United States

Department of Agriculture

CooparaUve

Stale Research
Senice

Extension Service
and Land~Grant University
Cooperating Extension

s.rn""

Cooperative Extension Service, The

Trout
Production
by James L. Shelton, Assistant Professor, Wamell School of Forest Resources
edited by George W, Lewis and Ronnie 1. Gilbert, Cooperative Extension
Service, The University of Georgia College of Agricultural and Envirorunental
Sciences

Univel~ity

of Georgia College of Agricultural and Envirorunental Sciences, Athens

This material is based upon work supported by the Cooperative State Research Service and Extension Service, U.S.
Department of Agriculture, under Special Project No. 87-EXCA-3-0836.

15

Trout Production
Trout Farming is the oldest fonn of commercial fish
production in the United States. Trout farming dates
back over 400 years in Europe and about 150 years in
the United States.
Trout are fanned both for food fish and for stocking
recreational fisheries. Rainbow trout (0 nco rhy11 Chils
rnykiss), is the most commonly raised species. Brown
trout (Salrna trulta), and brook trout (Salvelinus fantinalis), are also farmed. There are several subspecies
and strains of each species. For example, Shasta and
Kamloops refer to domestic strains of rainbow trout.
Rainbow trout were originally native to North
American rivers draining into the Pacific ocean.
Due to their popularity as a sportfish and as a food
fish, trout have been widely distributed and are now
cultured in waters around the world. The brown trout
is a native of European waters. Like the rainbow
trout, it has also been widely distributed. Brown trout
were first brought to the United States over 100 years
ago and are now present throughout North America.
Brook trout originally are native to an area that
extends from the northeastern coast of North America
west to the Great Lakes and south along the
Appalachian mountains as far as northern Georgia.
There are migratOly races of both rainbow trout and
brown trout which spawn in freshwater and migrate in
the same manner as salmon.
Trout are generally cultured in raceways or ponds
supplied with flowing water. However, some are produced in pens, nets and recirculating systems.
CURRENT STATUS
According to USDA's annual survey of trout producers, total sales of trout for 1992 were about $67.0
million (food-size fish, $53.0 million: stockers (6 to
12 inches in length), $6.7 million: fingerlings, $1.4
million and eggs, $5.8 million). While Idaho grows
over 70 percent ofthe total trout production annually,
trout farming operations exist throughout the United
States (Table I).
'
Trout eggs are typically produced on broodfish
farms. Trout egg production for the United States is
primarily concentrated in the western region (Table
2).

Table 1,1992 Trout Production: Number of

Operations and Total Pounds from U.S, Farms, ,+
Number of
Operations Food-Size Stockers Fingel'lings

State
California

Colorado
Idaho
Michigan
Missouri
New York
North Carolina
Oregon
PeJllsylvania
Tennessee
Virginia
Washington
Wisconsin
Other
Total
1

23

2.270

266

20

33
30
54
14
37
68
26
45
13
26
32
48
12'
461

310
41,500
600
578
106
3,874
400
2,470
316
969
222
374
2,255'
56,264

695

23

200
160
89
154
33
432
29
81
118
199
829'
3.285

61

Otherlncfudes GA and

7
7
3

12
12
15

6
127'
293

ur

other Includes GA. UT. and ID

3 Other includes GA. 10. MO. TN. and

ur

Aquaculture Situation and Outlook. Commodity Economics

Division. Economic Research Service. U.S. Department of Agriculture.
~Source:

March 1993. AQUA

10

Table 2. Trout Egg Sales for 1992 by Region. *

Region
Northeast
Central
West

Total
~Reglons

Numbe.. (l,OOO's)

$ Value (l,OOO's)

573
339
452.187
453.099

5
8,817
5,829

ara as follows: North East PA and NY

CentralMI. WI. GA. MO. NC. tN. VA

West-CO. 10. UT. WA
Source: Aquaculture Situation and Outlook. Commodity Economlc\
Division. Economic Research Service. U.S. Department of Agriculture,
March 1993, AQUAIO

Trout production in the United States has remained

relatively constant over the past few years. However.
from 1990 to 1992, the number of trout production
operations grew in Colorado. Idaho, Michigan,
Missouri, Pennsylvania, Tennessee and New York.
LIFE HISTORY
Trout belong to the group of fishes known as
Salmonids. Salmonids are cold water fishes, and
species cultured include Atlantic Salmon (Salrno

Figure 1. Rainbow Trout

salar), pacific salmon (Otlcorhytlchlls spp.), rainbow

trout, brown trout and brook trout. Salmon ids are

characterized by the presence of a small, fatty adipose
fin on the back between the dorsal fin and tail.
The typical coloration of rainbow trout is blue to
olive green above the lateral line, a pink band along
the lateral line and silver below the lateral line. The
back, sides, head and fins are generally covered with
small black spots. Brown trout are generally some
shade of brown on the back and side, fading to yellow
on the belly. Spots are large and dark (brown or
black). Spots are normally surrounded by pale halos.
Brook trout are best identified by the heavy velmiculations (wavy or winding lines) on the back.
Background color can be anywhere from light blue to
dark green. Lighter spots (red and yellow) cover the
body, the red spots being surrounded by pale halos.
(See Figure I.) Table 3 gives ranges of temperatnre
for survival, optimum growth and spawning of trout.

