Download Transportation of Warmwater Fish

SRAC Publication No. 392
.
Southern
Regional
Aquaculture
Center
June, 1990
Transportation of Warmwater Fish
Procedures and Loading Rates
Gary L. Jensen*
Experience and research have
shown that transportation
results can be improved by the
addition of certain chemicals.
Any chemical used should
produce an economical and
proven benefit. If food fish are
transported, only chemicals and
drugs approved by the Food and
Drug Administration can be
used. Tropical fish, ornamentals
and baitfish are not exempt from
this restriction.
Use salt for transport
Common table salt is widely
used in fish transport. It should
contain no iodine. The concentration of salts in the blood of most
fish is 1 to 1.2 percent. Adding
salt to the transport water
reduces the mineral difference
between the water and fish blood
which lessens the effects caused
by this osmotic imbalance. Salt
is added to make solutions of .05
Transport truck used to load live catfish.
* Louisiana Cooperative Extension
to 1 percent (500 to 10,000 ppm),
depending on the species of fish.
This is equivalent to 0.4 to 8
pounds of salt per 100 gallons of
water. Use the lower rates on
freshwater fish.
Use of anesthetics
Some species are very excitable
and sensitive to handling and
hauling stress. Anesthetics are
useful for sedating such fish, and
to reduce the metabolic activity.
This means less oxygen consumption and less carbon dioxide and
ammonia buildup. Also, energy
is conserved which is available
for maintaining ion balance. Fish
can be over-anesthetized and die.
Broodfish and species like redfish, largemouth bass, and
hybrid striped bass respond well
to anesthetics.
A popular anesthetic is MS-222.
It is approved for use on food
fish, and a 21-day withdrawal
period is required before fish are
consumed. The recommended
level of anesthesia during
transport should permit fish to
be caught easily by hand but not
cause total loss of activity or equilibrium. MS-222 is used at 15 to
66 ppm for 6 to 48 hours to
sedate fish during transport.
Red drum and hybrid striped
bass have been transported successfully with MS-222 with 10 to
20 ppm for up to 24 hours.
Water quality
considerations
Chronic fish losses or weak fish
problems are often associated
with handling and transporting
fish in very soft water (less than
10 ppm hardness). Hardness and
alkalinity levels from 50 to 100
ppm are preferable. Sodium
bicarbonate and calcium chloride
will increase alkalinity and hardness, respectively, are safe to use
and have no restrictions. Add approximately 5 grams per 100 gallons of water to increase the
alkalinity by 10 ppm. Add about
30 grams per 100 gallons to increase the hardness by 50 ppm.
Anti-foaming agents are used to
combat the formation of scum or
foam on the water surface. Foam
buildup interferes with observing
fish and may inhibit some gas exchange. Dow Corning’s 10 percent anti-foam AF®is used at 1
ounce per 100 gallons of water
and is nontoxic.
When fish are crowded, stressed
and excited, water quality can
deteriorate rapidly. Oxygen is an
important limiting factor in fish
transport. Proper aeration equipment and careful monitoring
before and during loading, in
transit and at unloading sites
will assure adequate levels (See
SRAC Publication No. 390).
Water temperature is important
in dissolved oxygen dynamics
and consumption rates by fish.
Cooling water reduces metabolism rates (oxygen consumption)
and increases the volubility of
oxygen in the water. Maintain
oxygen levels at 6 to 7 ppm but
higher levels may be beneficial
on extended trips.
Carbon dioxide will accumulate
during the trip, but high oxygen
levels, air circulation and water
agitation all help reduce any adverse effects. Ammonia can also
increase in hauling situations
and is not removed by agitation.
Starving fish before transport,
using clean water and lowering
the water temperature all help
reduce ammonia. The pH of hauling water should be 7 to 7.5;
higher pH increases the toxicity
of un-ionized ammonia. Well-buffered water helps keep pH in
balance.
Temperature critical factor
Temperature is very critical because it influences other water
quality variables. Inadequate
acclimation (tempering) for
temperature differences during
loading or unloading will stress
or kill fish. Temper fish at least
20 minutes for each 10 degrees
Fahrenheit difference in water
temperature. Some species are
very sensitive to temperature
shock, while others are quite
hardy. Smaller fish are more
sensitive than larger ones.
Rapid changes in pH, hardness,
alkalinity, temperature and
other variables may cause stress
or even death. It is advisable to
mix receiving water with hauling
water before releasing fish into a
pond. This tempering is recommended if the pH difference is 1
or more units or the temperature
difference is more than 10° F.
Fish loading guidelines
Load fish carefully into transport
units. Delicate fish should be
given mild sedation while in the
holding vat. Increase the oxygen
supply while fish are being
loaded. Check dissolved
oxygen (DO) in hauling unit to assure adequate concentrations
near air-saturation.
Do not overload dip nets or loading baskets. Fish should be handled rapidly, and delicate, scaled
species should be kept in water
whenever possible. Avoid the
warmest times of the day and
direct, bright sunlight. Minimize
the time out of water on windy
days when the drying effect is
greatest. Avoid injuries (broken
or damaged fins and scale loss),
which provide sites for opportunistic infections. Adverse effects from stress are additive and
cumulative. Salt, anesthetic or a
bacteriostat in the hauling water
can minimize stress.
Always avoid temperature shock.
Any sudden temperature difference of more than 10° F can
harm fish, particularly smaller
ones. Cold winter air and wind
chill factors can cause temperature shock when fish are moved
in nets.
To lower water temperature
about 10° F use ice at 1/2 pound
per gallon. Avoid using ice made
from chlorinated drinking water,
as some species are extremely
sensitive to chlorine. Lowering
the temperature during
transport quiets fish, lowers
their rate of metabolism and increases the oxygen saturation
level. For short trips, the hauling
temperature should be similar to
that of the water at the destination. For trips longer than 8 to
12 hours, tempering can begin
several hours before arrival.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with
the understanding that no discrimination
is intended and no endorsement by the
Cooperative Extension Service is implied.
This publication was supported in part by a grant from the United States Department of Agriculture. Number 87-CRSR-2-3218, sponsored
jointly by the Cooperative State Research Service and the Extension Service.
SRAC Publication No. 390
Southern
Regional
Aquaculture
Center
June, 1990
Transportation of Warmwater Fish
Equipment and Guidelines
Gary L. Jensen’
Fish transport is often the final
step in production. Most labor
and production costs have already occurred, and any fish loss
from death or injury, at this
stage, severely affects the profit
margin. Most fish losses from
hauling are the result of the activation of latent disease organisms or osmoregulatory
problems. Poor water quality,
overcrowding and improper
tempering cause serious fish losses. The ultimate goal is to provide healthy fish that survive
after stocking.
preferred. Oxygenate well water
thoroughly before it is used in
the transport tank to remove
carbon dioxide and add dissolved
oxygen. Beware of high levels of
ammonia and iron that can occur
in well water. Ammonia can be
removed by aging water in a
tank, and iron can be removed by
aerating water before use.
