preparation) was 1.34k0.16 

mm (coefficient of variability, CV, was 11.9%), or 

18.1% of total length; the oil globule dameter was 

0.86k0.14 mm (CV was 16.3%) at hatching, or 11.9% 

of total length at hatch. Li and Mathas (1982) reported 

that oil globule diameter was 0.4-0.6 mm for prolarva, 

but this seems more appropriate for larvae at the end of 

the prolarval phase. Olson (1974) reported an oil 

globule lameter of 0.9 mm at hatch for 1 day old, 7.1 

mm, long fry. 

At a mean temperature of 16.4"C, the yolk sac disappears in the 5th day posthatch, about 68 TU (Bristow 

and Summerfelt, in preparation), but it may persist up to 

about 13 days at a temperature of 13.2"C (calculated 

from data given by Hurley 1972). Olson (1974) 

reported that the yolk sac &sappeared in 10-1 1 days 

(temperature not given). Larval nourishment at this time 

is said to be endogenous because it precedes (exogenous) feeding, in fact, the mouth is closed until 3- to 4- 

d posthatch. 

The prolarvae are weak swimmers, so water currents in 

culture tanks should be low, because larvae are quickly 

exhausted. Their weak swimming ability also causes 

problems in shipping larvae in plastic bags. Prolarvae 

often are shipped in plastic bags at 100,000- 150,000 per 

15 L of water, and transported for up to 18 hours, but 

unless the bag is moved to and fro by the motion of the 

NCRAC Culture Series 101 - Walleye Culture Manual 165 
Gas bladder develops here / 

1 ’ qksaclength I 

-. Oil globule diameter I 

f*- Total length -* 

Figure 1. Photograph of the finfold, or prolarval stage of walleye taken 10- 

minutes after hatch. Dimensions used for measurement of yolk sac and oil 

globule are shown. 

vehicle, the larvae pile up and suffocate (Colesante and 

Schiavone 1980). 

stage is 8-9 mm. In the spring 

of 1992, measurements were 

made of the total length of 150 

fry from each of six stocks of 

walleye from the Midwest that 

were collected one-hour after 

hatch: the mean (LSD) total 

length for 900 newly hatched 

fry was 7.4k0.55 mm (CV was 

7.4%), individual stock means 

varied from 6.9 to 8.2 mm 

(Hey et al. 1996). Oseid and 

Smith (197 1) found that mean 

length of walleye at hatch 

varied in relation to lot (“five 

separate lots from three 

stripping stations”), which 

implies dfferences between 

stocks, parents, or both. It is 

not clear whether stock 

differences in length at hatching are heritable or a 

function of variation in nutritional condition of the 

female before spawning. Oseid and Smith (1971) also 

found that oxygen concentration during incubation and 

length of the incubation interval affected length at 

hatching: the longer the incubation interval and the 

Length at hatching ranges from 4.8 to 9.0 mm (Table l), 

but fry lengths of 9 mm probably represents measurements sometime after hatching. Li and Mathias (1 982) 

report that the length of fry at the end of the prolarval 

Table 1. Dimensions of newly hatched walleye frya. 

Length Weight Volume 

mm Ref e re nce No./g Reference No./mL Reference 

4.8 USCFF (1 900) 

6-9 Scott and 

6-8.6 Craig (1987) 

Crossman (1 973) 

7.42b Bristow (1 993) 

7.1 Olson (1974) 

5.7-7.8 Oseid and Smith 

(1971) 

207-276 Summetfelt et al. 

357 Howey et al. 

161 .3c Kindschi and 

(unpublished) 

(1 980) 

Barrows 1991 a 

1 11 -1 43 

167 Loadman et al. 

160-21 0 Colesante (1 996) 

Summetfelt et al. 

(unpublished) 

(1 989) 

220 Call (1996) 

aNewly hatched fry are called embryos by Balon (1975), or prolarvae by Li and Mathias (1982). 

bMean of 900 measurements taken within 30-minutes of hatch, 150 larvae were measured of each of six geographic 

stocks (OH, KS, IA, WI, MN, and ND) that hatched April 7 to May 29, 1992. Stock means ranged from 6.7-8.2 mm; 

there was a significant difference among all but two stocks. 

C3-day old fry. 

166 NCRAC Culture Series 101- Walleye Culture Manual 
higher the oxygen concentration, the longer the fish at 

hatching. In my laboratory, the mean lengths of two 

groups of walleye hatched from fish spawned out-ofseason were smaller than newly hatched walleye from 

the same stock that are spawned in the normal season 

(unpublished data). 

Hatchery personnel frequently measure the volume of a 

known number of 2- to 3-day-old fry as a basis for 

estimating number of fry for stocking. Information on 

number of fry/ml has not been published. In the course 

of our research, many volumetric measurements of fry 

for stocking experimental tanks have been made but the 

values are variable (Table 1). Variability may be related 

to the diversity of stocks that were used, the care or lack 

of it in removing excess water, but especially the age of 

the fish at the time of stocking. Although the fish have 

not begun to feed, the number/mL decreases with age 

from 1-4 days; measurements in our laboratory are 

usually made at the time of stoclung, about 2-3 d 

posthatch. 

Postlarva I 

Postlarva I is the stage following absorption of the yolk 

sac but before disappearance of the oil globule. After 

hsappearance of the yolk, or slightly before then, 

larvae begin feeding (exogenous feeding), and gas 

bladder inflation begins. Krise and Meade (1 986) 

indicated that first feeding begins at 100-122 TU. Our 

measurements (Bristow and Summerfelt, in preparation) indicate that the TU to yolk sac dwappearance (68 

TU) is much earlier than first feeding (132 TU). Before 

feeding, the energy requirements of the larvae for 

swimming and searching for food must be provided by 

the oil globule. First feeding walleye (8.5-9.0 mm) have 

a mouth width of 0.7 mm and a gape of 1.5 mm (Li and 

Mathias 1982), which is sufficiently large to cannibalize 

similar-sized siblings or to consume the standard size 

(400 pm) of the starter feed. 

Balon (1984) considered the transition of the embryo 

(prolarva) to exogenous feeding to be the decisive event 

in development, because failure to accomplish first 

feedmg results in mortality. Because persistence of the 

oil globule aides buoyancy and it serves the basic 

energy needs of the larvae, the peak period for mortality 

does not occur until the 16 to 19 days posthatch or at 

the end of postlarval I1 (Figure 2). 

?? 150 

Eees hatched at ISU 

0 

A- I \ 

i' I 1' 

n I I \ 

0 

0 2 4 6 8 10 12 14 16 18 20 22 24 2628 30 

Days Posthatch 

Fry shipped to ISU ,-. 1600 

0 cc 2 

-1 

0 

1 1400 -'I 

"0 1200 - !\; 

-d 

0 rn -\ 5 1000 9 0 

h 

W 800- \ 

.* 

cd 600 - 

G 8 400 - L IA h I \ 

0 2 4 6 8 10 12 14 16 18202224 262830 

Days Posthatch 

Figure 2. Mortality curve for walleye fry hatched at 

the culture site (upper) compared with curve for 

walleye hatched elsewhere and transported to the 

culture site in plastic bag (lower). It is typical to 

observe high mortality in the first few days after 

stocking of fry that were transported to the culture 

site, but not for fry hatched on site. 

Postlarva I1 

Postlarva I1 begins about the time the oil globule 

disappears ( Li and Mathias 1982), whch is about 226 

TU, in the 14th day posthatch at a mean temperature of 

61.5"F (16.4"C) (Bristow and Summerfelt, in preparation). Li and Mathias (1 982) stated that the postlarval 

stage lasted about 8 days, that is from 5- to 6-d posthatch to about 13- 14 d posthatch at 20°C. They reported 

that fish were 16-19 mm long at the end of this stage. 

Nelson (1968) marked completion of the postlarval 

NCRAC Culture Series 101 - Walleye Culture Manual 167 
stage when the adult complement of pyloric caecae (3) 

were developed. 

After the yolk sac and oil globule disappear, nutrient 

reserves are exhausted and exogenous feeding must be 

effective or the larvae quickly starve. Starving fish 

exhbit a stress syndrome behavior (Beyerle 1975), or 

they revert to prolarval behavior, swimming to the 

surface and drifting back to the bottom (Krise and 

Meade 1986). These behavioral patterns may be related 

to noninflation of the gas bladder which is discussed in 

the section titled “Noninflation of the gas bladder.” 

The end of the postlarval I1 stage marks the end of gas 

bladder inflation. Reports that show progressive 

increases in gas bladder inflation rates after this period 

are the result of mortality of fish that have not inflated 

the gas bladder, not because fish are continuing to 

inflate the gas bladder. After the first loop of the 

intestine develops the pyloric sphincter develops and 

separates the common bile duct in the intestine from the 

pneumatic duct in the dorsal wall of the stomach (Marty 

et al. 1995). This developmental event prevents walleye 

older than 12 days from inflating their gas bladder 

because air bubbles may enter the pneumatic duct only 

after the large ingested bubbles can be actively cleaved 

in the foregut. That process requires secretions with 

surfactant properties to decrease surface tension of the 

ingested bubble. The bile is a likely source of these 

secretions (Marty et al. 1995). The end of postlarval I1 

stage and beginning of the juvenile (fingerling) stage is 

not marked by conspicuous and convenient developmental milestones. The swim bladder has inflated and 

feeding successful or the fish die. Other than mortality 

related to transportation stress, the period of greatest 

mortality is 16-19 days posthatch, that is the beginning 

of the juvenile stage (Figure 2). 

Juvenile 

Juvenile stage begins about 15- 18 days posthatch at a 

length of about 20 mm. At the end of the postlarval I1 

stage, fin rays are limited to the lower lobe of the caudal 

fin, but as the juvenile stage progresses the fin rays 

develop in the rest of the caudal and other paired fins, 

and spinous rays develop. Further maturation of the 

gastrointestinal tract takes place, gill rakers differentiate, and pigmentation increases (Li and Mathias 1982). 

Scale development begins at 24 mm but it is not 

completed until they are 45 mm (Priegel 1964). 

Bulkowski and Meade (1983) described a behavioral 

change in juvenile walleye from positive phototaxis to 

negative phototaxis behavior when they are 32 to 40 

mm. In intensive culture, this change begins in juveniles 

as early as 25 mm. The changing response of juveniles 

to light is important in both extensive and intensive 

culture. In intensive culture, relatively high light 

intensity (680 lux) is used by (Colesante 1996) until gas 

bladder inflation is first detected (8-1 0 d posthatch) as a 

means to attract fry to the surface for gas bladder 

inflation. After gas bladder inflation began, he reduces 

light intensity to 140 lux for the duration of the culture 

interval to dsperse the fry vertically in the water 

column. Before they change from positive to negative 

phototaxis, fish in ponds can be attracted to light for 

night harvest (Summerfelt 1996). The change in 

behavior is also important in habituating pond-raised 

fingerlings to formulated feed, because after 40 mm 

walleye fingerlings are cultured at low (<16 lx) light 

intensity (Kuipers and Summerfelt 1994) or intank 

lighting is used (Siegwarth and Summerfelt 1992) to 

reduce stress and enhance feeding and growth. 

Critically important cultural problems 

The most critical problems affecting success of 

walleye culture are: 

1, Noninflation of the Gas Bladder (NGB) 

2. Clinging behavior 

3. Nonfeedmg 

4. Cannibalism 

These constraints had to be overcome before intensive 

culture became possible, but it seems from present 

perspective, that NGB and clinging behavior have had a 

greater impact on nonfeedmg than the suitability of fry 

feeds, and both problems influence incidence of 

cannibalism. 

Noninflation of the gas bladder (NGB) 

NGB is important because it contributes to mass 

mortality, larval deformities (lordosis) (Figure 3), 

susceptibility to stress-induced mortality, dseases and 

toxicant, it slows growth, and increases susceptibility to 

cannibalism or predation (Chatain 1986; Kitajima et al. 