ed with the headwaters of river systems). Wild trout

sexually matnre at three years (two years for domestic
brood stock). The act of natnral spawning often
begins with an upstream migration of anywhere from
a few hundred feet to over a thousand miles. Once
trout arrive at their spawning grounds, females begin
digging circular beds in the gravel bottom. During the
process, the female will select a mate. The male will
then begin guarding the bed and defending the female
against other males. At the time of spawrring, the
female positions her vent at the bottom of the bed and
the male darts along side her. The female releases her
eggs and simultaneously the male, whose vent is in
close proximity to that of the female, releases Ins milt
into the bed. After the milt releases, the sperm must
fertilize eggs witlrin less than one minute, or the
sperm becomes inactive.
Immediately following spawning, the female
sweeps gravel into the bed to cover the eggs. The time
required for the eggs to hatch depends mainly on
water temperature (Table 4.)
Table 4. Number of Days Required for Trout Eggs
to Hatch and the Number of Eggs Produced Per
Pound of Female Bodywight. *
WATER TEMPERATURE
Species "'eight 3S Q F 40F 4S Q F SOQF5S0F60oF
Rainbow
Brown
Brook

1000

1000
1200

156
144

80
100
103

48
64

31
41

68

44

24

19

35

*Source: Trout and Salmon Culture, 1980. E. Leitritz and RC. Lewis.
Division of Agricultural Sciences. University of Califomia.

Table 3. Ranges of Temperature for Survival,

Otimum Gl'Owth and Spawning of Trout.*
Species
Rainbow trout
Brook trout
Bro\,n trout

Survival
33-78()
33-72()
33-78()

n)

Optimum
Spawning ('F) Growth (OF)
50-60()
45-55()

4860'

50_55
45_55
48_55

*Sotlfce: Fish Hatchel)' Management, 1982. KG. Piper, I.E. McElwain,

L.E. Orme, J.P. McCraren, L.G. Fowler and J.R. Leanard. United States
Department ofInterior, U.S.F.W., Washington, D.C.

Wild rainbow trout generally spawn from Januruy

to May and wild brown and brook trout from October
to January. Howevel', considerable variation in
spawning season results from climatic and genetic
differences. Through many generations of selective
breeding, hatchery strains of trout have been developed that spawn throughout the year. Tins means that
dependable year-round supplies of trout eggs are
available.
In nature, trout spawn in cold, well oxygenated
streams with gravel bottoms (areas typically associat-

SITE SELECTION AND DEVELOPMENT

A major factor in determining the chance of success
for any aquacultnre endeavor is location. The basic
characteristics of salmonids outlined in the section on
life history indicate that specific criteria must be met
by a potential site for connnercial trout production. A
trout farm must have a dependable year-round supply
of high quality water. For this reason, a thorough
stndy of the water supply is the first step in assessing
the potential of any site production. A small trout
farm capable of producing up to 100,000 pounds of
trout per year will require a continuous water flow of
at least 500 gallons per minute. The quality of the
water, and the topography of the site will be important
in determining actual production levels. Table 5 contains some basic water quality criteria for trout hatch
ery water supplies.

important to consider all local, state and federal laws

which may apply to the use of a water source or to
water discharge.
Table 5. Water Quality Criteria for Trout
Hatchery Water Supplies.
Desirable Level
Parameter

Figure 2. Production Raceways

Dissolved oxygen
Carbon dioxide
Temperature
pH
Total Alkalinity (as CaeOl)
Manganese
Iron
Zinc

Ground water is an excellent source of water for

trout production in areas where it is shallow enough
to make pumping economical or where artisan wells
occur. Some ground water sources are low in dissolved oxygen and high in hydrogen sulfide and will
require aeration before use. Well water can also be
supersaturated with dissolved nitrogen which can
cause a condition known as gas-bubble disease in
fish. This disease results from small gas bubbles
forming in the blood of the fish and blocking normal
circulation. Aeration will also remove supersaturated
nitrogen from water.
In areas where ground water is not available, stream
water can be used for trout production. However, temperature and flow fluctuation must be taken into
account when estimating production capacity.
The type of production units (concrete raceways
versus earthen ponds) and the number of water reuses
possible will vmy based on the specific characteristics
of a site. For example, in areas where water pH is low
(6.5 to 7.0), it is possible to reuse water six or more
times before unionized ammonia reaches toxic levels.
However, in alkaline water where pH values are 8.0 01'
above, only limited water reuse may be possible.
Obviously, land slope is also important in determining
the number of raceways or ponds that can be built in
series to allow gravity flow from upper ponds to the
ones below. (See Figure 2.) A minimum fall of 18
inches is recommended between raceways to provide
aeration of water. The greater the fall between units,
the more dissolved oxygen available for subsequent
water uses.
Trout production units are typically 6 to 10 feet
wide, 35 to 100 feet long and 3 to 4 feet deep. The
actual dimensions of a facility will depend on available water flow and topography. Where possible, tank
construction in pairs with a shared center wall will
greatly reduce construction costs.
In planning and developing a trout farm, it is

copper

near satumtion
<2.0 ppm
45-65F
6.5-8.5
10-400 ppm
<0.01 ppm
<l.Oppm
<0.05 ppm
<.006 ppm in soft ",aler
<0.3 ppm in hard 'vater