Pond water is less desirable because it often has a heavy algae
bloom and other organisms that
remove oxygen from the water
and produce ammonia as a waste
product. Pond water also is more
likely to have harmful fish
pathogens than well or spring
water. Clear pond water without
a heavy algae bloom can be used
for short trips. Special care is
Water quality
Water quality is an important
factor to manage while fish are
crowded and stressed in hauling.
The major parameters that limit
the loading density of fish are
adequate oxygen levels and buildup of toxic waste products such
as ammonia and carbon dioxide.
Temperature, pH, loading density and trip duration affect the
severity of these problems.
A suitable water supply is
needed for short-term holding
and hauling. Cool, uncontaminated well water is
Custom designed transport truck using liquid oxygen for aeration. Note size
of discharge opening for large fish and side location of drain.
needed when any surface water
is used to make sure that no
harmful contaminants are
present.
Fish condition
One critical factor to the successful handling and transport of fish
is that fish be healthy and in
good condition before they are
hauled. Another important consideration is the variability of
tolerance to loading and
transport stress among species.
Some species are very hardy
while others require special
precautions. With so many variables important in transporting
fish, it is imperative that the
hauler is knowledgeable about acceptable loading rates for the
specific conditions. Start with a
safe loading rate, and increase
later based on experience and
results.
Hauling tank systems
The hauling unit should be compatible with its intended use. A
light pickup can handle a 100gallon tank while a 3/4 ton pickup can pull a gooseneck trailer
with two 350-gallon tanks.
Water is heavy--one gallon
weighs 8.3 pounds. Some units
are attached to the frames or
flatbed of trucks. Other units are
portable and can be lifted
manually or with a winch and/or
pulleys. Gooseneck trailers with
electric brakes are also used to
carry transport tanks. The pickup truck used to pull the
gooseneck is then available for
other farm work. Specially
designed self-contained transport
vehicles are common in situations where they are used
regularly to haul large quantities
of fish. A producer can save
money by purchasing used equipment in good condition. Follow
recommended gross weight
limits for vehicles and tonnage
weight of the trailer for safety
reasons.
In the South, most hauling tanks
are insulated unless trips are
—. .
Typical long-haul truck delivery system utilizing blowers and oxygen. This
tractor-trailer rig with transport tanks in series can haul large quantities
of fish.
short or tanks are for on-farm
use only. Insulation means little
or no ice is required to maintain
temperatures on long trips.
Urethane foam, plastic foam and
corkboard are common insulating materials used as filler between tank walls.
Tank capacities range from 75
gallons to 2,500 gallons with the
most common tanks holding 100
to 300 gallons. Tank depth is
usually 28 inches to 32 inches.
Most tanks are rectangular and
may have from one to eight compartments with varying arrangements. More than one
compartment is needed if several
fish sizes or species require
transport at the same time.
Large or long tanks must contain
baffles to reduce water sloshing
that can injure fish and create
dangerous driving conditions.
Welds in single, long tanks may
break if the truck bed warps.
This can be avoided if smaller,
standard tanks with the same
carrying capacity are placed side
by side.
Most tanks are made of 3/16-inch
aluminum or l/4-inch thick
fiberglass. Uninsulated
fiberglass or marine plywood
tanks work well for short trips.
Metal tanks are less likely to be
broken or damaged. Any
hardware on the tank should be
aluminum, stainless steel or
other rust-resistant material.
The top doors or lids of the tank
should be large if fish will be
loaded with a boom and fish basket. Large doors make fish
removal easier if dip netting is required.
The tank drain can be located
either in the rear or side of the
tank. Side outlets allow easy unloading of fish to holding vats or
ponds by means of chutes or extended discharge pipes. These
reduce rough handling caused by
dip-netting. The discharge opening should be large enough to
easily pass the largest fish
hauled and should be equipped
with a quick release gate or plug.
Drain openings can be rectangular or round with round drains
usually 3 to 8 inches in diameter.
These may be controlled with inside rubber stoppers, outside expansion plugs or threaded caps.
A sliding inside gate, over the
drain opening, is useful to control the rate of discharge and permit removal of outside cap or
plug without releasing water or
fish.
A sloped false bottom permits
the complete discharge of water
and fish with minimal extra handling. The bottom of the drain
opening should be flush with the
tank bottom. A lip on this drain
prevents total emptying of water
and fish.
Tanks should be equipped with
an overflow drain to maintain
water level and allow agitators
to function at the proper operating depth. Electrical outlet boxes
should be available for easy hookup of agitators. A central junction box with wires leading to
individual outlets works well.
Another feature is an air vent or
scoop to permit air circulation in
the space between the water surface and tank top. Adequate ventilation is important especially
on long trips, to reduce accumulation of carbon dioxide.
Although uncommon in the
South, tanks may have clear, vertical tubes or panels for determining fish weights by calibrated
water displacement rather than
by scale weighing. This method
requires that water transfer with
fish be minimized. It is commonly used in the trout industry
where fish pumps and dewatering towers are used to move fish
from production or holding units
to transport tanks. Handling is
minimal and efficient.
Aeration systems
A variety of methods can aerate
water during hauling. Because
fish are densely crowded and excited--especially after loading--it
is essential to have an aeration
system that provides adequate
dissolved oxygen (DO) rapidly
and efficiently. For most cases,
maintain oxygen concentrations
above 6 parts per million (ppm)
at all times. Higher oxygen
levels, near air saturation, may
lessen the effects of any ammonia buildup, especially on long
trips.
Most hauling units today use
some form of pure oxygen. Most
are equipped with compressed
oxygen tanks but some haulers
use liquid oxygen (LOX) because
it is cheaper, weighs less, and
fewer tanks supply the same
amount of oxygen. A standard
oxygen cylinder holds about 280
cubic feet of oxygen and weighs
about 150 pounds. A LOX dewar
(tank) holds about 4,500 cubic
feet of oxygen and weighs about
780 pounds. Other sizes of
oxygen cylinders also are available. Follow all recommended
safety precautions when near
pure oxygen.
Both kinds of oxygen tanks can
be leased or purchased. A LOX
dewar is more expensive. LOX is
cheaper per cubic foot of oxygen
than compressed oxygen in most
locations. For small fish loads
and short trips, compressed
oxygen is adequate. Consider
cost, needs, service and convenience in deciding which
oxygen source to use. Also, liquid oxygen should not be stored
for long periods because of gas
losses through pressure release
valves at the rate of about 2 percent daily. Compressed oxygen
can be stored indefinitely. Single
stage pressure regulators are
needed for each oxygen tank, and
each aeration line to a tank compartment should have a flow
meter (lpm) to adjust supply
rates.