1994). Fry without an inflated gas bladder struggle to 

maintain position and they eventually starve because of 

the hgh energy cost of swimming and difficulty in 

capturing food. NGB makes fry vulnerable to cannibalism because fry without an inflated gas bladder have 

168 NCRAC Culture Series 101- Walleye Culture Manual 
Figure 3. Lordotic deformity of postlarval I walleye associated with 

noninflation of the gas bladder. 

erratic behavior and poor swimming ability (McElman 

and Balon 1979). NGB in striped bass leads to decreased growth rates and increased susceptibility to 

stress (Lewis et al. 1981). Walleye fry lacking an 

inflated gas bladder are typically smaller than siblings 

which have inflated their gas bladders (Kindschi and 

McConnell 1989). NGB is not limited to walleye, it has 

been a major problem in the intensive culture of striped 

bass (Bulak and Heidinger 1980; Cornacchia 198 1 ; 

Bennett et al. 1987; Chapman et al. 1988) and other 

species (Weppe and Bonami 198 1 ; Chatain 1986; 

Chatain and Ounais-Guschemann 1990; Kitajima et al. 

1994; ). 

It was essential to develop effective 

strategies to overcome this 

imposing problem. When the 

problem was first recognized, 

many hypothesis were proposed as 

to its etiology, includmg nutrition, 

genetics and several environmental 

factors (Howey et al. 1980; 

Barrows et al. 1988; Kindschi and 

MacConnell 1989; Loadman et al. 

1989; Bushman 1992). 

In most fish, initial filling of the 

gas bladder is accomplished by 

gulping and swallowing air (Figure 

4), then mechanically forcing air 

bubbles from the foregut through 

the lumen of the pneumatic duct to 

the gas bladder (Vogt 1842, cited by 

McEwen 1940; von Ledebur 1928; Tait 

1960; Marty et al. 1995; Rieger 1995). 

Salmonids, catfishes, minnows, and other 

soft-rayed (physostomous) fishes have a 

permanent connection (pneumatic duct) 

between the foregut and the gas bladder, 

and gas bladder inflation may occur over 

an extended interval. Salmonids may fill 

their gas bladder at least three months 

after hatching (Tait 1960). On the other 

hand, most spiny-rayed (physoclistous) 

freshwater and marine fishes have a 

functional pneumatic duct for only a 

brief interval; thus, their ability to fill the 

gas bladder is limited to a short interval 

after yolk sac absorption. A few species 

of physoclistous fish do not possess a 

pneumatic duct in early larval stages-they seem to fill 

their gas bladder by secretion of gas (CO, or 02) into the 

lumen of the gas bladder from the gas gland epithelium 

(McEwen 1940; Doroshov et al. 1981). 

For walleye, the interval of gas bladder inflation after 

hatch is said to be 214 TU (that is 10.7-12.5 days at 20- 

17OC, respectively) (McElman and Balon 1979), 5-1 1 

days (Barrows et al. 1988), 7-14 days (Kindschi and 

Barrows 1993), and 6 to 12 days (Marty et al. 1995). 

Although these dates differ slightly, it is certain that the 

window of opportunity for initial gas bladder inflation 

is relatively short. It is assumed that failure of the gas 

Figure 4. Larval walleye penetrating water surface to gulp air for first 

filling the gas bladder.Third fish on right is ingesting an air bubble. 

NCRAC Culture Series 101 - Walleye Culture Manual 169 
bladder to inflate during this specific period of development is irreversible. In many teleosts, gas bladder 

inflation typically takes place shortly after the transition 

of the prolarva from yolk sac respiration to gill respiration (McElman and Balon 1979), concurrent with yolk 

sac absorption (Tait 1960), and the initiation of exogenous feeding (Battaglene and Talbot 1990). 

It has been conjecture to state that the interval for gas 

bladder inflation ended with atrophy of the pneumatic 

duct, in fact the pneumatic duct is still present when gas 

bladder inflation ceases (Marty et al. 1995). The 

inflation process is a two step procedure: The first step 

is to initiate inflation; the second is to fully extend the 

gas bladder. In the first step, air gulped at the water 

surface (Figure 4) is ingested, but bubbles must be 

small enough for passage through the 25- to 45-pn 

dameter pneumatic duct. The relatively large bubbles 

ingested at the surface are fragmented by surfactant-like 

secretions in the foregut. Marty et al. (1995) suggest 

that the surfactant is derived from the bile, which is 

discharged into the same part of the undifferentiated 

foregut as the opening from the gut to the pneumatic 

duct. The bubbles are forced by mechanical pressure 

from flexing of the gut through the pneumatic duct into 

the gas bladder (Rieger 1995). At the end of the primary 

inflation stage, the gas bladder has a spherical shape 

(Figure 5). Immediately following initiation of gas 

bladder inflation, the second stage begins when the 

vascular rete of the gas gland (located on the ventral 

surface of the gas bladder) functions to continue the 

inflation process, stepping up pressure within the gas 

bladder until the gas bladder assumes an elongatedshape (Figure 6). 

An oily layer on the water surface will prevent the 

larvae from breaking the water surface, and the primary 

stage of gas bladder inflation will not occur. Thus, NGB 

is most often the result of contamination of the water 

surface by oil. This may be from compressors or 

submersible pumps, feed or even the fry (Boggs and 

Summerfelt 1996). Interference with the second stage 

of inflation, which takes place 12 to 19 days posthatch, 

results from bacterial aerocystitis, an inflammation of 

the gas bladder epithelium. With or without oil, the 

surface tension is usually sufficient to support small 

particles of feed as well as bacteria and fungi. If the fry 

ingest surface film or partially decomposed feed that is 

heavily contaminated with microbes, feed and microbes 

may be aspirated into the gas bladder on the microfilm 

surroundmg the air bubble (Figure 7). Although gas 

bladder inflation advances to the spherical stage, 

%- 

Figure 5. Early gas bladder inflation (gas bladder is spherical) of 9- 

d-old, postlarval II stage walleye (1 6.8OC average, 151 TUs) with 

remnant oil globule. 

Figure 6. A 14-d posthatch (1 7.2"C average, 240 TUs) walleye (no oil 

globule) with elongated gas bladder and food in gut. 

inflammation of the epithelial lining of the 

gas bladder will lead to dysfunction of the 

gas gland, which prevents full extension and 

can cause deflation of the small, gas bladder. 

However, in an intensive culture environment, where formulated food is abundant, 

some fish without inflated gas bladders may 

survive. In our laboratory, some walleye 

have been raised without an inflated gas 

bladder to more than 200 mm. 

In the past, some investigators regarded 

NGB an artifact of intensive culture, but 

Kindschi and Barrows (1 993) established the 

fact NGB occurs in pond-raised walleye as 

well. They found NGB in fish from 53.7% 

of 188 ponds sampled from 15 pond culture 

facilities in nine states. Although, only 3.5% 

of 4,229 fish examined did not have an 

inflated gas bladder, the incidence of NGB 

was 55% in one pond. In another study, 

Barrows et al. (1993a) noted finding an 

incidence of 74% of 13,000 pond-raised 

fingerlings; they did not state whether that 

170 NCRAC Culture Series 101- Walleye Culture Manual 
Figure 7. Larval walleye gulping air at the water surface that is contaminated with microbes and feed particles may cause bacterial aerocystitis, 

an inflammation of the gas bladder epithelium that causes collapse of a 

partially inflated gas bladder. 

was from one or many ponds. The reports by Kindschi 

and Barrows (1993) and Barrows et al. (1993a) demonstrate that NGB is not unique to walleye reared in tanks. 

Kindschi and Barrows (1 993) also found that a small, 

but unrecorded percentage of walleyes with uninflated 

gas bladder had lordotic deformities, a condition I have 

seen in intensively raised walleye (Figure 3). Lordotic 

changes caused by vitamin C deficiency are most often 

located below the soft-rayed dorsal fin (Kindschi and 

Barrows 1993), whereas lordotic changes in the 

vertebral column from NGB are located below the 

spiny-rayed dorsal fin. Vitamin C deficiency produces 

other clinical signs of pathological changes, especially 

breakmg of the isthmus, but we have not observed 

isthmus breakage or other signs of vitamin C deficiency 

in fish with NGB. 

The effectiveness of the culture system to produce high 

percentage of fish with inflated gas bladders should be 

determined for a new system, but also routinely for 

quality control. Fish laclung an inflated gas bladder 

should not be stocked, and pond-raised fish that are 

habituated to formulated feed in the extensive-intensive 

culture procedure or stocked in cages should be 

checked for gas bladder inflation. In my research on 

intensive culture of walleye, gas bladder inflation is 

examined in fish samples from all culture tanks at 

weekly intervals from 7 to 28 days. 

At least 30 days, and 1.1 in (28 mm), 

walleye are quite transparent and the 

gas bladder easy to observe (Figure 

13). Fry are observed in a petri dish 

on a dmecting microscope, using 

transmitted light with 6-7 x magnification. Barrows et al. (1993a) 

compared four methods (light Table, 

anesthesia, saltwater floatation, and 

X-rays) for detecting the presence of 

an inflated gas bladder in fingerings 

3.1-6.6 in (80-167 mm). They 

recommended the light Table method 

or the anesthesia method (used with 

a 3% salt solution) for routine 

screening. 

Clinging behavior 

In intensive culture of walleye in 

relatively clear water (i.e., low 

turbidity), a large portion of fry cling 

to the walls of the tank. This seems to be an innate 

phototactic behavior. They swim toward light, not only 

direct light, but reflected light, even in tanks painted 

with a flat black paint. Fry up to 3 weeks of age showed 

a marked preference for extremely bright light (7,800 

lux), by week 9, most juveniles preferred lower (2-4 

lux) light intensities (Bulkowski and Meade 1983). 

Corazza and Nickum (198 1) observed greater fry 

dispersal in tanks with gray walls than in tanks with 

white, yellow, or green walls. A dffuse light source 

may beneficial. 

Turbid water (Bristow and Summerfelt 1994) does an 

exceptional job of dispersing the fry (Figure 8). In tanks 

with turbid water, fry are concentrated near the surface, 

but dspersed horizontally, in clear water, fry have a 

greater vertical distribution, even going to the bottom of 

tanks with black lateral walls but gray-colored bottom. 

The horizontal dispersal of fry in turbid water seems to 

be the consequence of the light-scattering effect of 

turbidity which reduces the amount of light reflected 

from the tank walls, thereby eliminating fry attraction 

to the tank walls. Turbidity also reduces cannibalism, 

perhaps because cohort encounters are reduced inasmuch as the fry are more evenly distributed throughout 

the tank. Loadman et al. (1986) suggested that cannibalism may be reduced when fry are Qspersed throughout 

the water column. 

NCRAC Culture Series 101 - Walleye Culture Manual 171 
Figure 8. Comparison of larval behavior in clear (left) and turbid (right) water 

culture. Fry in tanks with clear water are attracted to reflected light from the 

sides of the culture tank. In turbid water the light scattering effect of the 

suspended clay particles diffuses the light and fish are distributed across the 

tanks. (Used with permission, Journal of the World Aquaculture Society). 

eat. Perhaps it improves contrast 

between the brownish-orange feed 

and the milky gray color of the 

turbid water, or because the lightscattering effect of the turbidity 

may have better illuminated each 

feed particle (i.e., some light 

would be reflected on all sides of 

the feed particle as opposed to 

only the top half in clear water), 

thus increasing the ability of the 

fry to see the feed. Visual stimuli 

are said to be important for 

successful feeding of walleye 

(Rottiers and Lemm 1985). 

Corraza and Nickum (1 98 1) 

observed that the phototactic 

behavioral response of walleye 

larvae exceeded the response to 

all other stimuli short of drect 

physical contact. Nonfeeding 

would be expected of larvae that 

are clinging to the walls of the 

culture container, or in walleye that had not inflated 

their gas bladder. Reasons given for nonfeeding in 

previous experiments is inexplicable, however, transparency of the water may have been a major factor 

Cannibalism 

Walleye are predaceous fish, consuming zooplankton, 

aquatic insects, and fish in that order as they grow from 

first-feeding to juveniles in ponds. Cohort cannibalism 

is the name given to sibling 

cannibalism, where fry of 

about equal size attack each 

other (Loadman et al. 