PRODUCTION METHODS
Hatchery Production
Hatchery production of trout eggs requires a high
degree of skill and is velY labor intensive. Egg production requires the maintenance of an adequate number of good quality broodfish at low stocking
densities.
SPAWNING
Artificial spawning of trout requires sorting brood
fish and selecting only fully mature (ripe) females.
Broodfish are normally starved for three 01' four days
prior to stripping. This prevents fecal contamination
during fertilization. TIle eggs of ripe females will
flow freely fi'om the vent under gentle pressure. Ripe
females should always be held tail down with the
head high. This permits the eggs to flow down the
oviduct toward the vent.
The use of anesthetics during stripping can simplify
handling and minimize stress to broodstock.
Stripping of eggs requires two people. One person
firmly holds the fish near the head with one hand and
just in front of the tail with the other (head up). The
fish is held with the belly downward over a collection
pan. A towel will help in handling wet, slippely fish.
The second person gently dries the belly of the female
and then begins to stroke the belly, stmting near the
pelvic fins and moving back toward the vent. An
alternate method of egg removal is air spawning. A
rubber hose is used to connect a large dimneter hypodermic needle to a low pressure (2 psi) air compressor. TIle needle is inserted about Y, inch into the body
cavity of the female nem' the pelvic fms. The low

Figure 3. Eyed Stage-Trout Eggs

pressure air pushes the ripe eggs out the vent. After
stripping, the air must be removed from the body cavity by gently massaging the sides of the fish. Air
spawning is reported to be less stressful to broodfish
and produces cleaner, healthier eggs.
Once the eggs are collected, milt is added to the
bowl. Males are stripped in much the same way as
females. Again, the belly of the fish is first dried,
placed over the bowl containing eggs or over another
container and stroked gently from front to back. Eggs
from more than one female can be collected in one
container, and more than one male should always be
used to insure good fertilization. The eggs and milt
are mixed thoroughly, and water is added to activate
the sperm. As soon as water is added, the eggs begin
to absorb it, swell and become fum. This process
generally takes about 20 minutes and is known as
water hardening. Eggs increase in size about 20 percent during this process.
Water hardened eggs can be transported for a period of up to 48 hours after feliilization. After the initial 48-hour period, eggs should not be moved until
they reach the eyed stage (the eyes become visible
through the egg shell.) (See Figure 3). Trout eggs are
usually shipped during the eyed stage. Trout eggs
must be shielded from direct light during all stages of
development.
EGG INCUBATION

Three types of egg incubation systems are commonly used: hatching troughs, vertical flow incubators and hatching jars.
A hatching trough is a horizontal channel with
water being piped in at one end and drained out at the
other. Wire baskets or screened trays (California
trays) are suspended within the trough. A partition is
placed between each tray or basket which forces
water to flow up through the eggs from below before
spilling over into the next compartment.
Veliical flow incubator systems involve stacking 8
to 16 trays on top of each other in specially designed
racks. Water is introduced at one end of the top tray

and flows up through the screen bottom, circulating

through the eggs. The water then spills over into the
tray below and is aerated as it drops.
Hatching jars are available commercially or can be
constructed ft'om PVC pipe, five gallon plastic buckets or other materials. The jars are cylindrical and
water flows in through a hose or tube at the bottom,
upwells through the eggs and spills over the top. The
water movement suspends and gently rolls the eggs in
the circulating water.
Trout eggs should be placed in baskets or trays no
more than two layers deep in order to allow adequate
water circulation. Flow rates for veliical or horizontal
tray incubators are 4 to 6 gallons per minute (gpm).
Hatching jars should contain no more than ';, of the
total volume in eggs. The flow rate for each jar
should be adjusted so that eggs are lifted to 50 percent
of the standing depth of eggs when flow is shut off.
For example, if a hatching jar is ftlled with eggs to a
depth of 10 inches when the water flow is shut off, the
flow rate should be adjusted so that eggs upwell to a
depth of 15 inches with water on.
Buying Trout Eggs
Most trout farmers buy eggs rather than producing
their own. Trout eggs should be purchased fi'om a
supplier whose hatchery is "certified disease ftee."
Suppliers should disinfect eggs before shipping, but
they should be treated again upon arrival. Trout eggs
will arrive packed in boxes designed to keep them
moist and cool. Eggs should be tempered gradually
to the temperature of the hatchery. This is done by
transferring eggs to a clean container and adding
small amounts of clean hatchery water over a period
of 30 minutes to I hour. The eggs should be gently
stuTed a few times during the process to ensure adequate water circulation. Egg shipping containers
should be discarded or destroyed to prevent possible
contamination of the hatchery with disease causing
organisms.
Disinfectants used for treating eyed trout eggs contain iodine. Various brand names and concentrations
are available. Treatment should be at a rate of 100
parts per million (ppm) offi'ee iodine for 10 minutes.
Label concentrations of iodine are often given as a
percent active ingredient.
In soft or acid waters (alkalinity below 30 ppm) egg
mortality can result from pH reduction by iodine
treatment. Baking soda (sodium bicarbonate) should
be added as a buffer at a rate of20 grams (0.7 ounces)
per 10 gallons of water. Eggs and disinfecting solution should be mixed together gently to assure thor-

ough coverage. After 10 minutes pour off the disinfectant and rinse eggs in fresh hatchery water to
remove residual iodine before transferring eggs to
incubators.
Fungus will grow rapidly on dead trout eggs and
can spread to live eggs. During the incubation process. dead eggs should be removed regularly. If fungus becomes so widespread that siphoning off dead
eggs becomes too time consuming, formalin can be
used. Formalin is added to the water flowing into
incubators at a rate of I part formalin to 600 parts
water for a duration of 1.5 minutes daily. This translates to 95 ml. (3.2 fluid ounces formalin for every
gpm of water flow). Do not treat trout eggs with formalin within 24 hours of hatching or high mortalities
will likely occur.