Various diffusers are used for dispersing oxygen from the bottom
of the tank compartment. Carbon stones or rods, MicroporeTM
tubing, BioweaveTM, PorexTM, and
others work well. Aeration lines
from the regulator to flow meters
and drop lines to the diffusers
are usually 3/8-inch ID flexible
plastic tubing or PVC pipe. Some
diffusers are made of PVC
frames that fit the bottom of the
tank compartment.
Agitators are commonly used
either alone or in combination
with pure oxygen. Agitators can
also provide back-up aeration for
emergency situations. For short
trips agitators alone may suffice
The combination of agitators
with oxygen diffusers works well
for fish hauling. Agitators do not
have good mixing characteristics
alone, and low DO may result in
corners of the hauling tank.
Oxygen diffusers do not remove
carbon dioxide efficiently because of minor agitation at the
water surface, but under the
high density hauling conditions,
they supply oxygen efficiently.
Most agitators are 12-volt direct
current (DC) units powered by
the vehicle’s battery and alternator. Alternators should be
heavy-duty, and the vehicle’s engine should be kept running
during a short stop to keep the
battery charged. One agitator
per compartment is used. Excessive agitation can be harmful to
delicate scaled fish, and diffused
oxygen is preferred for small fish.
Other equipment and
supplies
To assure the successful delivery
of fish, other additional equipment and supplies are recommended. If you sell fish in many
small lots along a route, an easily attached or extendable support for a hanging scale is useful.
The scale should be in pounds
and ounces and have a weighing
bucket. You will need a suitable
dip net to transfer fish.
An oxygen meter or test kit is important for measuring oxygen
concentrations in transport and
receiving waters. Oxygen levels
and water temperature can be
monitored easily by using an
oxygen meter with a long cable
attached to the probe.
Gauges and manifolds that indicate the functional status of
agitators and flow meters can be
put inside the truck cabin. Flow
meters may also be located or
oriented for easy visual inspection to make certain oxygen is
supplied at all times during the
trip.
Water hardness, alkalinity and
pH test kits should be used to
check transport and receiving
waters, especially if fish are
removed from hard, highly
alkaline water to soft, acid water
with low alkalinity. If you deliver
fish to sites where chlorinated
water is used, a chlorine test kit
is helpful. Sodium thiosulfate
may be needed to dechlorinate
water.
material for harvest seines and
dip nets to avoid injuring or gilling fish. Purchase treated nylon
nets or treat with a net coating
for seining catfish. Use soft 3/16inch knotless nylon mesh nets
for delicate minnows.
Polyethylene nets do not require
special treatment.
treated with chlorine in a 10
ppm solution for an hour.
Household bleach (5 percent
chlorine) or HTH (65 percent
chlorine) can be used. Flush
tanks thoroughly after chlorine
treatment. A 5 percent solution
of formalin can also be used to
disinfect.
Carry at least one extra agitator
and other essential spare parts,
like fittings and hoses, at all
times. A 12-volt submergible
pump or gasoline-engine pump is
useful for adding water in an
emergency or for tempering fish
by pumping pond water at the
stocking site into the transport
unit to exchange the water slowly and avoid any shock from
temperature or water quality differences.
After fish are harvested, carefully remove debris and give fish a
resting period of several hours
before they are handled again. If
holding vats are available, you
can easily grade, clean and sort
fish prior to shipment. Then the
fish may be slowly tempered or
acclimated to the expected
transport water temperature.
To avoid untimely delays, get
good directions to your destination. Plan your trip to include
any drop-offs or water refreshening. Be certain that all required
permits or licenses are in order
and carried in the vehicle in case
of an inspection check. Some
states require special markings
on fish transport trucks. Check
with the proper regulatory
authorities for current information on laws and regulations on
transporting and marketing live
fish before doing interstate business.
Pre-hauling handling and
planning
Fish must be in good health and
good condition before they are
loaded into transport units. Fish
in poor condition may die during
transport or suffer delayed death
after stocking. Withhold food
from fish for at least 1 to 2 days
before transport during warmer
months and 3 days or longer
during colder weather. Fish with
empty stomachs are hardier, will
not regurgitate food in the
transport unit and will produce
less metabolic waste. Do not
starve cannibalistic fish such as
striped bass or red drum longer
than 3 days before harvest.
If possible, use V-traps or harvest basins in ponds to harvest
small, delicate, scaled fish. For
larger fish, harvest as many as
possible by seining or trapping
as water level is lowered. Select
the proper mesh size and net
If fish are to be held in ponds,
maintain adequate aeration and
water quality. Secure live cars or
harvesting seines to the pond bottom. Avoid holding large fish or
active species in cages. Do not
overload cages. If fish begin to
die, diagnose the problem, then
treat and return fish to the pond
rather than transport them.
Prophylactic treatment with approved chemicals can reduce
pathogenic organisms that could
cause problems during or after
transport. Paracide-F maybe
used in holding vats for 15minute to l-hour baths. Avoid
overtreating with excessive doses
or combinations of chemicals. Be
prepared to flush any treatment
with fresh water if fish show any
signs of stress.
The transport unit and equipment, such as dip nets, should be
dried and disinfected between
loads of fish. This practice
reduces the possibility of spreading disease pathogens from one
group of fish to another. Tanks
can be thoroughly air-dried or
The following table provides information on matching truck
sizes with fish hauling tanks of
various capacities.
Truck size
Recommended
Tank Capacity
(short ton)
(gallons water)
Tractor-trailer
2.5
1.5
1.0
0.75
0.5
5,000
1,200
600-800
400
300
100
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with
the understanding that no discrimination is
intended and no endorsement by the
Cooperative Extension Service is implied.
Acknowledgment
Special thanks to Gary Carmichael and Joseph Tomasso for providing useful information for this
publication.
This publication was supported in part by a grant from the United States Department of Agriculture, Number 87-CRSR-2-3218, sponsored
jointly by the Cooperative State Research Service and the Extension Service.
SRAC
Publication
No.393
Regional
Aquaculture
Center
June,1990
T
o rW
L
R
F
T
a
S
GaryL. Jensen*
The misconception exists that
“per gallon of water” includes
water displaced by the fish. This
is incorrect. Gallons of water
should be determined before fish
are loaded. The change in water
volume (water displaced) after
fish are added can be measured
to determine the loading rate, as
expressed in pounds per gallon:
12gallonswaterdisplaced
x 2,000 poundsfish= 240gallonswaterdisplaced
100poundsfish
Some fish species, like channel
catfish and certain bait minnews, have been transported for
many years. Government
hatcheries have experience with
transporting other cultured
species and distributing them at
various sizes. Other species such
as redfish, hybrid striped bass
and tilapia are newcomers and
experience with handling and
transporting is more limited. The
Poundsof fish
TankCapacity- Water Displaced
(gallons)
(gallons)
About 8 pounds of fish will displace about 1 gallon of water.