1986). Most mortality from 

cohort cannibalism occurs 

from trunk attacks, not the 

result of successful 

consumption of the prey, 

(Figure 9). Cannibalism 

begins as soon as the fry 

begin feeding (Howey et al. 

1980) and it can be a major 

factor in total mortality 

when fish are not feedmg 

(Olson 1974). 

Non feeding 

Early reports of nonfeeding by larval walleye raised in 

intensive culture were commonplace: “Typically, many 

of the walleye fry never showed any interest in the 

food” (Beyerle 1975). Nonfeeding fish and cannibalism 

were considered the major problems for intensive 

culture of walleye (Howey et al. 1980). The problem 

was related to color or palatability of the feed, or 

inadequate particle density, 

but success with brine shrimp 

was sometimes poor also. FV 

distribution within the rearing 

tank may also affect the 

opportunity of fry to encounter and consume feed 

particles. Bristow and 

Summerfelt (I 994) reported a 

major difference in feed 

acceptance of fry on the 7th 

and 14th days in turbid water 

compared to clear water tanks 

(Table 2). 

It seems that turbidity 

improved the ability of larval 

walleye to distinguish and 

Table 2. Age when walleye begin feeding for fish raised in clear (0.4 NTU) 

and turbid (23.8 NTU) water (Bristow 

and Summerfelt 1994)’ 

Fry (“h) with food in gut 

Days posthatch Clear Turbid which is from the tail first 

4 0 6 

7 13.3 94.7 

14 90.7 98.7 

21 98.7 100.0 

NTU is nephelometric turbidity unit. 

172 NCRAC Culture Series 101- Walleye Culture Manual 
. Stocking 

Feeds, fccdcrs and fccding 

. Tank hygicnc 

. Watcr quantity and quality 

Culture tanks 

Searly all possible tank shapcs 

have bccn investigated for fry 

<%'@ culture. Barrows et al. (I 988) 

dcscri bcd a tan k- w i thi n-a- tan k 

made up with an inner 22 gal (83- 

L) plastic trash container subFigure 9. A chain of 10-day-old walleye fry feeding on similar-sized siblings merged in a 55 gal (208-L) 

(photo by B. T. Bristow). 

Cannibalism in intensive culture of walleye to 21 -d 

posthatch differs among stocks: 3.4-5.4% for stocks 

from IA, KS, and OH, but 10.5 to 17.6% from ND, WI, 

and MN (Heys et al. 1996). Thus, certain wild stocks 

that exhibit an inherent tendency to cannibalize should 

be avoided also. It is important to avoid stocking fish 

that differ by more than 1-day of hatching. Fish hatched 

on separate days and fish from different stocks often 

have different initial lengths (Hey et al. 1996). It has 

long been known that fish-size dfferential in walleye 

populations increases cannibalism (Nickum 1978; 

Howey et al. 1980). Fish that differ by more than 1-day 

in age would have a size advantage over younger fish 

that may be sufficient to induce cannibalism. 

Cannibalism can be avoided by feeding frequently with 

adequate amounts and appropriate sizes of a quality 

feed. Loadman et al. (1 989) recommended a particle 

density of formulated feed close to 1 OOL. Cannibalism 

is reduced in turbid water culture (Bristow and Summerfelt 1994; Bristow et al. 1995), perhaps because fish 

accept formulated feed sooner than in clear water 

(Table 2). 

Basic methodology 

Intensive culture of walleye from hatch to a small 

fingerling requires provisions for biological characteristics of the species and environmental factors: 

Culture tanks: size, shape, and color. 

Screens 

Surface sprays 

9 Aeration and pumping 

9 Light and temperature 

9 Turbid water culture 

fiberglass barrel. The purpose of 

the design was to obtain an 

upwelling distribution of water. An 11 &in (30-cm) 

stainless steel screen was attached to the top of the 22 

gal (83-L) inside container for an outlet screen. The 

double-tank was designed to obtain an upwelling 

current and circumferential ring of micropore tubing 

was used to keep fry from impinging on the screen. 

Another upwelling design was described by Kindschi 

and MacConnell (1989). Conical-bottom tanks were 

used to separate feed and fecal material from the 

rearing area, but fry were contained within a removable 

12 mesh/cm (472 pn) aluminum screen basket of 65-L 

volume. 

Loadman et al. (1989) described a cuboidal tank with a 

flow pattern that was designed to keep the feed in 

suspension and maintain a high particle density. That 

design was not as effective as circular tanks, however 

(Barrows et al. 1993b; Moore et al. 1994a). The three 

case studies for this chapter provide a diversity of tank 

shapes and operations including rectangular fiberglass 

tanks (Colesante 1996), cylindrical (circular) fiberglass 

tanks (Moore 1996), and trough-shaped tanks with an 

upwelling current (Moodie and Mathias 1996). 

Clinging of fry to the sidewalls of the tank will affect 

success of the culture system. The clinging behavior is 

a function of tank size, color of the tank walls, light 

intensity, and turbidity. Fry are strongly attracted to 

light, drect or reflected light. They will cling to the 

sidewalls, screens, and they are even attracted to the 

bottom of the tank in tanks with black sides but light 

colored, bottom. Their presence on the bottom results in 

some loss of fry when they are siphoned up in process 

of cleaning the tanks. 

NCRAC Culture Series 101 - Walleye Culture Manual 173 
Tank size is another factor affecting clinging. A greater 

percentage of the stock cling to the sides of smaller than 

larger tanks because the lateral area (ft’, m’) per unit of 

tank volume (ft3, m’) of tanks walls of smaller tanks is 

larger than that of larger tanks. Also, in culture water 

with low turbidty (<lo NTU), the &stance from tank 

side walls to locations in the tank away from the sides 

will increase beyond the reaction distance of the fish 

and a smaller percentage of the population will be 

attracted to the tank walls. The 179 gal (679-L) tank 

(1 23 cm across the top, and 109 cm across the bottom, 

and 76 cm deep), used by Moore et al. (1994b) and 

Moore (1996) is a desirable size. Moore et al. (1994b) 

obtained 74.9% survival to 21 days with 99.5% GBI 

when this tank was stocked at 20L 

Colesante (1 996) reports that darkened sides of the 

rearing tanks minimizes clinging behavior; and highintensity lights help achieve uniform hstribution of fry, 

and attracts the fry to the surface to aid in the process of 

gas bladder inflation. Corazza and Nickum (1 98 1) 

observed improved larval dispersal in tanks with gray 

walls compared with tanks with white, yellow or green 

walls. A diffuse light source and a flat black or gray 

tank color is helpful to reduce reflection of the light 

from the tank walls. Survival in my laboratory was 

generally poor results until turbid water was used 

(Bristow and Summerfelt 1994). Artificial turbidity was 

developed by addition of a small volume of a clay 

slurry. With turbid water, clinging behavior is avoided 

and tank color does not matter. Some hatcheries have 

naturally turbid water (2 15-25 NTS) from colloidal 

clay (particle sizes 12 mm) that is not removed by rapid 

sand filtration. 

Screens 

Whatever form of the standpipe or drain system, it must 

be equipped with a screen to retain the fry, but in 

feeding formulated feed, it is important to use the 

largest mesh size possible to keep the screens from 

clogging, even if feed is lost through the screen. The 

same problem occurs with feeding live food. The 400 

pn FFK (particle range 240-675 pn [Loadman et al. 

19891) and brine shnmp nauplii, 200 to 250 pn will 

pass through the smallest mesh needed to retain fry. 

Colesante et al. (1986) used screens with openings of 

200 pn to reduce loss of brine shrimp nauplii. Barrows 

et al. (1988) used a 600-pn-mesh stainless steel screen. 

In 1988 I used stainless steel fabric with 0.380 pn 

mesh and 30% or 36% open area, but that retained too 

much waste feed and caused fouling; in 1989, a mesh 

size of 0.704 width of opening and 44.2% open area 

was used (Summerfelt 1990). Three- to 5-d posthatch 

fry were retained by screens not larger than 710 pm 

(1 0.3 1 mesheskm) between threads and no more than 

53% open area (Kindschi and Barrows 1991a). Of 

course, fry grow in length between hatching and 3-days 

but depth of body decreases with yolk sac absorption, 

so the same 710 pm screen seems to retain newly 

hatched as well as 3-day-old fry. 

Since the 1990 culture season, the drain in our culture 

tanks has been surrounded by 6-in (152 mm) PVC pipe 

which has large areas of PVC cut away, the cut-away 

sections are covered with square-weave, monofilament 

nylon (NitexTM, Tetko, Inc., Briarcliff Manor, New 

York). After cleaning the PVC with PVC cleaner, the 

fabric is attached to the PVC pipe with PVC pipe glue. 

The fabric needs to be held in place for about a minute, 

but then it bonds tightly. In the first 21-d posthatch, 710 

pn mesh screens are used; after 21 days posthatch, a 

second set of screens with 1,000 pm (1 mm) mesh with 

58% open area to improve effluent flow. To prevent 

accidental use of the 1 mm mesh when fry are first 

stocked, the top rim of the pipe with 1000 pn screens is 

painted red. Fry size at hatching varies with the stock, 

but the smallest size fry we have encountered are those 

produced by out-of-season spawning. A few of those fry 

were small enough to pass through the 710 pn mesh. 

Surface spray 

Moore et al. (1994a) reviewed GBI for seven studes on 

intensive culture of walleye fry, the most recent 

reference was 1991. Data given in that review for GBI 

for 23 trials ranged from 10 to 93.9%, with a mean of 

42.1% (95% confidence interval of 30.3-53.9). Thus, 

GBI was typically poor until it was discovered that a 

spray of water to the surface would enhance gas bladder 

inflation (Barrows et al. 1993b; Moore et al. 1994a). 

Barrows et al. (1 993b) reported 98.4% gas bladder 

inflation (GBI) in tanks with a spray and 51.7% GBI in 

tanks without a spray. Moore et al. (1994a) obtained 

89% GBI in circular tanks with spray and 62% in tanks 

without a spray. In another study, using sprays on all 

tanks, Moore et al. (1994b) obtained 98.5 to 100.0% 

GBI in nine fry density trials with survival as high as 

64.1 %. Although Howey et al. (1980) found that 20% 

of walleye raised on brine shrimp and daphnia did not 

have an inflated gas bladder, seemingly, walleye fed 

brine shrimp during the interval of gas bladder inflation 

174 NCRAC Culture Series 101- Walleye Culture Manual 
inflate their gas bladders 

without a surface spray 

(Colesante 1996). 

The spray removes the 

oil film and cleans the 

surface of feed and 

debris (Figure 10). In 

circular tanks with a 

circular flow pattern, the 

water passes under the 

spray head with each 

revolution of the water 

mass. The critical 

volume of flow needed 

for an effective spray 

has not been determined: Moore et al. 

(1994a) used a flow rate 

of 0.3 to 0.5 Wmin 

through the spray head 

and Bristow and 

Figure 10. Sketch designed to explain how a surface spray 

works to clear oil from the water surface of a fry culture tank. 

The spray is a 180' perimeter nozzle (inset). 

the water is delivered to 

the culture tanks. 

Compressors should not 

be used to aerate water 

destined for use in 

intensive culture of fry 

because they often 

contaminate the air with 

oil in the compression 

cycle. Compressed air 

contaminated with oil 

that is bubbled through 

water will transfer the 

oil to the water. The oil 

will rise to the surface 

and interfere with gas 

bladder inflation. 

Submersible pumps 

should also be avoided. 

They often leak minute 

quantities of oil, but 

when a seal breaks, the 

Summerfelt (1 994 j used 1 L/min. It seems important 

for the spay to impact the surface with enough pressure 

to produce a slight depression in the water under the 

spray (Figure 11). The sprayer is a 180" perimeter 

nozzle (A. H. Hummert Seed Co., Inc., St. Louis, 

Missouri) and it is directed at a 80-90" angle with the 

water surface from a distance of not more than 20 cm 

pump releases a large volume of oil. To avoid contamination of fry culture tanks with even small quantities of 

oil, water should be pumped with centrifugal, axial flow 

or peristaltic pumps. 