Fry Rearing
The number of days required for eggs to hatch
depends on water temperature (Table 4). Once hatching begins, eggs and fry should not be treated with
any chemicals. Empty egg shells should be removed
from incubation units regularly. All eggs in a batch
will usually complete hatching within three to four
days. Trout emerge fl'om eggs with a reserve of food
in a yolk sac. At this stage, they are referred to as sac
fry and will continue to feed on their yolks for 2 to 4
weeks, depending on water temperature. If trout eggs
were incnbated in containers other than rearing
troughs, sac fry should be transferred to troughs
shortly after hatching is complete. Dead and deformed fry should be removed daily. Troughs for fly
rearing al"e typically 12 to 16 feet long, 12 to 18 inches wide and 9 to 12 inches deep. Fry should be
stocked at a rate of 1,000 to 2,000 fry per square foot
of trough surfuce area. The actual stocking density
for a system will depend on the flow rate and water
temperature. Typically, \0 to 1.5 gpm flow is used for
fry trough systems. The water level in the fry trough
should be kept quite shallow (3 to 4 inches) until the
fry begin to "swim up." Troughs should be screened
at the upper end to remove debris from inflow and
must be screened at the lower end to prevent fry from
being flushed out. "Swim up" refel"s to the stage
when fry have absorbed most of their yolk sac and
begin actively searching for food.
When about half of the fry reach the "swim up"
stage, begin feeding. Fry feeds should contain 48-50
percent crude protein and I 2 - 5 percent fat. Introduce a small amount of starter granules on the surface
tlu'ee or four times daily at flfSt. When most of the
fry are actively feeding, feed should be applied more

often (every 15 minutes if possible, but at least

hourly). Automatic feeders make frequent feeding of
fry much easier. For the first two to three weeks, it is
best to feed fry "by eye." In other words, apply
enough feed so that all fish have food available to
them, but do not overfeed to the point where an abundance of uneaten feed accumulates in the troughs.
When fry reach about M-inch length (about 2,500
fry/pound), begin feeding based on published feeding
charts (Table 6). Feeding charts are based on fish size
and water temperature. Uneaten feed should be either
swept out through the screen or siphoned off at least
daily, because decomposing feed will consume dissolved oxygen and produce anunonia, which is toxic
to fish.
Table 6. Recommended Feeding Rates for Small
Trout as Percent Body Weight. Numbers represent
total feed/day (divided evenly among the number
of feedings/day). *
Number ofFish per Pound
2500-800
800-300 300-100 100-30
2500+
Approximate Length (inches)
Water Temp.
0/0""1
1-1.5
1.5-2
2-3
34
(OF)
55
5.2
5.l
4.2
3.2
6.l
7.5
6.3
6.1
5.l
3.9
60
4.9
9.0
1.5
1.2
6.l
65
Starter
No.1
No.2
No.3
No.4
granule granule granule granule
Feed Sizes granule
No. Feedings!
8
4
8
6
day

*Source: Trout and Salmon Culture, 1980. E. Leitritz and RC.

Lewis. Division of Agricultural Sciences. University of
California.

When all fly in a trough have been actively feeding

for two weeks, begin taking a sample count every
week in order to adjust feeding rate, feeding frequency and feed size (Table 9). If fiy are being fed properly, grading is not necessmy; but fry may need to be
"thinned out" as they grow in order to prevent overof the water
crowding. Spread feed over the upper
surface area so that all fry have a chance to obtain
sufficient food. If dissolved oxygen levels fall below
6 ppm at the lower end of a trough, reduce the weight
of fish in the trough.
When fry reach 200 to 250 per pound (about 2
inches), they are ready for transfer to larger, deeper
fmgerling tanks. Taaks for fingerling growout m'e
constructed of a variety of materials (fiberglass, aluminum, concrete blocks, etc.) and are either circular
or rectangular.

2"

FOOD FISH PRODUCTION

Fish are generally held and fed in fingerling tanks
until they reach about 3 inches in length (about 100
fish per pound.) At this time fish are moved to outdoor raceways or earthen ponds for final growout.
The maximum amount of fish that can be held in a
rearing unit (tank, raceway or pond) is referred to as
carrying capacity. The actual carrying capacity of a
culture unit depends on water flow rate, water volume, water temperature, dissolved oxygen concentration, pH and fish size. Carrying capacity is expressed
in terms of weight of fish per unit water volume
(pounds fish per cubic foot or pounds fish per gallon)
or in terms of weight of fish per unit water flow
(pounds fish per gpm or pounds fish per cubic foot
per second (cfs)).
A common method for estimating maximum carrying capacity in a tank or raceway is the Density Index
(D). The Density Index is a factor which, when multiplied by rearing unit volume in cubic feet (V) and by
fish length in inches (L) will give the maximum
allowable weight of fish (W):
W=DxVxL
As a rule of thumb, 0 for trout should be from 0.4
to 1. In other words, fish densities (pounds of fish per
cubic foot of tank space) should be no greater than
0.5 to 1 times their length in inches (Table 7). For
example, if a 0 factor of 0.5 is used, 2-inch fish could
be held at a density of 1 pound per cubic foot (0.5 x
2). If a 0 factor of I is used, 2-inch fish could be
held at a density of2 pounds per cubic foot (lx2).
Table 7. Maximum Density (pounds per cubic feet)
of Trout of Various Lengths Based on Density
Index (D) Factors of 0.5, 0.75, and 1.0 That Can be
Held in a Given Rearing unit.
D factor