This displacement factor is important for determining the
proper capacity of a hauling unit
or compartment based on anticipated fish load in pounds. For
example, to transport 1,000
pounds of catfish weighing 250
pounds/1,000 at 5 pounds of catfish per gallon, your tank needs
at least 200 gallons based on
loading rate and 125 gallons for
displacement (or 325 gallons). As
an easy guide, 12 gallons of
water are displaced per 100
pounds of fish weight. For example, 2,000 pounds of fish will
displace about 240 gallons of
water as shown in next column.
A typicalpickup haulingtank usedfor haulingall sizes of fingerlingfish
Photoshowsslideon topand quick-openinggates at bottomleft.
in
following guidelines are based on
recommendations from experience and research as a starting point. Higher loading rates
are possible.
Channel catfish
Catfish transport well and are
easier to temper when
transported at 60° F in summer
and 45 to 50°F
winter. If
fingerlings less than 3 inches are
transported above 70° F, extreme
caution is required. A serious
channel catfish virus disease is a
threat to fingerlings at high
temperatures. Hardness and
alkalinity values above 75 ppm
are recommended for transport
water. Salt is beneficial at 0.2 to
1 percent.
Fry 3 to 7 days old can be
transported in double-layered
plastic bags at rates up to 15,000
fry per gallon of water. Fry 7 to
14 days old can be loaded at
7,000 per gallon for an 8-hour
trip at 70° F. Fill the remaining
volume in bag with compressed
pure oxygen, and close tightly to
prevent gas leakage.
Ice in zip-top plastic bags can be
placed next to the container to
maintain temperature below
80° F. Transport the boxes in an
air-conditioned vehicle if possible. Avoid direct outdoor sunlight, and never leave an
uninsulated container inside a
closed vehicle on a hot, sunny
day for more than a few minutes.
Fry transport well for up to 24
hours. On delivery, temper fry by
placing plastic bag in tub of pond
water and wait about 30 minutes
for temperatures to equalize. Do
not place bags in direct sunlight.
On farms, catfish fry are
transported from hatcheries to
ponds in small transport boxes of
50 to 100 gallons. Use diffused
oxygen, not agitators. Do not
overcrowd. If fry crowd to the surface, the fish load is excessive.
Catfish eggs can also be shipped
in plastic bags with water (75° to
80º F) and pure oxygen. Two to
three egg masses per plastic shipping bag work well. Do not ship
eggs that may hatch during transit. To ship in hauling tanks
place egg masses in a soft mesh
bag suspended from a floating
Styrofoam collar. This provides
good water circulation.
Adjustments for other conditions: Increase loading rate by 25
percent for each drop of 10° F
below 65° F or if pure oxygen is
used; decrease loading rate by 25
percent for each increase in 10°F
above 65° F.
Bait minnows
Some species of bait minnows
are more tolerant than others to
handling. Golden shiners are
especially delicate when temperatures are above 60° F and often
suffer delayed mortalities when
suddenly transferred from 60° F
to 75°F water that is common in
retail holding vats during the
summer. Shiners haul well in
salt solutions of less than 0.2
percent.
0
1
0
0
1
1
0
2
1
1
1
Golden shiners can tolerate a
temperature drop of 15°F, but
fathead minnows and bait-sized
goldfish require gradual tempering. Haul goldfish and fathead
minnows in water with the same
temperature as the pond for
short hauls. Goldfish can be
shipped at 1 pound per gallon in
summer and 2 pounds per gallon
in winter. Smaller goldfish
transport well at 1 1/2 pounds
per gallon in winter at 55°F with
LOX supplied at 5 liters per
minute (lpm). Fish should be
held in vats at least 24 hours
prior to transport. Young
goldfish less than 3 inches are
very soft and delicate to handle.
Minnows are successfully hauled
with agitators and pure oxygen
at 1 pound per gallon during
cooler months and 0.7 pounds
per gallon in summer.
4
2
1
1.50
Tropical fish
8
2
2
1
3
2
2
2
5
4
2
5
5
4
6
5
3
4
Bags should have a flat bottom
with four corners. Place the bag
in a cardboard box or ice cooler.
If only occasional plastic bag
shipping is done, you maybe
able to obtain insulated boxes
with shipping bags from local pet
stores that sell ornamental fish.
Broodfish can be transported,
but special care is required
during the spawning season.
Anesthetize broodfish or place
them in burlap bags to prevent
fighting.
Table1. Guidelinesfortransportingcatfish.
TransportTimein Hours
12
Sizeof Fish
8
Poundsper 1,000
Fish
0
2
1
Table 1 provides guidelines for
transporting catfish fingerlings
and food-sized fish. Numbers are
pounds of fish per gallon of water
at 65° F.
16
Tropical fish are usually starved
for 48 hours prior to transporting. Salt and anesthetics are
added to the water, which is
reduced to 77°F. Some species
can tolerate lower temperatures.
Loading rates are 0.4 to 0.7
pounds-per gallon. Water hardness above 100 ppm is preferred.
Tilapia of 9 pounds per 1,000 fish
can be shipped in plastic ‘bags at
up to 5 pounds per gallon at 60°
F for 24 hours.
Striped bass and its
hybrids
Striped bass and its hybrids can
be grown in either fresh or brackish water, but these fish are
very sensitive to handling and
should always be moved in water
whenever possible. Recent
studies indicate that fry 5 to 30
days old are not as sensitive to
netting and light shock as previously believed.
Harvest striped bass when pond
water is cool and not muddy.
Transfer fish immediately to a
container with oxygenated water
and 0.2 to 0.5 percent salt. Provide a rest period of several
hours in 0.1 percent salt if possible, and then haul at the same
salinity. Striped bass require no
tempering from fresh water to
0.1 percent saline water.
Hardness above 75 ppm is
recommended.
Loading rates include 1,000 per
pound fish at 0.15 pounds per
gallon for 10 hours; 5 per pound
fish at 1.5 pounds per gallon for
10 hours or 0.75 pounds per gallon for 15 hours; or 500 per
pound fish at 0.5 pounds per gallon for 24 hours. Optimum water
temperature is 55° to 65°F (70°
to 75° F for adult broodfish) and
salinity of 1 percent.
Striped bass fry at least 5 days
old appear to survive transport
and stocking better than younger
fish. Place 40,000 fry per gallon
in oxygenated plastic bags. For
fry, temper gradually at a rate of
one-half hour per 3° F difference
in temperature. Do not haul fish
smaller that 2 inches in units
with agitators because of possible mechanical injury. Suggested loading rates for 2-inch
striped bass include 0.5 pounds
per gallon for 1 to 4 hours, 0.33
pounds per gallon for 4 to 8
hours and 0.25 pounds per gallon
for more than 8 hours.
Largemouth bass
Harvest bass after 2 days
without food, by seining or with
glass V-traps before the water
level is drawn down and water
becomes muddy. Provide a resting period after harvest and
before loading. Salt is used up to
0.5 percent. Pure oxygen is
preferable, and DO should be 7
ppm for short trips and 10 ppm
on trips longer than 8 hours.
