Apr
               MAY
				Jun11
				Next capture2008
               2009
				2010**2 captures**
           8 May 09 - 11 May 09
   Close
       Help


Ashland NFWCO
 Midwest Region
 Dedicated To The Tribal Aquaculture ProgramImage of fish jumping.
    September
        2002-Volume 41

**Administrative
        Coordinator:
        Frank G. Stone 
        (715-682-6185) Ext.
        202
        U.S. Fish and
        Wildlife Service
        Email: 
        [email protected]**
      **Edited
        By:
        Elizabeth W. Greiff 
        (715-349-2195) Ext. 141
        St. Croix Tribal Nat. Res. Depart.
        Email:**
      **[email protected]** Topics
Of Interest: Intensive
Culture of Walleye Fry Introduction
      Clinging Behavior
      Light and temperatureAdvantages of Intensive
        Culture
      Nonfeeding
      Turbid water cultureProlarval Stage
      Cannibalism
      Stocking densityPostlarva I
      Basic methodology
      Feeds, feeders and feedingPostlarva II
      Culture tanks
      Tank hygieneJuvenile
      Screens
      Water flowCritically important
        cultural problems
      Surface spray
      Water qualityNoninflation of the
        gas bladder (NGB)
      Aeration and pumping
      Case studies
 Lets Get Tanked  The following information
was obtained from the Walleye Culture Manual (NCRAC).
What follows is a slightly shortened version of the actual article. If you need
additional information or the list of references, please refer to the manual or
contact Dr. Summerfelt.  Intensive
Culture of Walleye Fry By: Robert C. Summerfelt, Department of Animal Ecology, Iowa State
University, Ames, IA.   Introduction Walleye may be raised from newly hatched fry to phase I fingerlings in
extensive or in intensive culture, that is in tanks and raceways. Currently, the
predominant method for raising phase I fingerlings is in drainable or
undrainable ponds. 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.  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. 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 II
fingerlings ( 6 inches), or for the commercial grow out from fry to food fish.
Pond culture of phase II fingerlings requires relatively low initial pond
stocking densities, or partial harvest and restocking, followed by provision of
substantial quantities of minnows. 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. 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. In extensive-intensive culture, substantial mortality typically
occurs at two intervals. First in the pond, and secondly in the intensive
culture system during the first 21 days when fish are habituated to formulated
feed. 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 lacking,
cannibalism may occur in the pond. 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 days 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 conditions, 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 intensive culture system than in pond culture. In spite of high
stocking density, cannibalism may be less of a problem in intensive culture than
pond culture because it 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. 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 II fingerling to a
target size of 6 to 8 in by fall in either ponds or cages. Would intensive fry culture with heated water be economical for commercial
producers? As a rule, heating water for production aquaculture is uneconomical.
The larger operators typically have a source of steam or warm water from
coal-fueled electric generating plants or facilities that distill alcohol. Prolarval Stage The prolarval stage is also called a free embryo or eleutheroembryo, 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. At a mean temperature of 16.4
C, the yolk sac disappears in the 5th day posthatch, about 68 temperature units
(TU), but it may
persist up to about 13 days at a temperature of 13.2C. 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 vehicle,
the larvae pile up and suffocate. Hatchery personnel frequently measure the volume of a known number of 2-3
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. 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 stocking, about 2-3 days
posthatch. Postlarva I Postlarva I is the stage following absorption of the yolk sac but before
disappearance of the oil globule. After disappearance of the yolk, or slightly
before then, larvae begin feeding (exogenous feeding), and gas bladder inflation
begins. Krise and Meade (1986) indicated that first feeding begins at 100-122
TU. Our measurements indicate that the TU to yolk sac disappearance (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, which is sufficiently large to cannibalize
similar-sized siblings or to consume the standard size 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
feeding 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 II. Postlarva II Postlarva II begins about the time the oil globule disappears, which is about
226 TU, in the 14th day posthatch at a mean temperature of 61.5F (16.4C). 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
exhibit a stress syndrome behavior, or they revert to prolarval behavior,
swimming to the surface and drifting back to the bottom. These behavioral
patterns may be related to noninflation of the gas bladder. The end of the postlarval II 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. The end of
postlarval II stage and beginning of the juvenile (fingerling) stage is not
marked by conspicuous and convenient developmental milestones. The swim bladder
has inflated and fish are feeding successfully or the fish dies. 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. Juvenile Juvenile stage begins about 15-18 days posthatch at a length of about 20 mm.