0.50

1.0

2.0

0.75

1.5
2.0

3.0
4.0

1.00

Fish length Ouches)

6
8
4.0
3.0
4.5
6.0
6.0
8.0

12

6.0
9.0
12.0

While the 0 is useful in estimating carrying capacity, it considers only space (pounds of fish per unit
volume). Another velY important consideration in
establishing carrying capacity is flow rate. The flow
rate determines how rapidly fresh water will replace
"used" water (water in which fish have reduced dissolved oxygen concentrations and excreted waste
products).

The Flow Index (F) takes flow rate into consideration when estimating maximum allowable weight of
fish that a culture unit can hold:

FxLxI

Where W = maximum allowable weight of fish

(pounds)
F= Flow Iodex
L= Length of fish in inches
1= Water inflow (gallons per minute)
As a rule of thumb, F values for trout raceways
range from 0.5 to 1.5. Actual F values will depend on
several mctors, especially the dissolved oxygen concentration of the inflowing water. To estimate the
Flow Iodex for a specific culture unit, fish are added
while water flow is held constant. When enough fish
have been placed in the system so that the dissolved
oxygen level of the outflowing water has been
reduced below 6 ppm, the unit is at maximum. F will
then be equal to this value in pounds divided by the
average fish length in inches times flow rate in gpm:
F= W
LxI

Once the F value has been established for a culture

system, the previous equation can be used to determine canying capacity for various flow rates and various sizes of fish.
Example: 600 pounds of 4-inch trout held in a raceway with a flow rate of 150 gpm cause the dissolved
oxygen concentration of the outflow to decline below
6.0 ppm. Calculate the F and use it to determine (a)
how many pounds of 6-inch fish can be held and (b)
what (1) would be required in order to hold 400
pounds of 4-inch trout.
Solution: The Flow Index is calculated using the
equation given above:
F = ~ _ 600
= 1.0
Lxi
4x150
(a) We can determine carrying capacity (W) for the
system using 6-inch fish:
W=FxLxl= 1.0x6x 150=900pounds
(b) Next we can determine water flow rate (I)
needed to hold 600 pounds of 4-inch fish:

Grading and Inventory

I =~W_- 400 = 100 gpm
FxL
1.0x4
It is important to remember that the Flow Index
concept operates on the assumption that inflowing
water is saturated with dissolved oxygen. If the
inflowing water is below saturation, carrying capacity
will be reduced proportionally. When trout production facilities are designed for optimal use of space
and water flow, Flow Index and Density Index values
for a unit should be quite similar.
Overloading trout production units can result in
decreased dissolved oxygen and increased ammonia
levels. These conditions can reduce growth rates and
stress fish. The loading rates for culture units and the
number of water uses possible for raceway systems
will be set based on the allowable levels for these two
water quality parameters. Dissolved oxygen levels
should not be allowed to drop below 4 ppm. Dissolved oxygen levels should be monitored regularly.
The quickest method of making these measurements
is with a dissolved oxygen meter. Smaller farms may
use an oxygen test kit which is less expensive but
much more time consuming than a meter. Ammonia
occurs in two fOlms in water, ionized and unionized.
The ionized form (NH4') is much less toxic. The relative proportion ofthe two forms de-pends on the pH
of the water. At relatively low pH (6.5 to 7.0), most
of the ammonia present will be in the ionized (nontoxic) form. A more alkaline pH (>7.5) means that
most of the ammonia present will be in the unionized
(toxic) form. Total ammonia concentrations can easily be measured using a water quality test kit. However, the percent of the total present in the toxic form
will depend on the pH (Table 8).
Continuous exposure to unionized ammonia (NH,)
concentration above 0.03 ppm can reduce growth
rates. The more times water is reused, the more likely
it is that this level will be exceeded. The number of
water uses possible in multiple-pass systems varies
from 3 to 10 times or more.

Table 8. Percent of Total Ammonia in the

Unionized (NH,) Form in Freshwater at Varying
pH and Water Temperatures.
pH
7.0
7.5
&.0
8.5

TEMPERATURE
50'r
60'F
0.19
0.59
1.&3
5.55

0.27
0.&5
2.65
7.9&

68'F
0.4
1.24
3.83
11.18.