Bass may require up to 3 days to
recover from hauling stress.
Bass sac-fry 1 to 3 days old can
be shipped for 3 to 4 days in plastic bags at 11,400 fish per gallon.
Square-bottomed bags are
preferable. Water should be overlaid with pure oxygen (Figure 1).
Table 2 provides recommended
loading densities for largemouth
bass for trips less than 30 hours.
Table2. Loadingdensitiesfor
Iargemouthbass.
FishSize
LoadingRate
(inches)
(pounds/gallon)
5
1.5
4
1.0
3
0.66
2
0.50
1
0.33
Recent studies with transporting
bass indicate the usefulness of
prophylactic disease treatment.
Starve fish 3 days before loading.
Sedate fish with MS-222 at 50
ppm before crowding and loading. Haul fish in 60° F water
with a hardness and an
alkalinity of at least 150 ppm
with MS-222 at 25 ppm.
Bluegill
Figure 1. These are typicalplastic bags and styrofoamboxes used for
transportingsmallfish. Watertemperaturemustbeadjustedbeforeadding
added fish, and .
be
oxygen
beforetransporting.
Table 3 provides guidelines for
transporting bluegill at temperatures between 65° and 80° F and
up to 16 hours. Bluegill are normally hauled with 0.3 to 0.5 percent salt.
Table3. Guidelinesfor
transportingbluegill.
LoadingRate
FishSize
(inches)
(pounds/gallon)
4
1.00
0.66
3
2
0.50
0.33
1
Red drum (redfish)
Information on this species is
scarce, but practices similar to
those for striped bass should be
a good guide. Haul red drum in
water about 70° F. Do not haul in
fresh water. Transport in full
strength seawater when stocking
fish into water near 30 ppt
salinity. If fish will be stocked
into fresh water, use 10 percent
saline water and dilute slowly
with fresh water for 1 to 4 hours
before unloading. Acclimate fish
at least 5 hours if fish are moved
from water of about 10 ppt
salinity to fresh water.
Loading rates for 1-to 2-inch fish
include 0.33 pounds per gallon
for less than 8 hours and 0.25
pounds per gallon for longer
trips. One-inch fish have also
been transported at 0.1 pounds
per gallon at 80° F in 32 ppt
salinity for 5 hours. Fingerlings
5 to 8 inches long transport well
in salinities from 4 ppt to 32 ppt.
More information is needed on
optimum hauling temperatures
and salinities for different sizes
of red drum at various loading
densities. Acclimation rates for.
different conditions also need
further evaluation.
Pickup and tank equipped with
oxygenusedfor fingerlingdelivery.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with
the understanding that no discrimination
is intended and no endorsement by the
Cooperative Extension Service is implied.
This publication was supported in part by a grant from the United States Department of Agriculture, Number
jointly by the Cooperative State Research Service and the Extension Service.
87-CRSR-2-3218,
sponsored
SRAC Publication No. 3900
PR
November 2004
VI
Anesthetics in Aquaculture
Shawn D. Coyle, Robert M. Durborow and James H. Tidwell*
Fish are easily stressed by handling and transport and stress can
result in immuno-suppression,
physical injury, or even death. In
aquaculture, anesthetics are used
during transportation to prevent
physical injury and reduce metabolism (DO consumption and excretion). They are also used to immobilize fish so they can be handled
more easily during harvesting,
sampling and spawning procedures.
An ideal anesthetic should induce
anesthesia rapidly with minimum
hyperactivity or stress. It should
be easy to administer and should
maintain the animal in the chosen
state. When the animal is removed
from the anesthetic, recovery
should be rapid. The anesthetic
should be effective at low doses
and the toxic dose should greatly
exceed the effective dose so that
there is a wide margin of safety.
(Table 1). The stage achieved usually depends on the dose and the
length of exposure. When an anesthetic is first administered (induction) fish may become hyperactive
for a few seconds.
The condition of the animals must
be visually monitored during this
maintenance period. A change in
breathing rate is the most obvious
indicator of over-exposure. If this
occurs, animals must be moved or
the systems flushed immediately.
Maintenance
Once the desired degree of anesthesia is reached, it may be desirable to maintain fish in that state
for some time. Because drug dose
and exposure time are often
cumulative, it is difficult to maintain a uniform depth of anesthesia. One reason for this is that levels of anesthetic may continue to
accumulate in the brain and muscle even after blood levels have
attained equilibrium. A desired
level of anesthesia can usually be
maintained by reducing the
dosage.
Recovery
During the recovery stage the anesthetic is withdrawn and fish return
to a normal state. To reduce recovery time, induction should be rapid
and handling time should be minimal. Initial recovery may take from
a few seconds to several minutes,
depending on the anesthetic administered. Typically, the animal will
attempt to right itself and will begin
to respond to noise and other sensory stimuli. Full recovery can take
minutes to hours, depending on the
species and drug used.
Table 1. Stages of anesthesia in fish.
Stages of anesthesia
Stage
Condition
Behavior/Response
Induction
I
Sedation
Motion & breathing reduced
Most anesthetics can produce several levels or stages of anesthesia.
Stages include sedation, anesthesia, surgical anesthesia and death
II
Anesthesia
Partial loss of equilibrium
Reactive to touch stimuli
III
Surgical anesthesia
Total loss of equilibrium
No reaction to touch stimuli
IV
Death
Breathing & heart beat stop
Overdose - eventual death
*Kentucky State University Aquaculture
Research Center.
Great care should be taken during
the recovery stage to minimize
stress and prevent mortality. If an
animal fails to recover, increasing
the flow of anesthetic-free water
over the gills will often accelerate
and normalize the heart beat.
Move the fish backwards and forwards in the recovery bath or gently pass water over the gills with a
hose. This increases gill blood
flow and eliminates the drug more
rapidly.
Legal aspects
Many chemical anesthetics have
been used on fish over the years.
Most have now been discarded or
are not widely used. The U.S. Food
and Drug Administration (FDA)
regulates which chemicals can be
used on food fish. When fish are
exposed to an anesthetic, residues
or metabolites of the substance
remain in the flesh for a period of
time until they are excreted or
metabolized. Therefore, FDA may
require a specific withdrawal time
before the animal can be used for
food or released into the environment where it might be captured
for food.
Anesthetics are licensed for use in
food animals only after completing a full drug development program designed to protect the cultured animals, human users, the
food chain, and the environment.
The program requires a wide
range of inputs from the drug
company, research scientists,
national agencies, and the farming
and feed industries. Licensing a
new drug is time consuming and
costly. Aquaculture is an important industry worldwide, but it is
still relatively small compared to
other animal production industries and the human medical
industry. For this reason, drug
companies have not been able to
justify the costs of licensing new
drugs because the expected financial return is low. The only anesthetic drug currently approved by
the FDA for use on food fish is tricaine methanesulfonate (MS-222).