At the end of the postlarval II 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. Scale development begins at 24 mm but it is not
completed until they are 45 mm. 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 until gas bladder inflation is first detected (8-10 days posthatch)
as a means to attract fry to the surface for gas bladder inflation. After gas
bladder inflation begins, reduce light intensity to 140 lux for the duration of
the culture interval to disperse 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. 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 or intank
lighting is used 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. Nonfeeding 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 nonfeeding 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), susceptibility to stress-induced mortality,
diseases and toxicant, it slows growth, and increases susceptibility to
cannibalism or predation. Fry without an inflated gas bladder struggle to
maintain position and they eventually starve because of the high energy cost of
swimming and difficulty in capturing food. NGB makes fry vulnerable to
cannibalism because fry without an inflated gas bladder have erratic behavior
and poor swimming ability. It was essential to develop effective strategies to
overcome this imposing problem. In most fish, initial filling of the gas bladder is accomplished
by gulping and swallowing air, then mechanically forcing air bubbles from the
foregut through the lumen of the pneumatic duct to the gas bladder. For walleye,
the interval of gas bladder inflation after hatch is said to be 214 TU. The
window of opportunity for initial gas bladder inflation is relatively short. It
is assumed that failure of the gas bladder to inflate during this specific
period of development is irreversible. 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 is ingested, but bubbles must be
small enough for passage through the pneumatic duct. The relatively large
bubbles ingested at the surface are fragmented by surfactant-like secretions in
the foregut. Immediately following initiation of gas bladder inflation, the
second stage begins when the vascular rate 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
elongated-shape. 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. 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 surrounding the air bubble. Although gas
bladder inflation advances to the spherical stage, 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. 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 lacking 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,
walleye are quite transparent and the gas bladder easy to observe. Fry are
observed in a petri dish on a dissecting microscope, using transmitted light
with 6-7 x magnification. Clinging behavior In intensive culture of walleye in relatively clear water, 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. Turbid water does an exceptional job of dispersing the fry. In
tanks with turbid water, fry are concentrated near the surface, but dispersed
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. Nonfeeding Early reports of nonfeeding by larval walleye raised in
intensive culture were commonplace: Nonfeeding fish and cannibalism were
considered the major problems for intensive culture of walleye. The problem was
related to color or palatability of the feed, or inadequate particle density,
but success with brine shrimp was sometimes poor also. Fry distribution within
the rearing tank may also affect the opportunity of fry to encounter and consume
feed particles. It seems that water turbidity improved the ability of larval
walleye to distinguish and eat. Perhaps it enhances contrast between the
brownish-orange feed and the milky gray color of the turbid water, or because
the light-scattering 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. 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. 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.