A column of rising air bubbles in a fry culture tanks 

may cause turbulence, and fast rising air bubbles will 

above the water surface. 

The number of sprayheads needed per 1,000 

cm2 of tank surface has 

not been critically 

evaluated, but Moore et 

al. (1994b) observed 

slightly higher GBI in 

tanks equipped with one 

spray per 5,941 cm2 

(GBI values were 99.5, 

99.5, and 100%) 

compared with tanks 

with one spray per 4,778 

cm2 (GBI values were 

88.7, 96.3 and SS.O%j. 

Aeration and pumping 

Degassing and aeration 

of the water supply 

should be done before 

throw fry out of the 

water where they will 

stick to the side walls 

above the water line. 

Barrows et al. (1988) 

used a curtain of small 

air bubbles from 

micropore tubing to 

prevent fry impingement at the water outlet. 

In some hatcheries, an 

air line is placed around 

the center standpipe to 

keep fry from being 

impinged on the screen. 

A large surface area of 

the screen reduces 

current velocity. Also, if 

Figure 11. Small (150 L), experimental fry culture tank that 

shows the trough formed in the water surface by the impact 

of the surface spray operated at a flow rate of 1 Umin. 

NCRAC Culture Series 101 - Walleye Culture Manual 175 
screens are painted black, fry attraction to reflected turbidity seems to reduce the amount of light reflected 

light will be reduced. from the tank walls. The clinging behavior of walleye to 

the sidewalls of the culture tanks was greatly reduced or 

Light and temperature 

Research findings on light intensity are varied. It seems 

that fluorescent lights, flood lamps, and natural light at 

intensities of 100 to 700 lux are acceptable. Colesante 

(1996) uses high-intensity lights that produce 680 lx at 

the water surface; and Moore (1 996) recommended 500 

lux. Diffuse lighting is often recommended to distribute 

fry and to deter fry from clinging to the sides of the 

tank. However, light is a necessity. Fry do not feed in 

the dark. 

The minimum water temperature should be 55°F 

(1 2.8"C) (Colesante 1996). Moore (1 996) reported that 

feed acceptance and survival is greater at 65°F (1 8.4) 

than at 55°F (12.8"C), and an ideal temperature range is 

6045°F (15.6-18.4"C), with 65 (18.4"C) as optimum. 

Moodie and Mathias (1996) maintain a temperature of 

68°F (20°C) throughout. Moore (1996) stimulates fry 

feeding by a sudden increase of 9°F (5°C) for 24-h 

when fry were 5 d posthatch. I also use a temperature 

rise to stimulate feeding, but a somewhat different 

regimen: the temperature is slowly increased from 

incubation temperature to about 59°F (15°C) by the 4th 

eliminated in turbid water. 

Survival is increased, the fish are on feed sooner; their 

weight at 21 to 30 d posthatch was 200 to 300% larger 

than weight of fry raised in clear tanks (Bristow and 

Summerfelt 1994). In all of the six comparisions of 

larval performance in clear and turbid culture since 

1993, the fish in turbid grew substantial faster than fish 

in clear water (Figure 13). 

Turbi&ty is defined as "an expression of the optical 

property that causes light to be scattered and absorbed 

rather than transmitted in straight lines through the 

sample" (APHA et al. 1989). In ponds, turbidity is 

caused by suspended inorganic matter (clay, silt, finely 

divided organic matter), soluble organic compounds, 

and phytoplankton. Suspended solids are defined as 

"the residue retained on a glass fiber filter dried to a 

constant weight at 103-105°C" (APHA et al. 1989). 

Typically, there is a strong relationship between the 

concentration of suspended solids and turbidity (Lloyd 

et al. 1987). 

day, feeding is started and the 

temperature is increased about 5°F 

(23°C) to 63.5"F (17.5"C); it is not 

reduced in the 24-h, but 

incremented slowly over the next 

25-d to about 20°C at 30-d posthatch (Figure 12). Walleye typically 

grow about 0.67 mdd in the first 

30-d (7.5 mm at hatch to 27 mm in 

30 days) 

Turbid water culture 

Survival, length, and weight of 

larvae raised in turbid water to 21 - 

30 d were significantly greater than 

for larvae raised in clear water 

(Bristow and Summerfelt 1994). 

212 1 

2o i 

3 181 c1 

!!! 17 

16 

a / 

/ i 

141 

\ Feeding started 

Larvae were more evenly &stributed in the turbid water than in clear 13 

water (Figure 8). The turbid water 0 4 8 12 16 20 24 2830 

was milky gray. In turbid water, Days posthatch 

Figure 12. Sample temperature ("C) profile of the temperature regimen used to 

coincides with initiation of feeding.The goal is to reach 20" C by the 28th day. 

larvae &d not congregate on the 

tank 

The light-scattering effect of 

as they did in water- raise walleye fry hatch to 30 d posthatch. The sharp increase on the 4th day 

176 NCRAC Culture Series 101- Walleye Culture Manual 
Figure 13. Comparison of 30-day-old juvenile walleye raised in clear (top) and 

turbid (bottom) water.The mean total length (weight) for fish raised in turbid 

water was 27.4 mm (0.16 g) compared with 15.0 mm (0.02 g) in clear water. 

The system described by Bristow and Summerfelt 

(1994) to supply a clay-slurry for six, 40 gallon (150-L) 

tanks has been enlarged for use with six, productionscale (264 gal; 1,000 L) tanks (Figure 14). The clay 

slurry (8 g of clay per L) is stirred with a commercial 

mixer with a $4-hp motor that turns a shaft at 1,725 rpm. 

The clay slurry is distributed with a %hp pump that has 

a calibrated flow of 38 gpm with 10 ft of head. To attain 

a turbidity level of 50 NTUs in a 1,000 L tank would 

requires addtion of clay slurry every 20-minutes 

(Figure 15). To avoid running the clay-slurry tank dry, 

the setup is designed to not pump more than 144 of the 

600 L capacity of the clay-slurry tank per day. The 

mixer runs continuously, and the pump distributes 2 L 

of stock every 20 minutes, 72 times each day. For a 

single 1,000 L, it would require about 3.3 lb (1,500 g) 

of clay per day. To supply more culture tanks with the 

same system, the concentration of the clay slurry should 

increase proportionally, but the mixer and pump can 

handle at least six, 1,000 L tanks. 

Stocking density 

Populations of yolk sac fry (prolarvae) shipped in 

plastic bags to the culture site will often experience 

high mortality after stocking, which is a major contrast 

to stocking fry that are hatched on site, because 

substantial mortality in these populations rarely occurs 

until the critical period in the late postlarval II stage 

(Figure 2). Although shipment of eggs may result in 

some egg mortality, it is better that the mortality take 

place in the hatching jar rather 

than the culture tanks because 

dead fry liberate oil from their 

oil globules (Boggs and Summerfelt 1996). Colesante and 

Schiavone (1980) attributed 

mortalities that occurred in the 

first 36-h after transporting 

walleye fry in plastic bags to 

suffocation of the fry in the 

bottom layers and corners of the 

bags, especially after the bags 

were tempered in holdmg 

troughs. The mortalities increased in relation to the length 

of time the bags are left stationary rather than to fry densities in 

the bag. We have observed 

substantial mortalities in the first 

few days after stockmg fry that 

were transported to our facility in plastic bags, but not 

in with fry that were hatched on site from eggs that 

were shipped (Figure 2). Mortality normally peaks at 

17- to 19-d posthatch at 19-20°C when non-feeding fry 

starve. 

Mixer 

Return line 

fi== 

d 

Pump 

To culture tanks 

Figure 14. Design of a clay-slurry tank and distribution system for intensive culture of walleye fry in 

turbid water. 

NCRAC Culture Series 101 - Walleye Culture Manual 177 
Figure 15. Experimental fry culture tank (150 L) showing injection (upper left 

corner) of a clay slurry that is used to maintain turbid water (50 NTU). 

Fry for stocking should be from those collected in the 

fry catch-tank that hatched within a short time interval, 

preferably within 12 hours, but not more than 24 hours. 

The fry are removed from the catch tank and placed in 

another holding tank for 2-3 days with low water flows 

before stocking the culture tanks. 

Enumeration of fry for stocking can be done by hand 

counting, volumetrically, gravimetrically, or by an 

electronic counter (Kindschi and Barrows 1991b). The 

counter can count 500,000 fry per hour with an average 

error of 3%. They found that gravimetric methods were 

more accurate than volumetric estimates, which have 

been the standard hatchery procedure. 

Recommendations for stockmg density (number of fry/ 

L) for large-scale production of walleye fry in intensive 

culture varies from 21 (Colesante 1996) for fry started 

on brine shrimp, to 40 (Moore 1996) and 56 (Moodie 

and Mathias 1996) for fry fed formulated feed. With 

improvements in survival, stockmg densities of 80 to 

100L may result in excessive fry density before 30- 

days are reached, and problems may develop with poor 

water quality and disease (bacterial gill disease and 

columnaris disease) causing unnecessary mortality. 

Feeds, feeders, and feeding 

The development of formulated feeds for fry (“starter” 

feeds) is reviewed by Barrows and Lellis (1996). Early 

efforts in feeding formulated feeds 

quite naturally included trout and 

salmon feeds (Beyerle 1975), but 

all early efforts at feeding formulated feed were unsuccessful 

(Nickum 1978). The U.S. Fish and 

Wildlife Service W-series diets 

developed at the Spearfish facility 

were the most common. The W- 16 

formulation was the latest in that 

series. When added to the culture 

tank, rings of oil sheen were 

visible; perhaps the oily surface 

film that inhbited gas bladder 

inflation was the reason for poor 

performance on this diet rather 

than the composition and proximate analysis. Barrows et a1 

(1988) used a feeding ring to 

confine the surface film from the 

feed to a portion of the water 

surface. A feeding ring is not needed with use of a 

surface spray. Feed size, color, and texture have been 

considered the most important factors affecting acceptability. Failure of the fish to feed or dgest the feed has 

been cited frequently as a major factor in the failure of 

walleye culture on formulated feeds. 

The FFK B-series (€3-400 and B-700) feeds (Biokyowa 

Inc., Chesterfield, Missouri) have been used by more 

investigators than any other for feeding fry formulated 

feeds (Kindschi and MacConnell 1989; Moodie and 

Mathias 1996; Moore 1996). In 1996, the FFK B-series 

cost $40.86/1b ($89.89/kg) plus delivery charge. 

However, it is not necessary to keep fry on the B-series 

for more than 7 d, a “phase” feeding strategy proposed 

by Barrows et al. (1993b) can be used. Fry can be 

started on the B-series then weaned to the FFK C-series 

or other feeds without loss of performance and with 

76% less feed cost per fish produced than for fish kept 

on FFK-€3 for 30-d posthatch (Barrows et al. 1993b). 

There is no concensus on the amount of formulated 

feed to feed walleye fry during the first 30 days. 

Typically, fry are started on FFK-B series (B-400), 

followed by either the E-700 (Moore 1996) or C-700 

(Moodie and Mathias 1996).The kinds and amounts of 

FFK feed that we have found useful are given in 

Table 3. 

178 NCRAC Culture Series 101- Walleye Culture Manual 
Fish feeders found at most 

hatcheries are for dispensing 

much larger quantities of 

feed than used in fry culture 

system; they are not sufficiency precise for feedmg 

small quantities of fry feed 

accurately and consistently to 

prevent food deprivation or 

excessive feeding and tank 

fouling. McCauley (1 970) 

developed a scraper feeder 

using a clock mechanism. 

Many researchers have used 

vibrator feeders to dispense 

fry feed (Loadman et al. 

1989; Summerfelt 1990), but 

the amount of feed the 

Table 3. ISU guidlines for feeding fry. 5 minutes for intervals of 

less than 1 second. 