From the time lingerlings are stocked in raceways

(about 3 inches) until they reach marketable size (12
to 16 inches), they must be graded periodically.
Grading allows fish to be sorted into similar size
groups and improves feeding efficiency. Trout are
typically graded four times during a production cycle,
but this will vary depending on the specific conditions
of each culture unit. Some falmers grade when the
length of the shortest fish in a tank is less than 50 percent of the length of the longest fish.
Graders consist of a rectangulal' frame with evenly
spaced bars (aluminum tubing, PVC pipe or wooden
dowels) across it. The grader should be as long as the
raceway is wide, and slightly taller than the water is
deep. The grader is placed in the inflow end of the
raceway and moved toward the outflow end. This
crowds the larger fish in the outflow end so they can
be removed and stocked in another raceway with fish
of similar size. Fish should be graded whenever the
loading rate for a culture unit is approached and density needs to be reduced.
Keeping track of the quantity and size of fish in
each culture unit on a farm is important because it
allows a farmer to estimate growth rates, feed conversions, production costs and how near each unit is to
carrying capacity. Sampling should be done at least
once, and preferably twice, per month. In sampling
raceways, fish are generally crowded starting at a distance from the outflow equal to one-third the total
length of the tank and moving toward the inflow.
This is done to avoid sampling the smaller, weaker
fish which tend to school near the outflow. When the
fish are concentrated near the inflow end of the tank,
a sample is taken with a dip net and either weighed in
the net or transferred to a bucket of water (of known
weight) and weighed. As the fish are poured back into
the raceway they are counted and the weights and
counts recorded. Three or four samples of at least 40
fish each should be taken from different areas of each
tank.
Dividing the number of fish in each sample by the
weight of the sample will give fish size expressed as
number of fish per pound. This value can then be
multiplied by the original number of fish stocked in
the raceway, less any mortalities, to give the total
weight of fish in a unit. Table 9 shows the relationship between weights and lengths for rainbow trout of
various sizes. It is important to remember that these
numbers are averages and the actual relationship
between length and weight will vary depending on the
condition of the fish.

Table 9. Length Weight Relationships for Tront. *

Length (inches)

No./pounds

weightll ,000 fish (polmds)

3
4
5
6
7
8
9
10
11
12

98.0
39.8
19.8
11.2
6.9
4.5
3.1
2.2
1.6
1.2

10.2
25.5
50.4
X9.2
144.9
222.2
322.1
454.6
625.1
833.3

*These munbers are averages

It is more difficult to keep track of fish quantity and

size of fish in earthen ponds. Some farmers use emihen ponds only to grow out stockers (4 fish/pound) to
marketable size with no grading. Other farmers sample count fish in emihen ponds by throwing a few
handfuls of feed into ponds and throwing a cast net
over the feeding fish. Fish are then weighed, usually
in the net, and counted back into the pond. This
method typically yields biased results since the larger,
more aggressive fish will come to feed first.

Feeding Practices
The cost of feed is the major variable cost in producing trout. Growout diets for trout should contain
about 40 percent protein and 10 percent fat. Several
brands of high quality trout feed are available commercially. While the obvious goal in feeding is to get
fish to marketable size as quickly as possible, feeding
efficiency is critical in determining overall farm profits. Efficient feeding means always giving fish slightly
less than the maximum amount they will eat. This
will result in an optimum rate of fish growth, uniform
fish size and maintenance of good water quality.
The best guide to determining the COlTect size and
amount of feed needed is a published feeding chart
provided by feed manufacturers. Using this chart as a
reference, a farmer should adjust actual feeding rates
based on specific conditions on the farm. Feeding
charts give the approximate amount of feed (pounds
of feed per 100 pounds of fish or as a percentage of
the total weight of fish) for a specific size fish at a
specific water temperature.
Once fish are stocked in raceways or earthen ponds,
hand-feeding alone is usually not practical, except
when administering medicated feed to sick fish.
Trout should be fed seven days per week under normal circumstances. A variety of automatic feeders
are available, including electric, water and solar powered units. These feeders deliver feed at preset inter-

10

vals. Feed wagons are also available which use a

blower to deliver a large amollnt of feed as they are
pulled around the farm by a truck or tractor.
Many farms use demand feeders for the majority of
feeding. (See Figure 4). A demand feeder consists of
a conical hopper with a small opening at the bottom.
The small opening is covered by a movable disc
attached to a rod which extends into the water. The
lower end of the rod acts as a trigger, and trout learn
that striking the target causes feed to fall from the
hopper. Demand feeders reduce labor costs and allow
feeding activity to be spread over several hours. This
helps to insure efficient feed utilization and prevents
the rapid decline in dissolved oxygen and rise in
ammonia which can occur when a large quantity of
feed is applied at once. Demand feeders must be
adjusted periodically to prevent overfeeding. It is recommended that some feed be applied by hand each
day so that overall fish behavior can be observed.
This can be done when checking or loading demand
feeders. Since demand feeders can hold enough feed
for several days, careful records should be kept so that
the amount of feed going to each culture unit is
known. In loading demand feeders, remember that
trout can eat more than they can metabolize.
Therefore, it is important to add feed based on the
amount of feed trout should be eating daily based on
fish size, water temperature and personal experience.
Just filling the feeders when they are empty can result
in poor feed conversion ratios.
Sampling records are used to adjllst feeding rates
and check feed conversion rates. Feed conversion
rates for trout are generally between 1.2 and 2.0
pounds of food per pound of weight gain. Remember
to include daily weight gain when calculating daily