Most mortality from cohort cannibalism occurs from trunk attacks, not the result
of successful consumption of the prey, which is from the tail first. Cannibalism
begins as soon as the fry begin feeding and it can be a major factor in total
mortality when fish are not feeding. Cannibalism in intensive culture of
  walleye to 21-days posthatch differs among stocks. Thus, certain wild stocks
  that exhibit an inherent tendency to cannibalize should be avoided. 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. It has long been known that fish-size differential
  in walleye populations increases cannibalism. 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. Cannibalism is reduced in
turbid water culture, perhaps because fish accept formulated feed sooner than in
clear water. 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, Aeration and pumping, Light and temperature, Turbid water culture,
Stocking, Feeds, feeders and feeding, Tank hygiene, Water quantity and quality. Culture tanks 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, direct or reflected light. They will cling to the sidewalls, screens, and
they are even attracted to the bottom 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. Tank size is another
factor affecting clinging. A greater percentage of the stock cling to the sides
of smaller than larger tanks. Colesante (1996) reports that darkened sides of the rearing
tanks minimizes clinging behavior, and high-intensity lights help achieve
uniform distribution of fry, and attracts the fry to the surface to aid in the
process of gas bladder inflation. Corazza and Nickumn (1981) 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 until turbid water was used. Artificial
turbidity was developed by addition of a small volume of a clay slurry. Some
hatcheries have naturally turbid water (15-25 NTS) from colloidal clay that is
not removed by rapid sand filtration. With turbid water, clinging behavior
is avoided and tank color does not matter. 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. Since the 1990 culture season, the drain in our culture tanks
has been surrounded by 6-in PVC pipe which has large areas of PVC cut away, the
cut-away sections are covered with square-weave, monofilament nylon. 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 21days posthatch, 710Fm
mesh screens are used; after 21 days posthatch, a second set of screens with
1,000 Fm (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 Fm
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 Fm
mesh. Surface spray The spray (composed of tank water) removes the oil film and cleans the surface of feed
and debris. 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 (l994a) used
a flow rate of 0.3 to 0.5 L/min through the spray head and Bristow and Summerfelt (1994) 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. The sprayer is a 180 degree perimeter nozzle and it is directed at a
80~90 degree angle with the water surface from a distance of not more than 20 cm
above the water surface. The number of spray-heads needed has not been
critically evaluated. Aeration and pumping Degassing and aeration of the water supply should be done before
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 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 throw fry out of the water where
they will stick to the side walls above the water line. Barrows (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 screens are painted black, fry
attraction to reflected light will be reduced. 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. 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. Moore (1996)
reported that feed acceptance and survival is greater at 65 F than at 55 F, and
an ideal temperature range is 60-65 F, with 65 F as optimum. Turbid water culture Survival, length, and weight of larvae raised in turbid water to
21-30 days were significantly greater than for larvae raised in clear water.
Larvae were more evenly distributed in the turbid water than in clear water. The
turbid water was milky gray. In turbid water, larvae did not congregate on the
tank walls as they did in clear water. The light-scattering effect of turbidity
seems to reduce the amount of light reflected from the tank walls. The clinging
behavior of walleye to sidewalls was greatly reduced or eliminated in turbid
water.  When screens are painted black, fry attraction to reflected light will be
reduced. In turbid water, survival is increased, the fish are on feed sooner,
and their weight
at 21 to 30 d posthatch was 200 to 300% larger than weight of fry raised in
clear tanks. In all of the six comparisons of larval performance in clear and
turbid culture since 1993, the fish in turbid grew substantial faster than fish
in clear water. The system described by Bristow and Summerfelt (1994) to supply
a clay-slurry for six, 40 gallon tanks has been enlarged for use with six,
production-scale (264 gal) tanks. The clay slurry (8 g of clay per L) is stirred
with a commercial mixer with a 3 hp
motor that turns a shaft at 1,725 rpm. The clay slurry is distributed with a 2
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 require addition of clay
slurry every 20-minutes. 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. 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. Colesante and Schiavone (1980) attributed mortalities that occurred in
the first 36 hours 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 holding 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
stocking fry that were transported to our facility in plastic bags, but not with fry that were hatched on site from eggs that were shipped. 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. The counter can
count 500,000 fry per hour with an average error of 3%. Gravimetric methods were more accurate than volumetric estimates, which have
been the standard hatchery procedure. Recommendations for stocking density (number of fry/ L) for
large-scale production of walleye fry in intensive culture varies from 21 for
fry started on brine shrimp, to 40-56 for fry fed formulated feed. With
improvements in survival, stocking densities of 80 to l00/L 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 Early efforts in feeding formulated feeds quite naturally
included trout and salmon feeds, but all early efforts at feeding formulated
feed were unsuccessful. Feed size, color, and texture have been considered the
most important factors affecting acceptability. Failure of the fish to feed or
digest the feed has been cited frequently as a major factor in the failure of
walleye culture on formulated feeds.  There is no consensus 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 B-700 or C-700. 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 feeding small quantities of fry feed accurately
and consistently to prevent food deprivation or excessive feeding and tank
fouling. Feeding rates and feeding frequency are important for successful
fry culture. Feeding should be at 3-5 minute intervals at least 22 hours/day.