Length Quantity Ratio 

(mm) (g/1 000 fry) (B400/C700)a 

<11 

1 1-1 2.9 

13-1 4.9 

15-1 6.9 

17-1 8.9 

19 -20.9 

21 -22.9 

223 

5.0 

5.8 

7.3 

8.5 

10.1 

11.9 

13.6 

15.0 

1oo:o 

7525 

50:50 

2575 

0:lOO 

C700:WG9206 

7525 

50:50 

100% 

aB400 and C700 are FFK-series 

WG9206 is the walleye grower diet 

feeders dispense at each feeding could not be regulated 

with accuracy or consistency (Loadman et al. 1989). 

Moodie et al. (1 992), and Moodie and Mathias (1 996) 

used custom made, precision feeders that are not 

available commercially. The feeder used by Moore et al. 

(1994a, 1994b), Bristow (1994), Bristow et al. 1996), 

and Moore (1996) is a custom-made auger feeder 

(Northland Aquaculture, Inc., Ames, Iowa) that delivers 

small amounts of feed accurately and consistently 

(Figure 16). Timers must be capable of turning on every 

Feeding rates and feeding 

frequency are important for 

successful fry culture. 

Feedmg should be at 3-5 

min intervals at least 22-h/ 

day. Feeding should be 

stopped only to clean the 

tanks. Survival has been 

poor when feeding was 

stopped for more than an a 

6-h interval per day. 

Tank hygiene 

In feeding formulated feed, 

tanks must be cleaned at 

least once per day. During tank cleaning, the inflow is 

not turned off to avoid forgetting to return the flow. The 

bottom with food, debris and dead fish is siphoned out. 

A siphon hose is inserted between the screen and 

standpipe to lower the water halfway to allow wiping 

growth from the sidewalls of the tank; the wiping stroke 

is upward to facilitate removal of the scum from the 

walls and to avoid contaminating the culture water. 

When needed, the sidewalls are wiped to the bottom to 

remove accumulation of scum. Providing that water 

level is still sufficiently below the outflow level of the 

standpipe, the screen is removed and 

washed in warmwater with a spray and 

replaced. Other variations in tank cleaning 

procedures are given in the case studies. 

Figure 16. An auger feeder used to dispense precise quantities of feed 

for feeding fry in small and production-scale tanks (Moore et al. 1994a 

and 199413). Figure courtesy of Northland Aquaculture, Inc., Ames, 

Iowa. 

Wafer flow 

Before walleye fry begin feeding (Le., 

prolarvae), inflows are regulated to obtain 

0.5 exchanges per hour. Once feeding 

begins, the exchange rate is increased to 

0.75 exchanges per hour and eventually to 

1 .O exchange by 21 -days. Higher flow 

rates are recommended by others (Nickum 

1978). Although high flow rates may be 

necessary to obtain desirable water quality, 

high exchange rates imply higher current 

velocities which may overtax the swimming ability of the fry and deplete their 

energy resources. 

NCRAC Culture Series 101 - Walleye Culture Manual 179 
Water quality 

Poor water quality causes stress and mortality, and 

reduces growth. The reduction in water quality which is 

sufficient to stress fish often increases the risk of 

bacterial gill diseases and catastrophic loss of fish, even 

if it does not have an immedate impact on production. 

The water quality parameters of primary concern are 

dssolved oxygen (OJ, ammonia (NH,), nitrite (NO;), 

carbon dioxide (CO,), and gas supersaturation from 

either oxygen (0,) or nitrogen (NJ Dissolved oxygen 

should not be less than 5 ppm, preferable near saturation, but oxygen supersaturation should be avoided. 

Recent observations suggest that walleye fry are 

especially sensitive to supersaturation (Summerfelt 

1990). In 1995 culture season, high mortality of walleye 

fry occurred in tanks supplied by surface water pumped 

from a pond that had supersaturated oxygen (Tom 

Harder, Max McGraw Wildlife Foundation, personal 

communication). When the problem reoccurred in the 

spring of 1996, it was resolved by passing the inflow 

through a degas column (pipe packed with plastic 

media, but open on both ends) into an extra tank; the 

water from that tank was pumped to the culture tanks. 

The problem seems similar to large &urnal swings in 

total gas pressure (AP) observed in ponds used to 

produce channel catfish and bluegill without artificial 

aeration (Boyd et al. 1994). Boyd et al. (1994) found 

that diurnal changes resulted primarily from DO 

supersaturation produced by phytoplankton; DO 

increased from a mean of 67.7% (AP -40 mm Hg) of 

saturation in the morning to a mean of 158.9% (AP, 1 11 

mm HG) in the afternoon, with an exceptional value of 

343.6% saturation. Thirty-four percent of afternoon 

values exceeded AP 115 mm Hg, pressure known to 

cause mortality during continuous exposure bioassay. 

Upper limits for continuous exposure to the common 

metabolites (ammonia, carbon &oxide, nitrite), pH, and 

chlorine should not exceed general standards for fish 

culture as given by Piper et al. (1982) and Meade 

(1 989): 

unionized ammonia 

carbon &oxide <10 pprn 

nitrite 

< 0.0125 to 0.02 pprn 

0.1 ppm in soft water, 0.2 ppm 

in hard water 

PH 6.5-8.0 

These values are guidelines, they should not be interpreted to mean that concentrations slightly above the 

guidelines will be lethal. Toxicity will change with the 

age, temperature, pH, alkalinity, turbidity and other 

factors. Because walleye fry have been too difficult to 

raise in experimental systems, relatively little information is available on their sensitivity. However, Nickum 

(1978) stated that walleye fry “seemed to be unusually 

sensitive” to traditional chemical therapeutic agents. 

High (2 9.8) pH may be lethal to walleye in the absence 

of ammonia (Bergerhouse 1992), but pH as low as 28.3 

(i.e., OH- ions) shifts the equilibrium of ammonia to the 

unionized form (NH,) that is more toxic to fish 

(Thurston et al. 1981): 

NH, + H,O # NH,+ + OH 

Bergerhouse (1992) reported that in the absence of 

ammonia, mortality of 3-d-old walleye fry in a 6-h 

exposure was 37% at a pH of 10.3 and 100% at a pH of 

10.5. However, mortality to 4-d-old fry was 100% after 

only 4-h exposure to pH 10 in the presence of 0.98 mg/ 

L of unionized ammonia. Bergerhouse also found that 

12-d-old fry were more sensitive than 3-d-old fry to pH. 

Bushman (1992) observed that pH values 2 8.3 reduced 

gas bladder inflation of larval walleye. Sudden changes 

in pH may occur when fry received in plastic bags are 

transferred to culture tanks. It is important to recognize 

that pH is a log scale, therefore, 1 unit decrease in pH 

(8 to 7) is a 10 fold increase in hydrogen ions. A pH 

change of 0.8-1.0 pH unit caused total mortality to 

striped bass larvae (Doroshev 1970). Water of very low 

alkalinity (< 10 ppm) is poorly buffered and may show 

undesirable pH fluctuations. 

Tolerance of walleye for highly alkaline waters is not 

known. Obviously, the water supply should not be 

contaminated with pesticides, PCB’s, heavy metals 

(mercury, lead, zinc, cadmmm), chloramines, or free 

chlorine, or toxic residues from toxic paints or sealants. 

Case studies 

The case studes by Colesante (1996), Moode and 

Mathias (1996), and Moore (1996) that accompany ths 

chapter provide contrasting strategies for productionscale intensive culture of walleye fry. Colesante uses 

brine shrimp for 30 days, followed by 14 days of mixed 

feedmg brine shrimp and formulated feed; Moodie and 

Mathias and Moore use only formulated feed. Moodie 

and Mathias use a unique trough and recycle system for 

180 NCRAC Culture Series 101- Walleye Culture Manual 
fry culture; Moore uses standard circular tanks with a 

central drain; Colesante uses rectangular tanks. 

Colesante does not report a problem with NGB but he 

describes some precautions undertaken to avoid the 

problem. Moore uses surface sprays to prevent NGB. 

Moodie and Mathias reported occurrence of the NGB 

problem with their system. To reduce the problem, they 

added much larger volumes of “new” water to the 

culture system when gas bladder inflation was taking 

place to remove surface oils during the period. However, they have had gas bladder inflation rates of only 

16 to 23% in the production scale tanks. Stochng 

densities, fry& of 21 (Colesante), 40 (Moore) and 56 

(Moodie and Mathias) are used. 

Acknowledgments 

support for my research on tlvs topic has been 

provided by the USDA under the auspices of the North 

Central Regional Aquaculture Center, the Iowa Department of Natural Resources, and the Iowa Agriculture 

and Home Economics Experiment Station (project 

2982). I am pleased to acknowledge the collaboration of 

Gary Marty on studies of gas bladder inflation. Foremost, I am grateful to several graduate students whose 

thesis and dssertation research contributed so much to 

development of walleye fry culture: B. T. Bristow, R. P. 

Bushman, K. L. Kuipers, T. A. Phillips, P. W. Rieger, 

and C. Stettner. I am also grateful to R. D. Clayton for 

many forms of assistance, and to the many undergraduate students who have provided indspensable assistance 

in the daily routine of the fish husbandry and water 

quality analysis. Rex Heer did the drawings for Figures 

4, 7, 8, and 10. R. Clayton prepared figure 14. 

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NCRAC Culture Series 101 - Walleye Culture Manual 185 
186 NCRAC Culture Series 101- Walleye Culture Manual 
Moodie, G. E. E., and J. A. Mathias. 1996. Intensive culture of larval walleye on formulated food. 

Pages 187-190 in R. C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. 

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

Intensive Culture of Larval Walleye on 

Formulated Feed 

G. Eric E. Moodie, Department of Biology, University of Winnipeg, Winnipeg, Manitoba, R3B 2E9 CANADA 

and John A. Mathias, Department of Fisheries and Oceans, Freshwater Institute, 50 1 University Crescent, 

Winnipeg R3T 2N2 CANADA 

Introduction 

we developed a commercial scale culture system for 

raising walleye on formulated feed from the egg to 

fingerling stage, which makes efficient use of space and 

labor. The main obstacles to the commercial production 

of walleye larvae in the past have been the inability to 

successfully start large numbers of larvae (35,000- 

40,000) per rearing unit, failure of the fish to inflate 

their swimbladder during the first few days after 

hatching, and variable survival when using formulated 

feed. The critical requirements for a successful system 

are constant suspension of food particles, because 

walleye larvae will not feed from either the tank bottom 

or the water surface, conditions that allow the larvae to 

gulp air at the surface during the process of 

swimbladder inflation, and the use of high quality 

feeds. 

bottom. Water flowing through the holes produces an 

upwelling current. Water exits from the trough via five 

screened boxes, located along one side of the unit above 

the inlet pipe (Figure 1). Each screen has a surface area 

of about 8.1 ft2 (0.75 m2). Mesh size of the screen is 500 

pm. The purpose of the large screen surface is to reduce 

water velocity around the trough outlets. This results in 

minimal suction on larvae and food particles. Placement 

of the screens along one side of the trough reduces their 

influence on upwelling current patterns. The boxes are 

removable and can be opened to allow thorough 

cleaning. Precision feeders are designed to supply 

precisely controlled amounts of 400 pn diameter feed 

at specified time intervals. 

Other components of the system include: a waste 

particle remover, biological filter, inline electric heater, ~ - - ___. 

and aeration tower. The relationship of all components 

are shown in Figure 1. These components (minus the 

Methods 

The culture system (Figure 1) we 

developed to meet these criteria 

heater 

consists of a 21 x 2.7 ft (6.4 x 

0.82 m) trough with 

vertical, upwelling water 

currents; removable, 

oversized outlet screens; 

and a system of automatic, 

precision feeders. The unit 

is filled with 91.8 ft3 (2.6 

m3) of water. Water is 

supplied through a polyvinyl chloride (PVC) pipe 

perforated with a row of 

0.06 in (1.5 mm) diameter 

holes. The pipe runs the 

length Of the trough, 

one side and near the 

Figure 1. Larval rearing system components. Arrows indicate direction of water 

flow. Proportions not to scale. 