Factors affecting
anesthesia
Many factors affect the efficacy of
anesthetics in fish. These can be
divided into biological and environmental factors.
Often, the rate at which anesthetic
drugs become effective is related to
the gill area to body weight ratio,
which can vary considerably
among fish species. Aquatic species
also have different metabolic rates
that affect the rate at which chemicals are absorbed and anesthesia is
induced. For example, cold-water
species seem to respond to lower
concentrations of anesthetic than
warm-water species.
There are also factors that can
affect anesthesia within a particular species. Larger individuals
generally require a greater concentration of anesthetic than smaller
individuals. In contrast, it has also
been reported that the larger,
more active fish in a group are
anesthetized faster than smaller
ones. Many drugs such as MS-222
and benzocaine are fat-soluble;
therefore, in larger fish or gravid
females, anesthesia may last
longer and recovery may be slower as the drug is removed from
the lipid reserves. Also, diseased
or weakened animals are much
more susceptible to anesthetic
treatment.
Environmental factors can also
profoundly affect the efficacy of
certain anesthetics. Aquatic invertebrates and fish are ectotherms;
their body temperature closely follows that of their environment. As
a result, physicochemical passage
of the drug into the fish is also
temperature related. At lower
water temperatures, higher doses
or longer exposure times are
required with MS-222, benzocaine
and 2-phenoxyethanol, presumably because the absorption rate
decreases at lower temperatures.
The pH of an anesthetic solution
also can influence its efficacy, possibly by affecting the ratio of
charged to uncharged molecules.
This is most pronounced with
quinaldine, which loses its efficacy
in solutions with low pH.
Anesthesia of fish
Fish are usually anesthetized by
immersing them in an anesthetic
bath containing a suitable concentration of drug so that the drug is
absorbed through the gills and
rapidly enters the blood stream.
The simplest procedure is to prepare the required drug concentration in an aerated container and
quickly but gently transfer the fish
to the container. The anesthetic
bath and recovery tank should use
water (at a similar temperature
and chemistry) from which the
animals originated. Water quality
needs to be carefully controlled,
especially where large numbers of
animals are being handled and
baths are being reused. Main concerns involve maintaining proper
temperature, adequate dissolved
oxygen, low ammonia and a minimum amount of fecal matter.
Applying an anesthetic solution to
the gills with a spray bottle can be
useful with large animals or if
immersion is impractical. A 100to 200-mg/L solution of MS-222 is
reported to be effective when
applied to the gills of salmonid
broodstock. This method allows
the fish to be handled without
immersion, and it has no effect on
subsequent egg hatching success.
Anesthesia of
aquatic invertebrates
Less is known about anesthetizing
invertebrates because it is not
done as often. Most operations in
crustacean culture can be conducted without anesthesia, although
the rapid movement of shrimp
can present handling problems
and their cannibalistic nature can
be a problem during holding and
transporting. Consequently, there
has been some interest in investigating crustacean anesthetics, particularly for transport. Crustaceans
respond differently to anesthesia
than finfish, possibly because
their synaptic receptor sites are
not affected by certain anesthetics.
For example, MS-222 is not effective on many crustaceans. It seems
that much higher concentrations
are required to anesthetize crus-
taceans than fish. Aqui-S has
been reported to be effective on
freshwater prawns (Macrobrachium
rosenbergii), but only at concentrations 5 to 10 times higher (100 to
200 mg/L) than those used on finfish (20 mg/L). Carbon dioxide is
an effective anesthetic for most
crustaceans. It is most frequently
dispensed as a mixture of baking
soda and acetic acid. Cooling is
also an effective way to immobilize crustaceans, but one must be
careful because cooling can kill the
animals.
Anesthetics used in fish
At this time, only MS-222 is registered for use on food fish in the
U. S. However, many compounds
have been evaluated experimentally and some are being used on
nonfood fish and in research. The
substances described below have
been extensively evaluated in the
U. S. or other countries. Effective
dosages of these drugs for different fish species are summarized in
Table 2.
MS-222
The chemical name for MS-222 is
tricaine methanesulfonate. It is sold
as Tricaine-S and Finquel. It
comes as a white, crystalline powder that can be dissolved in water
at up to an 11% solution. It lowers
the pH of water, creating an acidic
condition that can irritate fish and
cause harmful side effects. To prevent problems, the stock solution
can be buffered with sodium bicarbonate (baking soda) to achieve a
pH of 7. One of the major drawbacks of MS-222 is that even when
fish are deeply anesthetized, handling still increases levels of plasma
cortisol concentrations, an indicator
of stress.
Induction is rapid and can take as
little as 15 seconds. Salmonids are
quickly anesthetized when
immersed in 25 to 50 mg/L.
Anesthesia can be maintained at
10 mg/L. Channel catfish
(Ictalurus punctatus) require 25 to
50 mg/L for sedation and 100 to
250 mg/L for full anesthesia, with
a 3-minute induction time. Up to
100 mg/L is required for some
species, including tilapia.
Generally, concentrations greater
than 100 mg/L should not be
used for salmonids, and levels
higher than 250 mg/L should not
be used for warm-water fish.
Recovery is usually rapid and
equilibrium can be expected to
return after only a few minutes. A
recovery time longer than 10 minutes suggests that too much anesthetic is being used or that the
exposure time is too long. MS-222
has a good safety margin in fish.
In trout, for example, the effective
concentration is 40 mg/L and the
maximum safe concentration is
63 mg/L. The safety margin narrows as temperature rises and
appears to be smaller for smaller
fish. The drug is more potent in
warm waters with low hardness.
MS-222 is excreted in fish urine
within 24 hours and tissue levels
decline to near zero in the same
amount of time. It is approved for
use on food fish in the U. S. and
the United Kingdom, but was
recently banned in Canada. The
withdrawal time for MS-222
required by FDA is 21 days, which
makes it impractical as an anesthetic for fish en route to market.
Benzocaine
Benzocaine, or ethyl aminobenzoate, is a white crystal that is
chemically similar to MS-222.
However, benzocaine is almost
totally insoluble in water and must
first be dissolved in ethanol or acetone. The standard approach is to
prepare a stock solution in ethanol
or acetone (usually 100 g/L) that
will keep for more than a year
when sealed in a dark bottle. In
solution, benzocaine is neutral (pH
7) and therefore causes less hyperactivity and initial stress reaction
than unbuffered MS-222. Benzocaine is effective at approximately
the same doses as tricaine (25 to
100 mg/L). Benzocaine has a fair
margin of safety, although this
appears to be reduced at higher
temperatures. It is not safe for
exposures longer than 15 minutes.
Its efficacy is not affected by water
hardness or pH. As with MS-222, it
is fat-soluble and recovery times
can be prolonged in older fish or
gravid females. Benzocaine is not
approved by FDA for use on food
fish in the U. S.