Feeding should be stopped only to clean the tanks. Survival has been poor when
feeding was stopped for more than an a 6 hour 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 cleaning of the sidewalls; 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 the 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. Water flow Before walleye fry begin feeding, 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 1.0 exchange by 21-days.
Higher flow rates are recommended by others. 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. 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 immediate impact on production. The water quality
parameters of primary concern are dissolved oxygen, ammonia, nitrite, carbon
dioxide, and gas supersaturation from either oxygen or nitrogen. 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. Upper limits for continuous exposure to the common metabolites
(ammonia, carbon dioxide, nitrite), pH, and chlorine should not exceed general
standards for fish culture as given by Piper (1982) and Meade (1989): Unionized Ammonia
    <0.0125 to 0.02 ppmCarbon Dioxide
    <10 ppmNitrite
    0.1 ppm in soft water, 0.2 ppm in hard waterpH
    6.5-8.0 These values are guidelines, they should not be interpreted to
mean that concentrations slightly above 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. High pH (>9.8) may be
lethal to walleye in the absence of ammonia, but pH as low as 8.3 shifts the
equilibrium of ammonia to the unionized form (NH3) that is more toxic to fish. 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, cadmium), chloramines, or free chlorine, or
toxic residues from toxic paints or sealants. Case studies The case studies by Colesante (1996), Moodie and Mathias (1996),
and Moore (1996) provide contrasting strategies for production-scale intensive
culture of walleye fry.  Colesante uses brine shrimp for 30 days, followed by 14
days of mixed feeding 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 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.  Lets Get Tanked The MTAN was very impressed with the new aluminum fish distribution
tanks now being manufactured by Aquaneering
Inc..  The pictures below show a small unit that was built for the Iron
River National Fish Hatchery.  The tank can easily fit inside a pickup
truck.  This live haul tank measures 46" by 48" by
30."  Although many options are available, this unit includes two
compartments with 6" camlock discharge pipes, oxygen injection system and
flowmeters, two Point Four diffusers, Fresh Flow pumps and lifting tugs. New aluminum fish distribution tanks now being manufactured by Aquaneering Inc.
      New aluminum fish distribution tanks now being manufactured by Aquaneering Inc.New aluminum fish distribution tanks now being manufactured by Aquaneering Inc.
      New aluminum fish distribution tanks now being manufactured by Aquaneering Inc.
 **Return
to MTAN selection pageReturn to Ashland NFWCO home pageReturn to Region 3 U.S. Fish and Wildlife Service**
Product and company
      names mentioned in this publication are for informational purposes only.
      It does not imply endorsement by the MTAN or the U.S. Government.
 Last updated: 
		  November 19, 2008
		Ashland Home | Midwest Region Home
		U.S. Fish and Wildlife Service Home Page | Department of the Interior 
			 | USA.gov  | About the U.S. Fish and Wildlife Service  | 
			Accessibility  | Privacy 
			 | Notices  | Disclaimer 
			 | FOIA
 Find Office By ProgramAdministrationEcological ServicesExternal AffairsFisheriesLaw EnforcementMigratory BirdsRefugesState Programs