Figure 4. Demand Feeder

feeding rates.
Because trout are cold-blooded animals, their
metabolic rate depends on water temperature. The
minimum temperature for growth in trout is about
38F. At or below this temperature, only a maintenance feeding level is needed (0.5 to 1.8 percent body
weight per day, depending on fish size.) At these
water temperatures, no feed for a day or two will not
harm fish. Optimum growth for trout occurs between
55' to 65F. When water temperature exceeds 65'F,
feeding time, feeding frequency and amount of food
per feeding should be adjusted based on dissolved
oxygen levels. At water temperatures above 68F, a
trout's digestive system becomes inefficient and much
of the nutrient content of the feed ends up as waste in
the water.
Certain markets for trout require diet modifications
to produce salmon-colored flesh. Carotenoid pigments (canthaxanthin) added to feed impart a pink or
red coloration to flesh when used for 3 to 6 months
(depending on water temperature) before harvest.
In order to minimize stress, fish should not be fed
for a period prior to handling or transport. For routine handling, such as grading, 24 hours without food
is sufficient. For long distance transport or processing, feed should be withheld for 3-4 days.
FISH HEALTH
Diseases can be divided into two categories; noninfectious and infectious. Noninfectious diseases
include nutritional disorders, contaminant exposure
(pesticides or heavy metals) and exposure to toxic
metabolites (ammonia and nitrite.) Infectious diseases
include parasitic, bacterial and viral infections.
Noninfectious Diseases
Nutritional disorders like anemia can result fi'om
improper storage of feed and feeding old, moldy feed.
Fish feed should always be stored in a cool, dry place
and purchased in quantities small enough to be used
quickly.
Chronic exposure to ammonia can result in poor
growth. When fish densities and feeding rates are
heavy, ammonia levels should be monitored regularly
with a water test kit. Remember that water pH will
determine the toxicity of ammonia. While ammonia
exposure doesn't usually kill fish directly, it is a
sOUl'ce of stress.
Stress plays an extremely important role in the
onset of a disease problem. Under normal conditions,
the immune system of a fish is able to fight off most
infectious disease agents. However, when a fish

becomes stressed. the effectiveness of the immune

response is diminished. Sources of stress include
improper or excessive handling. sudden changes in
water temperature, low dissolved oxygen, high
ammonia levels, poor nutrition and overcrowding.
Most infectious disease outbreaks occur afier fish
have been exposed to one or more of these stressors.
Infectious Diseases
Diagnosis of infectious diseases in trout should be
performed by a trained fish diaguostician. Accurate
identification of causative agents usually involves the
use of sophisticated equipment not readily available
on most fish farms. A farmer should be familiar with
the procedure for quickly getting sick or dead fish to
the nearest diagnostician.
There are three main viral diseases oftrout: infectious pancreatic necrosis (IPN), infectious hematopoietic necrosis (IHN) and viral hemorrhagic septicemia
(VHS). All these are most harmful to young trout, and
moralities can be very high. Infectious hematopoietic
necrosis and VHS can affect older trout, but moralities are much lower than with young fish. All three
disease can be transmitted by contaminated eggs.
There are no effective treatments for theses viral diseases. Prevention involves purchasing only certified
disease-free eggs (or using only certified broodstock)
and disinfecting eggs at the eyed stage.
There are three categories of bacterial infections
which affect trout; acute systemic. chronic systemic
and acute external. Because diseases within each category exhibit similar symptoms, laboratory diagnosis
is essential.
Acute systemic bacterial infections include enteric
redmouth (ERM), furunculosis and bacterial hemorrhagic septicemia. The recommended treatment for
these diseases involves feeding one of the FDAapproved antibacterial drugs according to label directions. In areas where ERM has been reported,
fingerlings should be vaccinated 7 to 10 days before
moving fish into raceways.
Chronic systemic bacterial infections include bacterial kidney disease (BKD), which is slow to develop.
Once established, it may be impossible to cure. There
is no FDA-approved treatment for infected food fish.
Strict quarantine and careful disposal of infected fish
are recommended.
Acute external bacterial infections include columnaris disease which typically affects stressed fish.
especially at high water temperatures. The recommended treatment involves applying an FDAapproved chemical to the water according to label
directions.
II

Hatchery Sanitation

ECONOMICS

Great care should be taken to prevent the introduction of disease-causing agents into hatchery facilities.
The best way to do this is to restrict movement of
nonessential personnel. A disinfectant footbath should
be placed inside the entrance at all times. Under no
circumstances should equipment used in the hatchery,
such as nets or buckets, be removed. The hatchery
building and all equipment should be periodically
cleaned and disinfected using a chlorine bleach solution.

If a suitable site for trout production can be identified, it is reasonable to develop a financial budget.
Most lending institutions will require a detailed economic feasibility study. Development costs and production costs vary greatly from site to site. Tables 11
and 12 may be useful in estimating development costs
for a trout raceway system.
Table 11. Worksheet for Estimating the Cost to
Develop a Trout Raceway System.
Category

MARKETING

Quantity

Price

Units

Value

Site preparation _ _ _ _ _ _ _ _ _ _ _ _ _ __

The time to investigate marketing strategies for

trout is well before construction of facilities begins.
Potential markets for falm-raised trout include live
haulers, fee-fishing operations, sales to other producers, direct sales to customers, processors, restaurants
and retail outlets. Table 10 shows the relative importance of each of these outlets for the United States in
1992. Percentages may valY greatly fi'om state to
state. For example, 98 percent of all trout produced in
Idaho during 1992 were marketed through processors,
while in Michigan 26 percent went to fee-fishing, 23
percent to processors and 15 percent to restaurants
and retail outlets.