Quinaldine
Quinaldine is a yellowish, oily liquid with limited water solubility
that must be dissolved in acetone
or alcohol before it is mixed with
water. While it is an effective
anesthetic, it is an irritant to fish,
has an unpleasant odor, and is a
carcinogen. The low cost of
quinaldine has made it a popular
tool for collecting tropical fish for
the aquarium trade, as well as in
the bait and sport fish industries.
Quinaldine sulfonate is a pale yellow, water-soluble powder; it is
more costly than quinaldine or
MS-222.
Quinaldine solutions are acidic
and are usually buffered with
sodium bicarbonate. Induction
takes 1 to 4 minutes and may
cause mild muscle contractions.
Recovery is usually rapid. The
effective treatment concentration
of quinaldine solutions varies
with species, but is generally 15 to
60 mg/L. Grass carp (ctenopharyngodon idella) lose equilibrium within 5 minutes of exposure
to 15 mg/L. However, quinaldine
concentrations of 50 to 1,000
mg/L were required to completely anesthetize tilapia.
Quinaldine may not produce the
deep anesthesia needed for
surgery because some reflex
responsiveness is usually retained.
Higher doses (150 mg/L) have
been used for surgical procedures, but quinaldine is not usually recommended for these procedures. Fish under full quinaldine
anesthesia normally do not stop
their gill ventilation so are not as
susceptible to asphyxia from respiratory arrest as they are with
MS-222. In general, the potency of
quinaldine is higher in hard water
and warm water. Quinaldine is
not approved by the FDA for use
on food fish in the U. S.
2-Phenoxyethanol
2-Phenoxyethanol is an opaque,
oily liquid. This drug is moderately soluble in water but freely soluble in ethanol. The solution is bactericidal and fungicidal and is,
therefore, useful during surgery. It
is relatively inexpensive and
remains active in the diluted state
for at least 3 days. 2-Phenoxyethanol has a relatively large margin
of safety and has been reported to
produce a range of effects from
light sedation to surgical anesthesia at concentrations of 100 to
600 mg/L. Concentrations of 300
to 400 mg/L are useful for short
procedures, and lower concentrations of 100 to 200 mg/L are considered safe for prolonged sedation, such as during transport.
2-Phenoxyethanol is not approved
by FDA for use on food fish in the
U. S.
Metomidate
Metomidate has been used extensively in human medicine. It anesthetizes fish without the usual
stress of an elevated heart rate.
Induction is rapid—1 to 2 minutes—and recovery is faster than
with MS-222. It anesthetizes
salmonids at doses of only 2 to
6 mg/L; low doses are also effective in catfish. In salmonids, metomidate is reported to be more
potent in larger, sea-water- adapted fish than in freshwater fingerlings or parr. With larval goldfish,
Carassius auratus, and red drum,
Sciaenops ocellatus, it has been
reported to produce inadequate
anesthesia with high mortalities.
Metomidate is not approved in
the U. S. for use on food fish and
is not widely used.
Clove oil
Clove oil has been widely used as
an anesthetic in human dentistry
and as a food flavoring. The major
constituent (70 to 90 percent by
weight) is the oil eugenol, but
clove oil contains a wide range of
other compounds that impart its
characteristic odor and flavor. It is
an effective anesthesia in carp
(Cyprinus carpio) at 40 to 120
mg/L. In rainbow trout,
Oncorhynchus mykiss, doses as low
as 2 to 5 mg/L produced sedation
sufficient to transport the fish,
while doses of 40 to 60 mg/L for
3 to 6 minutes gave effective surgical anesthesia. Recovery time
increases with higher doses and
longer exposure time. Clove oil is
also an effective anesthetic for
crustaceans at doses of 100 to
200 mg/L. Clove oil has a very
high margin of safety; however, it
also requires a relatively long
recovery time compared to
MS-222. The major advantage of
clove oil is that it is inexpensive
and not unpleasant to work with.
Clove oil is not approved for use
on food fish in the U. S.
Aqui-S
Aqui-S is a relatively new anesthetic for fish developed by the
Seafood Research Laboratory in
New Zealand. This compound is
approximately 50 percent
isoeugenol and 50 percent
polysorbate 80. A dosage of 20
mg/L is effective for most fish
species and induction is described
as “stress free” because the substance suppresses cortisol. A
recent study indicated that
Aqui-S was an effective anesthetic on freshwater prawns, but only
at much higher concentrations of
100 to 200 mg/L (S. Coyle and J.
Tidwell, unpublished data).
Currently, Aqui-S is approved
for use on food fish in Australia
and New Zealand, with no withdrawal period. It is undergoing
the New Animal Drug Approval
process for use in the U. S., with
no withdrawal time. It is used primarily for the “rested harvest” of
commercial fish species, where the
low stress induction improves the
color, texture and appearance of
the product. If approved for use in
the U. S. with the zero withdrawal
time, Aqui-S would be a valuable tool to use when transporting
live food fish to market.
Carbon dioxide
Carbon dioxide, CO2, has been
used as an anesthetic for many
years, especially during transport.
It is extremely soluble in water
and can simply be diffused into
the water as CO2 gas. However, it
is somewhat difficult to control
the final concentration of CO2.
Carbon dioxide anesthesia is
effective in rainbow trout at 120 to
150 mg/L for fingerlings and 200
to 250 mg/L for adults. Hyperactivity and subsequent stress can
be reduced by buffering the water
with sodium bicarbonate. Sodium
bicarbonate (NaHCO3) and acetic
acid have also been used to produce CO2. When dissolved in
water, sodium bicarbonate releases carbon dioxide if the pH is
acidic. Peak (1998) compared the
efficacy of sodium bicarbonate
and acetic acid to produce anesthesia in smallmouth bass
(Micropterus dolomieu), northern
pike (Esox lucius), and lake stugeon (Acipencer fulvescens). He
found that for these cool-water
species a 2.6-g/L NaHCO3 solution (30 L water, 80 g NaHCO3,
and 80 mL acetic acid) performed
better than the 1.3-g/L NaHCO3
solution (30 L water, 40 g
NaHCO3, and 15 mL acetic acid)
previously recommended for
salmonids. Durborow and Mayer
(unpublished data) found that
largemouth bass (Micropterus
salmoides) reached stage 2 anesthesia after 6 minutes when exposed
to a 0.67-g/L NaHCO3 solution
(30 L water, 20 g NaHCO3, and
7.5 mL acetic acid) at 6 °C, and
recovered in 10 to 15 minutes
after being anesthetized for 1
hour.
The inconvenience of adjusting
and maintaining the required pH
makes other methods more attractive for most procedures. Carbon
dioxide requires a relatively long
induction time—generally 5 minutes at concentrations of 120 to
640 mg/L. The main advantage of
carbon dioxide is that it is not a
controlled substance in the U. S.
and is recognized as a “Low
Regulatory Priority,” unapproved
drug by the FDA. This permits its
use in food fish with no withdrawal time. At this time it is the
only chemical method available
for harvesting or transporting
food fish to market.