NCRAC Culture Series 101 - Walleye Culture Manual 187 
Chapter 7 - Intensive Culture of Walleye Fry 

screen boxes), together with additional tanks, are also 

used for juvenile grow-out after 30 d. 

The rate of water flow to the trough is critical; although 

an upwelling flow is necessary to prolong the suspension of food, excessive water velocities are detrimental 

to the larvae. In our design, water exchange in the 

trough and water velocities within the trough can be 

varied independently within limits. Water exchange rate 

and velocities are kept relatively low before the larvae 

begin feeding. After feeding begins, we increase the 

exchange rate and water flow, to achieve a velocity of 

about 3.1 ids (8 cds) at the surface. 

Waste water from the trough flows by gravity to a 

particle separator. Water is then pumped to an inline 

water heater from which it flows by gravity through a 

6.6 ft (2 m) oxygenation tower and a down-flow, 

submerged-medmm biofilter. The tower contains a 

series of internal baffles designed to restore the oxygen 

content of water to about 94% saturation or about 8.4 

ppm (8.4 mgL) at 68°F (20"C), at a flow rate of 35 

gpm (1 32 L/min). Water from the oxygen tower is 

collected in a small reservoir, from which it is pumped 

back to the trough. This pump is required to produce 

the pressure necessary to circulate water in the trough. 

The system is backed up by alarms that can be triggered 

by inappropriate water temperatures, low water levels, 

or a pump failure. Aeration with compressed oxygen is 

available in case of electrical or pump failure. 

We believe that in any intensive culture system good 

hygiene is crucial to success. This is achieved through 

the use of water from deep ground wells and disinfection. At the start of each season, the entire system is 

treated with a 10% solution of Prepodyne (West 

Chemical Products Ltd.). During operation, the system 

is isolated from surface water, and workers involved 

with fish ponds are required to disinfect boots and 

equipment used in and around the system. 

To maintain the &sease-free certification of our 

hatchery according to Canadian Fish Disease Regulations, we prolong the walleye hatching period to 21 d 

using cold 50°F (10°C) water. This allows sufficient 

time to test parental fish for the presence of various 

diseases (infectious hematopoietic necrosis, infectious 

pancreatic necrosis, ceratomyxosis, furunculosis, 

bacterial hdney &sease, enteric redmouth &sease, 

whirling disease, viral hemorrhagic septicemia, 

edwardsiellio si s, pseudomonad septicemia, vi brioisi s, 

motile aeromonad septicemia, and myxobacterial 

infections). Prior to placement in the incubation jars 

and after the eggs are fully hardened, they are &sinfected with a 10 min immersion in a 1 % solution of 

Prepodyne. During incubation, additional prophylactic 

treatments are not required. Dead eggs are removed 

daily. Water recycling is high during egg incubation, 

minimizing water use. 

We have also designed a system to exert control over 

the developmental age of larvae at the time of hatching. 

During the hatching period the larvae accumulate in a 

158.5 gal (600 L) holding tank after leaving the 

incubation jars. The outlet of the holdmg tank is 

provided with a removable screen. During hatching 

water velocity through the incubation jars is increased 

to help move larvae out of the jars and to flush lipids 

and other wastes from the jars and tank. Larvae remain 

in the holding tank 3-4 d and are moved to the rearing 

trough about 1 d prior to disappearance of the yolk. 

During this period, we siphon out empty egg shells and 

dead larvae once or twice a day. The cleaning process is 

simplified by manipulating light levels, which in turn 

controls the behavior of the larvae. Newly hatched 

larvae avoid dimly lit areas and are strongly attracted to 

the beam of an ordnary flashlight or desk lamp. 

Larvae are transferred from the holding tank by means 

of a small 0.005-in (125-p) mesh nylon net supported 

on two sides by wood dowels. In the absence of a fry 

counter, we estimate larval numbers volumetrically. 

Groups of 1,000-2,000 larvae are netted and most of 

the water drained from the net. The larvae are gently 

poured into a 50 ml graduated cylinder to which a 6 in 

(15 cm) diameter funnel is clamped. Prior to this, the 

number of larvae occupying 2-3 ml of a 10 ml graduated cylinder is determined by actual counts of several 

samples. Appropriate quantities of larvae are then 

placed in the trough, which was filled with water 

maintained at the same temperature as that of the 

holding tank. After the larvae are moved to the trough, 

the temperature in the trough is raised to 68°F (20°C) 

over the next 48 h. 

The system requires a maximum flow rate of about 

1,850 gaud (7 m3/d). Water temperature is maintained at 

68°F (20°C) during the 30-d culture period. We keep 

dissolved oxygen concentration close to the saturation 

level, or at least >65% of saturation. Unionized ammo188 NCRAC Culture Series 101- Walleye Culture Manual 
Intensive Culture of Walleye Fry - Chapter 7 

nia concentrations are held at <O. 1 ppm (c0.1 mg/L). 

Total ammonia concentrations do not exceed 0.7 ppm 

(0.7 mgk). We find these levels can be maintained at 

the larval and feed densities we use. Declining oxygen 

levels can be corrected by more diligent cleaning, 

backwashing of the filter, and flushing of sludge in the 

particle remover trap. 

During the period when the swimbladder is inflating we 

supply make-up (“fresh”) water at a rate of 1,664 gal/d 

(6.3 m3/d). This high level, which is equivalent to 2.5 

exchangedd, reduces the accumulation of surface oils 

and films which inhibit swimbladder inflation. During 

the remainder of the larval culture period this volume is 

reduced to 185 gal/d (0.7 m3/d) (equivalent to an 

exchange of the system every 2.5 d). 

We have had good success by supplying feed shortly 

before the larvae will accept it. We now think that the 

percentage of fish with inflated swimbladders can be 

significantly improved by withholding food until the 

level of swimbladder inflation reaches 80%. Feeding 

attacks (attempted cannibalism) among larvae, the main 

cause of mortality at ths stage, are minimized by 

uniform lighting to avoid dense concentrations of larvae 

in brightly lit localities and precision feedmg to ensure 

an adequate density of food particles. 

We feed the larvae Fry Feed Kyowa (FFK) B-400 

(Biokyowa Inc., Chesterfield, MO) feed for the first 7 d 

and FFK C-700 feed thereafter up to 30 d. If necessary, 

larvae are fed B-400 feed longer to ensure that all 

individuals are ready for the larger C-700 feed. This 

feeding strategy gives smaller fish a chance to catch up 

in size to larger ones and may, to some extent, retard the 

growth of larger ones, so that variation in size will be 

minimized. The automatic feeders we use are custom 

built and are capable of reliably releasing about 0.002 

oz (0.06 g) of B-400 food per delivery. We have been 

unable to obtain precise control of feed delivery using 

commercial vibratory feeders. We have used five of the 

custom built feeders per trough, but thnk ten would 

ensure a more even feed distribution. If ten feeders were 

used, each would need to deliver feed at about 2 min 

intervals to maintain the correct feed particle density in 

the water. The larvae are held under continuous 

illumination and fed on a 24 h cycle. We think that 

continuous light reduces the incidence of cannibalism 

which would result from food deprivation during hours 

of darkness if a 1ight:dark rhythm was used. 

Feed is supplied in quantities sufficient to maintain a 

density of at least 378 particledgal (100 particlesL). 

We monitor feed particle density and adjust the output 

of the feeders to maintain the desired feed density. The 

same procedure is used after the diet is changed to C700. Overall total quantity of B-400 used in a single 

rearing unit has averaged 12 lb (5.4 kg) over a 7 d 

period. The average total amount of C-700 has been 

30.2 lb (13.7 kg) for the remaining 21 d. It is important 

to note that we do not base the feeding rate on the 

number of fish present, or the density of fish, but rather 

on maintaining in suspension about 378 particledgal 

(100 particlesL). 

A major objective of our research has been to reduce 

the labor requirements which constitute a substantial 

portion of aquaculture production costs. A system has 

been developed which minimizes labor costs. The 

system described above, requires 5 h of labodd to 

produce the numbers of 30 d juveniles described below. 

At times the labor has to be dispersed over 24 h to 

monitor the larvae. 

Much of the labor involves tank cleaning. The system 

relies on supplying an excess of food, which must later 

be siphoned from the trough once or twice daily. The 

outlet screens must be removed and cleaned once or 

twice daily, using a high-pressure water hose and longhandled brush. Every second day, after the fish are 

receiving C-700, the trough sides and bottom must be 

brushed or wiped as needed to remove the organic 

residue which accumulates on the trough surface (we 

use solid kitchen scrub pads). Sludge traps in the 

particle remover and elsewhere in the system need to be 

drained every 2-3 d. 

Other tasks involve monitoring water quality parameters, swimbladder inflation, feed supply and particle 

density, level of feeding, growth rate, general wellbeing of the larvae, and level of cannibalism. The latter 

is determined if a fish is observed grasping another tailfirst in its mouth. This lund of cannibalism is indicative 

of a much more prevalent form in which the victim is 

grabbed from the side, held for a few seconds and 

released after a struggle. Almost all fish held this way 

eventually die. These brief attacks outnumber the tailfirst form by a factor of 9: 1, hence evidence of even a 

few larvae being swallowed tail-first indicates that far 

more are being lulled by brief side attacks. 

NCRAC Culture Series 101 - Walleye Culture Manual 189 
Chapter 7 - Intensive Culture of Walleye Fry 

The system described has produced 23,000 30-d-old 

juveniles from a starting density of 72 larvae/gal(l9 

larvaek). An initial density of 21 1 larvae/gal (56 

larvaek) produced 33,500 juveniles. Survival to 30 d 

was 47% and 23% respectively. Swimbladder inflation 

at 72 larvae/gal(l9 1arvaeL) was 16% and at 211 

larvae/gal(56 1arvaeL) was 23%. The primary goal of 

our most recent research has been to restore successful 

swimbladder inflation to the level of over 80%, which 

occurred when the fish were raised in smaller 41 gal 

(1 54 L) tanks. Changes in culture procedure, by 

culturing identically-aged larvae and delaying feeding 

until swimbladder inflation is almost complete seems to 

result in 80% swimbladder inflation. 

190 NCRAC Culture Series 101- Walleye Culture Manual 
Colesante, R. T. 1996. Intensive culture of walleye using brine shrimp and formulated diets. Pages 

191-194 in R. C. Summerfelt, editor. Walleye culture manual. NCRAC Culture Series 101. North 

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

Intensive Culture of Walleye Using Brine 

Shrimp and Formulated Diets 

Richard T: Colesante, New York State Department of Environmental Conservation, Oneida Fish Cultural 

Station, Constantia, New York 13044 

Introduction 

Fisheries management programs in New York State 

annually require 300,000 advanced (4-6 in, 10.2-15.2 

cm) fingerling walleyes. To fulfill management’s 

request, a fish culture research project was established 

to develop methods to produce fingerlings efficiently. 

Over a 12 year period, this research evolved into an 

intensive culture protocol using brine shrimp and 

formulated dets. This case study describes the methods 

used by the New York State Department of Environmental Conservation (NYSDEC) to intensively culture 

advanced walleye fingerlings at the new Oneida Fish 

Cultural Station. 

Oneida Lake Fish Cultural Station 

The new hatchery was completed in 1993. It is a single 

story building about 240 x 80 ft (73.2 x 24.4 m). Two 

thirds of this building is devoted to fish production with 

space for tanks, egg incubation, and brine shrimp 

production. The remaining portion of the building is 

devoted to water treatment includmg filtration, ultraviolet sterilization, oxygen injection, water heating, and 

fish culture research. The water used in the hatchery is 

from Scriba Creek, a soft-water (35 ppm calcium 

carbonate) tannin-colored stream. Water from Scriba 

Creek is impounded behnd a concrete dam 0.3 mi (0.48 

km) above the hatchery; water flows from the dam to 

the production facility by gravity. There is about 8 ft 

(2.4 m) of head in the production portion of the 

building; maximum flow of water is 1800 gpm (1 13 L/ 

sec). 