Concrete floor
Reinforcement
Drain pipe

Screening
Tank fonns

Labor
Miscellaneous

Total

Production costs of $0.60 to $ 1.1 0 per pound have

been reported for trout production facilities. Table 12
may be useful in estimating the operating costs of a
trout farm.

Table 10. Percentage of Food-Size Trout Sold by

Outlet Type
OUIlet
Live Haulers
Fee Fishing
Other producers
Direct to consumer
Processors
Restaurant and retail
Other

%
4
16

Table 12. Worksheet for Estimating Annual

Operating Budget of a Trout Raceway System.
Category

2
71
J
I

Developing a marketing strategy will require careful investigation of the local feasibility of each of
these alternatives. A producer must determine:

Units

Operation inputs
Eggs or Fingerlings
Standard feed
Medicated feed
Chemicals
Electricity
Equipment repairs

3. what are the product form and size preferences

Total Variable Cost

Capital Costs
Annual operating capital
Development investment
TOTAL INTEREST CHARGE

4. is there room for

O\'mership Costs
(depreciation, taxes, insurance)

I.

who is buying trout and at what price

2. how much of a demand exists

growth

Price

Gross Receipts
(Trout)

LaPor Costs
Returns to Land, overhead and management

12

Quantity Value

REFERENCES AND ADDITIONAL INFORMATION

If you are a new or prospective trout farmer, not

only will you need information concerning production
management techniques, you may also need information concemiog processing, marketing, economics,
financial assistance, disease diagnostic services, water
quality analyses, aquatic weed control, local and state
laws and regulations, site selection and development,
etc. In some areas, locating this information can be
difficult. The following are possible sources of information or assistance.
1. The county Cooperative Extension Service office,
usually listed under "County Government" in the telephone directory, can provide assistance. County
Extension agents are employees of land grant universities. The county agent may assist you directly or
draw upon the experience and training of a university
expert or refer you to some other state or federal
agency who can provide you with the information or
service you need.

2. In the coastal and Great Lake states, land grant universities also have Sea Grant programs. In many of
these states, marine advisory service specialists can
provide needed information.
3. State game and fish agencies may also be a source
of information on laws and regulations, production
technology and diseases.

5. The United States Department of Agriculture's five

Regional Aquaculture Centers can also refer you to
state specialists for other resources specific to your
needs.
Center for Tropical and
Subtropical Aquaculture
'The Oceanic Institute
Makapu'i Point
Waimanalo. III %795
North Central Regional
Aquaculture Center
Room 13 Nat Res. Bldg.
Michigan. State University
East Lansing, MI 48824 1222

Southern Regional
Aquaculture Center
Delta Branch Experiment Station
P.O. Box 197

Stoneville. MS 38776

Western Regional
Aquaculture Consortium

School of Fisheries. \VH 10

University of Washington
Seattle. WA 98195

Northeast Regional
Aquaculture Center
University of Massachusetts-Dartmouth
R=h201
North Dartmouth, MA 02747

6. The United States Department of Agriculture

National Agriculture Library is the National
Aquaculture Information Center. It provides informational services on aquaculture. The address is:
U.S. Department of Agriculture
Aquaculture Information Center
Room 304 National Agriculture Library
10301 Baltimore Boulevard
Beltsville. MD 20705

4. The United States Department of Agriculture Soil

Conservation Service can assist in site selection and
facility development. This agency is usually listed in
the telephone directory under "federal" or "United
States Government."

13

REFERENCES
Hinshaw. J.M. 1990. Trout Farming Handling eggs and
fry. Southern Regional Aquaculture Center Publication
220. Stoneville. MS.
Hinshaw, J.M., L.E. Rogers and J.E. Easley. 1990.
Budgets for trout production estimating costs and
returns for trout farming in the south. Southern
Regional Aquaculture Center Publication 22 I,
Stoneville, MS.
Hinshaw. J.M. 1990. Trout Fanning A guide to produc-

tion and inventory management. Southern Regional

Aquaculture Center Publication 222, Stoneville. MS.
Hinshaw. J.M. 1990. Trout Farming Feeds and feeding
methods. Southern Regional Aquaculture Center
Publication 223, Stoneville, MS.
Kain, K. and D. Garling. 1993. Trout culture in the North
Central Region. North Central Regional Aquaculture
Center Publication 108, Michigan State University, East
Lansing. Michigan.

14

Klontz, G.W. 199 1. A manual for rainbow trout production

on the family-owned farm. Nelson and Sons, Inc.
Murray, Utah.
Leitritz. E. and R.C. Lewis. 1980. Trout and Salmon
Culture. Division of Agricultural Sciences. University
of California.

Piper, R.G., I.B. McElwain, L.E. Onne, J.P. McCraren,

L.G. Fowler and J.R. Leonard. 1982. Fish Hatchery
Management. U.S. Department of Interior, Fish and
Wildlife Service. Washington. D.C. 1982.
Stevenson, J.P. 1987. Trout Farming Manual. Fishing
News Books Limited. Famham, Surrey, England.

78 S

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