Table 2. Dose rates of major anesthetic drugs, evaluated experimentally, for a number of commonly cultured
fish species.
Anesthetic
Atlantic
salmon
Salmo salar
Rainbow trout
Onchorhychus
mykiss
Common carp
Cyprinus carpio
Channel catfish
Ictalurus
punctatus
Nile tilapia
Oreochromis
niloticus
Striped bass
Morone
saxatilis
MS-222
40-50 mg/L
40-60 mg/L
100-250 mg/L
50-250 mg/L
100-200 mg/L
100-150 mg/L
Benzocaine
40 mg/L
25-50 mg/L
ND
ND
25-100 mg/L
50-100 mg/L
Quinaldine
25-40 mg/L
ND
10-40 mg/L
25-60 mg/L
25-50 mg/L
25-40 mg/L
100-200 mg/L
400-600 mg/L
ND
400-600 mg/L
ND
2-Phenoxyethanol 100-200 mg/L
Metomidate
2-10 mg/L
5-6 mg/L
ND
4-8 mg/L
ND
7-10 mg/L
Clove oil
10-50 mg/L
40-120 mg/L
40-100 mg/L
100 mg/L
ND
60 mg/L
Aqui-S
10-50 mg/L
20 mg/L
ND
20-60 mg/L
ND
ND
ND = not determined. Only MS-222 is approved in the U.S. at the time of this publication.
Non-chemical methods
Hypothermia
Lowering water temperature will
tranquilize or immobilize fish.
Lower water temperatures also
increase the oxygen-carrying
capacity of water and reduce the
activity and oxygen consumption
of fish. Water can be cooled by
refrigeration or by adding ice.
Gradual cooling is recommended
because rapid chilling can produce thermal shock. This technique has been used primarily for
transportation. Adult Atlantic
salmon (Salmo salar) can be hauled
long distances when cooled to 0
°C. Carp previously acclimated to
23 °C can be safely maintained in
a state of apparent anesthesia for
5 hours at 4 °C, although lower
temperatures cause mortality.
Hypothermia is commonly used
on crustaceans during transportation. Market-size freshwater
prawns can be transported at high
densities (100 to 200 g/L) if water
temperature is cooled to 16 to 18
°C (S. Coyle and J. Tidwell,
unpublished data).
When fish are immobilized by
lowering water temperature, the
safety margin is frequently quite
small and deaths occur if the temperature is lowered too far or too
quickly. Thus, the rate of cooling
should be controlled carefully and
the required temperature should
be maintained. As a rule of
thumb, the water temperature
should not be reduced more than
1 °C every 15 minutes. Hypothermia is often used in combination with chemical anesthesia to
reduce the amount of anesthetic
required, reduce oxygen consumption, and increase the
amount of time the fish are anesthetized.
Electro-anesthesia
Another alternative to chemical
anesthesia is the use of electricity.
Alternating current (AC) and
square waves in the form of
chopped direct current (DC) have
been used in electro-fishing for
many years. Electro-anesthesia is
not effective in seawater because
seawater is more conductive than
fish. In freshwater, the fish are
more conductive than the water
and the easiest route for electrons
is through the fish.
Fish subjected to low-voltage DC
become immobile; however, this is
effective only while the fish are in
the electrical field. If the current
stops, the fish will escape almost
immediately. This procedure only
immobilizes and does not produce
true anesthesia.
AC current produces a short-term
anesthesia and turning off the
supply does not negate the effects.
Larger fish are affected more
rapidly than smaller ones; the
length of time fish remain in the
anesthetized state increases with
body length. At 110 to 115 volts,
anesthesia was shown to last for
less than 1 minute; higher voltages (220 to 240) are preferable
and can produce loss of reactivity
to touch stimuli for up to 5 minutes.
Electrical stimulation produces
violent muscular responses that
can disfigure or kill. The safety of
the animal and the operator are
the greatest concern when using
electricity. Electricity is unsafe to
use around water; therefore, electro-anesthesia poses special problems. Multiple electrical safety
features and strict codes of operation are required to approach a
sufficient degree of safety.
Transportation and
anesthesia
The stress caused by handling,
grading and transporting can be
considerable. It may be preferable
to anesthetize fish as they are
loaded for transport and/or to
add ice to the water in transport
tanks to reduce metabolic activity.
Sedation can be beneficial in the
bulk transportation of fish stocks,
especially over long distances and
when fish density is high. The
major concerns in transporting
aquatic animals are the management of handling stress, mechanical shock, heat stress, and water
quality.
Fish should not be sedated too
deeply or they will sink to the bottom of the hauling tank where
very high densities can cause
rapid water quality deterioration
and suffocation. As previously
stated, there are no chemical anesthetics (other than CO2) approved
for use on food fish in the U. S.
with zero withdrawal time.
Therefore, carbon dioxide and
hypothermia are the only legal
means of sedation for transporting
live food fish to market.
Conclusion
Anesthetics are chemical or physical agents that calm animals and
cause them to progressively lose
their mobility, equilibrium, consciousness, and finally their reflex
action. In fisheries and aquaculture, anesthetics are helpful for
reducing the stress caused by handling and transport. Many factors
can affect the efficacy of anesthetic
treatments; therefore, experimental dosages should be tested on a
small group of non-critical animals before any large-scale anesthetizing is done.
For environmental and human
safety, the production, sale and
use of chemicals is regulated by
government agencies. In the U. S.,
FDA regulates the use of chemicals on food fish. Currently, the
only chemical anesthetic
approved by the FDA for use on
food fish is MS-222; it requires a
21-day withdrawal period. These
regulations are subject to change,
and users are encouraged to check
with local Extension specialists
regularly for new information.
Suggested Reading
Peak, S. 1980. Sodium bicarbonate
and clove oil as potential
anesthetics for nonsalmonid
fishes. North American Journal
of Fisheries Management 18(4):
919-924.
Piper, R. G., I. B. McElwain, L. E.
Orme, J. P. McCraren, L. G.
Fowler and J. Leonard. 1982.
Fish Hatchery Management.
U.S. Fish and Wildlife Service,
Washington, D.C.
Marking, L. L. and F. P. Meyer.
1985. Are better anesthetics
needed in fisheries? Fisheries
10(6): 2-5.
Ross, L. G. and B. Ross. 1999.
Anaesthetic and Sedative
Techniques for Aquatic
Animals. Blackwell Science,
Inc., Malden, MA.159 pp.
Dupree, H. K. and J. V. Huner.
1984. Third report to the fish
farmers: The status of
warmwater fish farming and
progress in fish farming
research. U.S. Fish and
Wildlife Service, Washington,
D.C.
SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering
Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not
been revised are considered to reflect the current state of knowledge.
The work reported in this publication was supported in part by the Southern Regional Aquaculture Center
through Grant No. 2002-38500-11085 from the United States Department of Agriculture, Cooperative State
Research, Education, and Extension Service.