The Oneida Fish Cultural Station has 32 fiberglass 

rectangular tanks with charcoal-colored (gel-coated) 

sides and aqua blue bottoms. These tanks are 25 x 4 x 

2.3 ft (7.6 x 1.2 x 0.7 m) (length x width x depth); water 

levels can be adjusted by changing the height of stand 

pipes, and volume will vary from 150 ft3 (4.2 m3) when 

fry are stocked to 180 ft3 (5.1 m3> when fingerlings are 

trained to accept formulated diets. Twenty-three tanks 

are used to start walleye fry on brine shrimp. Each of 

these designated start tanks is equipped with a 15 gal 

(56.8 L) capacity liquid (brine shrimp) feeder supplied 

with air for aeration of the brine shrimp slurry, and a 

0.625 in (1.6 cm) solenoid valve which is normally 

closed. A 22-ft long (6.7-m) fiberglass feeding tube 

with 0.125 in (0.3 cm) holes drilled at 6 in (15.2 cm) 

intervals is used to dnpense nauplii along the length of 

the tank. This feedmg tube has an independent water 

source, supplying up to 2 gpm (7.6 Lpm) to flush the 

tube and nauplii into the tank. The feeding tube is 

adjusted to about 6 in (1 5.2 cm) above the surface of 

the water. Two Loudon-type feeders are used for 

dispensing formulated let. These feeders cover 18 ft 

(5.5 m) of the 23 ft (7.0 m) of usable space in each tank. 

A set of high-intensity lights can increase light intensity 

to 680 lux at the water’s surface; ambient hatchery 

lighting produces 140 lux at the surface. The other nine 

tanks at the hatchery are equipped with Loudon-type 

feeders only and are used after fingerlings are trained to 

accept formulated diets. 

A 50-mesh stainless steel screen is initially used to 

confine walleye fry and brine shrimp in each tank. A 

38-mesh screen is sometimes used on or about day 15; 

however the 50-mesh screen is often left in place until 

30 d. At this point, a slotted 3/64 in wide x 0.5 in long 

(0.1 x 1.3 cm) aluminum panel is used to facilitate 

increased flows. After fish are trained to accept a 

pelleted ration, a 0.125 x 0.75 in (0.3 x 1.9 cm) slotted 

panel is used until fall when fish are harvested for 

stochng . 

Brine shrimp production 

The production of brine shrimp nauplii at the Oneida 

Fish Cultural Station is accomplished using 15,70 gal 

(265 L) cylindncal, insulated tubs which are 24 in 

diameter x 43.5 in height (61 x 110.5 cm). Each unit is 

NCRAC Culture Series 101 - Walleye Culture Manual 191 
Chapter 7 - Intensive Culture of Walleye Fry 

equipped with an aeration ring made of 0.5 in (1.3 cm) 

PVC with 0.125 in (0.3 cm) holes, a 300 w submersible 

aquarium heater, a clear plexiglass cover, and a remote 

25 w light source. Aeration is provided by two highvolume, low-pressure air pumps. Heated and unheated 

cultural water is supplied to the brine shrimp area. 

Water is manually adjusted to 80-85°F (27-29°C); thus 

temperature is maintained by the submersible heater. 

Salinity is adjusted to 18 ppt by adding non-iodized 

granulated salt. After loading up to 5.5 g/L of cysts into 

tubs, the brine shmp solution is strongly aerated for a 

24 hr incubation period. 

To harvest the nauplii, the aeration, light and heat are 

turned off. The slurry is allowed to stand for 5-10 min 

so the outer shell of the cysts, unhatched cysts and 

nauplii separate in the water column. A valve is then 

opened that draws fluid from the bottom. The first 

gallon that contains unhatched cysts is discarded; the 

remaining fluid contains a nauplii suspension and is 

saved, except the contents at the very end of the vessel. 

The nauplii slurry is placed in the feeders. 

Fry culture 

Gametes from wild Oneida Lake broodstock are 

generally collected in April. Prior to hatching, a portion 

of the fertilized eggs are designated for fingerling 

production using the intensive culture techniques. These 

eggs are placed on a separate egg incubation battery and 

allowed to hatch for 24 h. Fry hatched during this 

period are collected in a holding trough; eggs unhatched 

at the end of this period are removed from the egg 

battery. In this manner, only fry of known age (between 

0-24 h) are used in the culture program. 

Walleye fry from different genetic strains initiate 

feeding at different times. Oneida Lake walleye fry 

begin to feed around 100°F (37.8”C) temperature units 

(TU). A temperature unit is defined as the average daily 

water temperature (Fahrenheit) minus 32°F; therefore at 

an average water temperature of 62°F (17”C), about 

30°F TU’s (16.6”C TU’s) are accumulated each day and 

walleye will initiate feeding between 3-4 d. 

About 90,000 (21.4 fry/L) known age walleye fry are 

stocked into start tanks 24 hrs prior to first feeding. Fry 

are inventoried by volumetric displacement; displacement values (fry/ml) are determined by sampling and 

counting of fry on the same day fry are stocked. 

Dependmg on their age, 160-210 walleye fry will 

displace one ml of water. 

Water flow in each of the 23 start tanks is set between 

10-15 gpm (37.8-56.8 Lpm) to minimize any effect of 

flow on fry &stribution in the tank. A minimal water 

temperature of 55°F (12.8”C) is needed to start fry on 

brine shrimp. At Oneida, because ambient creek 

temperature can fluctuate 3-5°F (1.7-223°C) in a 24 hr 

period, water is usually heated to 5840°F (14.4- 

15.6”C). Propane-fired boilers, heater exchangers, and 

packed columns are used in the heating process. When 

ambient Scriba Creek temperature remains above 55°F 

(12.8”C), water is not heated. 

High-intensity lights, over each start tank, produce 680 

lux at the water’s surface. These lights are activated 

when fry are stocked. The increased light intensity aids 

in achieving even linear distribution of fry throughout 

the tank; since walleye are cannibalistic, dispersal of 

individuals is important. It also attracts fry to the 

surface of the tank which may aid in the process of 

swim bladder inflation. 

Darkened sides on the rearing tanks minimizes “sideclinging behavior’’ of newly hatched walleye fry. If 

uncontrolled, this activity can result in lower swim 

bladder inflation and feeding rates. 

First feeding with brine shrimp 

Nauplii production starts 24 h before walleyes are 

scheduled to receive their first food. Initially, a feeding 

rate of 800-1 000 nauplii/fish/day is targeted. This 

requires incubating about 2.2 Ib (999 g) of cysts in each 

of five tubs at 0800 h and the same quantity of cysts at 

1800 hours. 

The brine shrimp nauplii are harvested 24 h later from 5 

tubs in the morning and 5 tubs in the evening. The 

hatched nauplii slurry, roughly 300-325 gal (1 135- 

1230 L) from 5 tubs, is loaded directly into brine 

shrimp feeders following each harvest. 

All brine shrimp nauplii put into a feeder during a 24 h 

period are used during that 24 h period. Usually, feeders 

dispense nauplii every 8 min for a 3-sec interval 24 h/d. 

Upon activation, the feeder dispenses a 500-600 ml 

slurry of brine shrimp into the feedmg tube. The nauplii 

192 NCRAC Culture Series 101- Walleye Culture Manual 
Intensive Culture of Walleye Fry - Chapter 7 

are flushed from the feeding tube at 6 in (15.2 cm) 

intervals along the length of the tank. 

Swim bladder inflation in Oneida Lake walleyes is 

initiated around 160°F temperature units (71.1 “C TU’S) 

(8-10 d). Usually within 2 d of ths point, flow in each 

start tank is increased to between 20-25 gpm (75.6- 

94.6 Lpm). Over 90% of the fish raised at the Oneida 

Fish Cultural Station initiate feeding and inflate their 

swim bladder. Sampling to determine swim bladder 

inflation and feeding rates is not done anymore, and 

problems in these areas are not anticipated. 

High-intensity lighting, darkened tanks sides, adequate 

prey density, and water quality (i.e., color and hardness) 

are probably responsible for this success. 

In this system, mortality and cannibalism between day 

0 and the initiation of swim bladder inflation is insignificant. However, when air is first detected in the swim 

bladder (8-10 d), mortality increases. The mortality is 

generally caused by a pectoral fin nip (attack) by 

another fish that results in death either immediate or 

slightly delayed. Uncontrolled nipping behavior can kill 

as much as 25% of the fish in a 24 hr period. Mortality 

from this source can be managed by reducing light 

intensity from 680 lux to 140 lux at the water’s surface 

by turning “OW’ high intensity lights above the start 

tanks. This action allows the fry to disperse vertically 

and occupy the entire 18 in (45.7 cm) water column, 

instead of the upper 6 in (15.2 cm). This effectively 

reduces fry density by up to two-thuds and minimizes 

losses during this period of hgh mortality. 

Diet training period 

On day 30, brine shrimp feeding is increased to 1,300 

nauplii/fish/d, based on the original number of fish, 

without consideration of mortality. At this point, 3 lb 

(1.4 kg) of cysts are incubated in each tub, which is a 

total of 30 lb (13.6 kg) of cysts per day. Also on day 30, 

water flow in each tank is increased to 35 gpm (1 32 

Lpm) and feeding of formulated diets is started. The 

feed used at the fish cultural station is called the “New 

York State diet”. It is a high quality (48% protein, 18% 

fat, 10% moisture, 8% ash) open formula feed (Table 

1). Limited amounts (a 50:50 mixture of starter and 1 

crumbles) are fed at 5 min intervals through 44 d, along 

with brine shrimp. 

After two weeks of mixed feeding (d 44 posthatch), the 

feeding of brine shrimp nauplii is stopped and walleyes 

Table 1. Ingredients used in NewYork 

State diet, No. 1. 

Ingredient Percent 

He r r i ng -f is h meal 

Dried whey 

Dried blood flour 

Corn gluten meal 

Dried brewers’ yeast 

Condensed fish solubles 

Soybean lecithin 

Tuna or herring oil 

Vitamin pre-mix 

Extruded wheat 

Vitamin pre-mix No. 2 

Choline chloride 

Lignin sulphonate pellet binder 

Trace mineral mix 

Calcium propionate 

Ascorbic acid as Stay-C 

58.0 

8.0 

5.0 

5.0 

3.0 

2.5 

1 .o 

12.0 

3.0 

remainder 

3.0 

0.58 

2.0 

1.5 Ib/ton 

2.5 Ib/ton 

225 ppm 

are only fed no.1 crumbles of the New York diet. 

Feeding levels of formulated feed are increased to 15% 

of body weight. The diet training period will generally 

last 2-3 weeks (44-65 d), depending upon water 

temperature. Fish quickly separate into two groups, 

those which accept the feed and those which do not 

(dark, listless fish). High temperatures accelerate this 

separation. If non-feeding fish are moved to a separate 

tank, significant numbers of these fish will feed. This 

technique is used to increase survival and to take 

advantage of easy removal (grading) of smaller nonfeeding fingerlings. 

Survival during the diet training period is affected by 

diet. Controlled experiments are conducted each year to 

evaluate formulated feeds; survival during the training 

period can range from 10-70% dependmg on the feed. 

Our present diet generally produces a 50% survival of 

fingerlings during the diet training period. In 1994, a 

new diet produced by Rick Barrows (of the United 

States Fish and Wildlife Service, Bozeman Technology 

Center, Bozeman, Montana) produced 70% survival 

during this period. 

Disease outbreaks can affect survival during the diet 

training period. Fish being trained to accept formulated 

NCRAC Culture Series 101 - Walleye Culture Manual 193 
Chapter 7 - Intensive Culture of Walleye Fry 

Begin brine shrimp feeding (d 3) - 2000 - t 

- 

- 

v + 

L 

800- 

E - 3 400- \End training to formulated diets (d 65) - *-----+ 

0 I I 1111 

0 20 40 60 80 100 120 140 160 

Age (d) 

*Brine shrimp feeding was extended 8 d in 1993. 

Figure 1. Survival of walleye during the 1993 production 

season. 

diets are under considerable stress and predisposed to 

hsease. Constant observation and prompt treatment of 

pathogens can be critical to success. 

After being trained to formulated diets (65 d), water 

flow in each tank is set at 45 gpm (2.8 Wsec) to produce 

2.5 exchanges of waterhr, and requirements for care 

and maintenance of walleye decreases. Growth after 

fish are trained to consume formulated diets (66-150 d) 

is rapid (Figure 1) and culture densities up to 2.5 lb/ft3 

(40.1 kg/m3) are commonly achieved with no ill effect. 

Survival during ths period following training has 

ranged from 6545% during the 2 years of production 

in the new hatchery. 

Fish continue to be fed during this period at 5 min 

intervals, 24 hr/d under constant light (140 lux). 

Feedmg rates are adjusted on a weekly basis to accommodate rapid growth; generally fish are fed at 10% of 

total body weight. Particle size of the New York State 

diet is increased as the fish grow; usually particles no 

larger than a 4 crumble are fed to fish stocked as fall 

fingerlings, 4-6 in (1 0.2-1 5.2 cm). The feed conversion 

averages 2.4 and ranges from a high of 5 in May 

(during &et training) to a low of 1.6 in August when 

fish are feeding on formulated diets. 

Inventory of walleye after fish have been trained to 

accept a pelleted ration is generally done by sampling 

to determine the number of fish per pound and then 

weighng or displacing all fish. Walleye tolerate this 

type of handling very well. Most fall fingerling walleye 

are stocked in New York between September 15-30. 

Walleye appear to go on a maintenance (no growth) diet 

when water temperatures drop below 60°F (1 55°C). 

Summary 

Production of walleye fingerlings using economical 

and efficient methods are goals of the New York State 

walleye culture program. Survival of walleye during the 

I993 production season, the first year of production 

incorporating “new” culture techniques are encouraging 

(Figure 2). One hundred ninety thousand fingerlings 

between 4.3-5.2 in (10.9-13.2 cm), 2441/lb (10.9- 

18.6/kg), were stocked; about 30,000 fish less than 

production goals. Overall survival for the entire 1993 

production season (0-150 d) was 13.7%. 

Projected walleye survival established through research 

and development was 57% to 30d, 50% from 31 to 65 

d, and 50% from 66 to 120 d posthatch. Actual survival 

was 42% to 30d, 33% from 31 to 65 d, and 65% from 

66 to I20d posthatch. Differences between projected 

and actual survival during day 0-65 are related to a 

NYSDEC moratorium on the use of unapproved 

chemicals in treating dseases of fish. As a result, 

diseases previously treated with chemicals are now 

allowed to run their course. It is expected that survival 

(0-65 d) will improve to projected levels when disease 

epizootics can be adequately controlled. 

Overall, the intensive culture program for walleye 

fingerlings has met and exceeded expectations. Survival 

of fingerlings after being trained to formulated diets has 

been excellent; the growth of fingerlings to fall stocking 

has been much greater than expected. Each year of 

production has resulted in improvements in operational 

efficiency and also the future outlook for the intensive 

culture of walleye. 

*O 1 , 

- 80 

- 60 

- 40 

- 20 

I’ll1 Io 

0 20 40 60 80 100 120 140 160 

Age (d) 

Figure 2. Growth of walleye during the 1993 

production season. 

194 NCRAC Culture Series 101- Walleye Culture Manual 
Moore, A. A. 1996. Intensive culture of walleye fry on formulated feed. Pages 195-1 97 in R. C. 

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

Aquaculture Center Publications Office, lowa State University, Ames. 

Intensive Culture of Walleye Fry on 

Formulated Feed 

Alan A. Moore, lowa Department of Natural Resources, RR 2, Moravia, lowa 52571 

Introduction 

Many resource management agencies are planning to 

produce substantially more large 6-8-in (15.2-20.3 cm) 

fingerling walleye for fisheries enhancement stocking 

compared with traditionally stocking of fry or small 

fingerlings. Currently, large fingerlings are produced in 

large winterkill lakes (Kinnunen 1996), and by tandem 

pond-tank culture methods (Held and Malison 1996). 

The latter production method include stoclung fry in 

ponds, raising them to 2-in (5 cm), then training these 

fingerlings in tanks to accept formulated feed. Because 

of mortalities that occur in both pond culture and during 

the intensive culture phase, raising walleye from fry to 

fingerling on formulated feed is an attractive alternative. 

The two main problems of poor gas bladder inflation 

and low survival have slowed acceptance of this 

technique, however, these problems have been solved 

with the use of a surface spray to increase gas bladder 

inflation, and the Fry Feed Kyowa (FFK) B-400 to B700 feeds (BioKyowa Inc., Chesterfield, MO) (Moore 

et al. 1994a, 1994b). Currently at the Rathbun Hatchery, 

20,000-35,000 6- to 7-in (15.2-17.8 cm) fingerlings are 

produced solely on formulated feed in intensive culture 

environment. The objective of this paper is to summarize the walleye fry feedmg techniques used at Rathbun. 

Methods 

Tank setup 

Two sizes of cylindrical tanks 73.4 and 179.3 gal (278- 

L and 679-L) have been used for fry walleye feeding 

(Figure 1). Each has a center drain and a water inflow 

pipe located vertically along the tank side. The inflow 

pipe has 1/16-in (1.6-mm) holes drilled approximately 

13/32-in (1 O-mm) apart on the lower 12.2-in (3 1 -cm) of 

the pipe. The flow is directed in a clockwise direction 

and is 0.8 gaUmin (3.0 L/min) for the first day after 

stocking, and increased to 1.5 gaUmin (5.7 Wmin) 

thereafter. To clear the surface of oil and feed to 

enhance gas bladder inflation, the tanks are equipped 

with one to four surface sprays. A single surface spray 

of about 0.4 L/min is located mid-way between the tank 

wall and center screen of the small tanks; the large 

tanks have four sprayers. The tank area is covered with 

a black plastic curtain for the first two weeks of feeding 

and an incandescent light at 100 to 200 lux is recommended. The lighting helps to distribute fry evenly 

throughout the tank and to reduce fry congregation at 

the tank sides. To aid in fry dispersal, the tank sides are 

black, or shaded, and the bottom is a lighter color to aid 

in cleaning. Tanks are illuminated approximately 

24 h/d. 

Fry stocking and feeding 

Walleye fry, approximately 1 -3-d of age, are stocked at 

1,132/ft3 (40 fry&) (1 1,120/small tank and 27,16O/large 

tank). We enumerate fry for stocking using a mechanical counter (Model FC2, Jensorter Inc., Bend, Oregon), 

however, the volumetric method of enumeration, in 

which fry are allowed to settle in a graduated cylinder, 

may also be used. Sample counts to determine the 

number of fry/ml must be performed prior to using the 

volumetric method. Fry begin feedmg when they are 

four to six days old, or as soon as mouth parts are 

developed. Feed amount and particle size is based on 

fish length and is dispensed as grams of food/l,O00 

fry/d (Table 1). Fry are fed FFKl3-400 or B-700,20-22 

h a day, seven d/week. Feed is dxpensed at 5-min 

intervals using an auger type feeder and an automatic 

timer to activate the feeders. One feeder is located on 

the small tanks and two feeders on each large tank. 

Food acceptance and fry survival is greater at 65°F 

(18.4"C) than at 55°F (12.8"C). The ideal temperature 

range is 60-65°F (15.6-18.4"C) with 65°F (18.4"C) 

being optimum. To stimulate feeding, which increases 

fry survival and reduces cannibalism, a 9°F (5°C) 

temperature boost for 24 hours, 5 days posthatch is 

recommended. The temperature is then lowered to the 

original setting. 

NCRAC Culture Series 101 - Walleye Culture Manual 195 
Chapter 7 - Intensive Culture of Walleye Fry 

Tank Cleaning and Disease rn 1 anks are cleaned with a siphon on a 

daily basis to remove waste feed and 

dead fry. Screens are removed and 

sprayed until clean and the tank 

surfaces are wiped with a sponge 

beginning on day six. 

Bacterial gill disease is the only 

disease problem that has been 

encountered during the first 25 days 

of feedmg. A chloramine T treatment 

of 5.0-10.0 mg/L for 1 h for two 

consecutive days usually is effective 

with no adverse effect on the fry. An 

Investigational New Animal Drug 

permit from the Food and Drug 

Administration is required before the 

Chloramine T can be legally used. 

However, bacterial gill disease starts 

Table 1. Feeding regime (FFKB-400 and 6-700) by length 

of walleye. The ratio of feed type and feed amount is 

changed when fry exceed the corresponding length. 

Fry length Ratio of feed type 

(mm) Grams food/l,OOO fish (B-400: B-700) 

<11 

11-13 

13-1 5 

15-1 7 

17-1 9 

19-21 

21 -23 

3.0 1oo:o 

5.8 75:25 

7.3 50:50 

8.5 25: 75 

10.1 0:lOO 

Ratio of B-700:WG92061 

11.9 75:25 

13.6 50:50 

WG9206 is an open formula diet formulation by F.T. Barrows, US Fish and Wildlife 

Service Fish Technology Center, Bozeman, MT, and manufactured by Sterling H. 

Nelson and Sons Inc., Murray, UT. 

and is not controlled, substantial mortalities may occur. 

Fry survival-large fingerling production 

Fry survival at day 25 posthatch has ranged from 35 to 

75% using the methods described. The highest survival 

occurred at a water temperature of 65°F (1 8.4"C) and 

turbidities of 15-30 NTU. Turbidity seems to allow for 

better fry dispersal in the tank and better food acceptance and gas bladder inflation (Bristow and Summerfelt 1995). At Rathbun, fry length ranged from 0.75-0.9- 

in (19-23-mm) and gas bladder inflation was >90% at 

25 days posthatch. Walleye are moved to raceways for 

final grow-out after 25-30 d. When water temperatures 

range from 75-78°F (23.9-25.6"C) walleye fingerlings 

will grow 0.5 idweek (12.7-mm), and they will reach 

6.5-7.5 in (16.5-19.0-cm) at 150 d posthatch. 

Ref e re n ces 

Bristow, B.T., and R.C. Summerfelt. 1994. Performance 

of larval walleye cultured intensively in clear and 

turbid water. World Aquaculture Society 25:454-464. 

Kinnunen, R.E. 1996. Walleye fingerling culture in 

undrainable ponds. Pages 135-1 45 in R.C. Summerfelt, editor. Walleye Culture Manual. NCRAC Culture 

Series 101. North Central Regional Aquaculture 

Center Publications Office, Iowa State University, 

Ames . 

Malison, J.A., and J.A. Held. 1996. Habituating pondreared fingerlings to formulated feed. Pages 199-204 

in R.C. Summerfelt, editor. Walleye Culture Manual. 

NCRAC Culture Series 101. North Central Regional 

Aquaculture Center Publications Office, Iowa State 

University, Ames . 

Moore, A., M.A. Prange, R.C. Summerfelt, and R.P. 

Bushman. 1994a. Evaluation of tank shape and a 

surface spray for intensive culture of larval walleyes 

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. Progressive Fish-Culturist 56: 194-201. 

196 NCRAC Culture Series 101- Walleye Culture Manual 
Intensive Culture of Walleye Fry - Chapter 7 

a inflow 

b feeder 

c spray 

d screen 

e drain 

a 

Figure 1. Top and side views of a small tank (278-L, right) and a large tank (676-L, left) used 

for walleye fry culture. Vertical inflow pipes (a) have been drawn next to the tanks to show 

inflow openings in lower third of pipe. Current direction (clockwise) is shown by arrows. 

(From Moore et al. 1994). 

NCRAC Culture Series 101 - Walleye Culture Manual 197 
Chapter 7 - Intensive Culture of Walleye Fry 

198 NCRAC Culture Series 101- Walleye Culture Manual