UW Policy for the Euthanasia of Fish Species - 2008
Approved July 18, 2002; Minor Revisions July 2, 2008
Small fish species (2-6cm in length) typically utilized in laboratory research include zebrafish, medaka, fathead minnow, goldfish, swordtail, and platyfish among others. Large fish species (>6cm in length) typically used include salmon, trout, tilapia, catfish, hybrid-striped bass, bass, bluegill, sturgeon and others.
Chemical agents such as tricaine methanesulfonate (MS-222 or TMS) or
benzocaine hydrochloride (ethyl aminobenzoate), should be used as the method of choice for the euthanasia
all fish species. The
dosage required for euthanasia with either of these compounds is higher than the anesthetic dose, but varies
greatly with species, size, and water temperature. In addition, a longer time of exposure to the chemical
agent (relative to anesthesia) is required to ensure that death occurs. Fish should be removed only after
ten minutes have passed since their last observed opercular movements (respiration) have occurred.
A. Primary euthanasia methods for fish (methods that can be used alone) include:
- MS-222/TMS- dosage: 50 to 250 mg/L
[buffered to a neutral pH with sodium
Note: Fish euthanized with MS-222 cannot be used for human consumption.
- Benzocaine-dosage: 50 to 500 mg/L
a neutral pH with sodium bicarbonate (NaHCO3)]
Note: Fish euthanized with Benzocaine cannot be used for human consumption.
- Exposure to a solution saturated
with carbon dioxide (CO2):
When possible, carbon dioxide should be used from a compressed gas cylinder source. However,
the AVMA Guidelines on Euthanasia (2) does not address the issue of the source/production of carbon dioxide
as it relates to aquatic animal species. The use of chemical methods for the production of carbon dioxide,
such as a saturated solution of sodium bicarbonate or Alka-Seltzer ®, has been proven quite effective
with fish as noted in the literature. When dosed adequately sodium bicarbonate renders rapid loss of consciousness
and death (3,5). As
a result, the use of carbon dioxide liberated by chemical means will also be acceptable for the euthanasia of
fish when compressed carbon dioxide gas cylinders cannot be used. Individuals who have demonstrated competency
with this technique to qualified personnel (i.e. aquatic animal veterinarian or his/her designate) should only
perform the euthanasia of fish by carbon dioxide.
Sodium bicarbonate dosage: (30g/L or 120g/gallon)
Alka-Seltzer ® dosage: (1 tablet/ 20L or 2 tablets/ 10gallons)
Note: Fish euthanized with sodium bicarbonate or Alka-Seltzer® should not be used for human consumption.
Protocol: Fish should be placed into a container with an appropriate volume of water that will provide
free movement of fish to be euthanized. Water should then be saturated with carbon dioxide from either a compressed
gas cylinder (via the use of an air stone with a moderate flow rate for ~5-10 minutes) or by dissolving enough
sodium bicarbonate or Alka-Seltzer® into the water (via the dosages previously provided). Fish should be
removed only after ten minutes have passed since their last observed opercular movements (respiration) have
- Chilling of Tropical species- The AVMA Guidelines on Euthanasia (2) concludes that cooling to 4°C will
decrease metabolism and facilitate handling of poikilothermic species. This method by itself should only be
used to facilitate handling, and it does not constitute an acceptable method of euthanasia since there is
no evidence that it reduces pain or is clinically efficacious. However, the guidelines do not discuss chilling
to 4°C as a method for euthanasia for tropical species. Because tropical fish species, (i.e. zebrafish,
medaka, and platyfish), have minimal to no physiologic adaptation mechanism for adjusting to cold (4°C)
water, cooling to 4°C should be considered an acceptable method of euthanasia since the rapid decrease
in temperature from 26°C (or higher) to 4°C induces rapid loss of consciousness and is lethal to these
species. Fish euthanized by this method should not come in direct contact with the ice, because this may cause
thermal burns and induce pain, but rather the ice should be added to a lowered amount of water for a contact
time of 20 minutes.
Protocol: In a container of an appropriate size for the number and size of fish to
be euthanized, place a small volume of water that will still allow the fish to freely move about. To this
volume of water add four times the volume of ice such that there is a 1:4 ratio of water to ice. Allow the fish to remain in ice-water
bath for 20 minutes prior to removing. Afterwards, transfer the fish to the freezer for storage prior
B. Secondary euthanasia methods for fish (methods that cannot be used alone and must be followed
by an adjunct method to ensure death):
- Sharp blow to the head- This method must be followed by exsanguination (via severing the
large branchial vessels or large caudal tail vessels) or decapitation (via the use of a sharp blade).
or Direct electrical current- This method must be followed by exsanguination (via severing the large
branchial vessels or large caudal tail vessels) or decapitation (via the use of a sharp blade). [Note: the
use of electrical current (electrofishing) must follow the protocol/guidelines provided by the Marine Resources
Division of the Washington State Department of Fish and Wildlife.]
- Chilling of Non-tropical species in salt
water - Since non-tropical species have adaptive mechanisms to handle decreased temperature ranges, the use
of chilling to 4°C (without direct contact of the fish to
the ice) must be followed by decapitation. However, if non-tropical species are exposed to chilled salt
water (-10°C) or fresh water at a temperature significantly less than 4°C (i.e. 0°C) decapitation
is not necessary 10 minutes after the observed cessation of opercular movements.
Euthanasia Policy References:
- Canadian Council on Animal Care, Guide Vol. 1 (2nd Ed.). 1993. Chapter XII – Euthanasia.
- AVMA Guidelines on Euthanasia, June 2007.
M.K. 1993. Fish Medicine. W.B. Saunders Co. Philadelphia.
- The Guide for the Care and Use of Laboratory Animals.
1996. National Academy Press, Washington, D.C.
- Noga, E.J. 1996. Fish Diseases: Diagnosis and Treatment.
Mosby-YearBook, Inc, St. Louis.
- Casebolt, D.B., D.J. Speare, and B.S. Horney. 1998 Care and Use of Fish as
Laboratory Animals: Current State of Knowledge. Lab Animal Science 48(2): 124-136.
- Burns R, McMahan B. Euthanasia
methods for ectothermic vertebrates. In: Bonagura JD, ed.
Continuing veterinary therapy XII. Philadelphia:
WB Saunders Co. 1995:1379-1381.
- Guidelines for the Use of Fishes in Research. 2004. American Fisheries Society
- Guidelines for Use of Fishes in Field Research. In: Fisheries, Vol. 13, No. 2, p. 16-23, 1988 or http://18.104.22.168/pubs/fishguide.html
- Electrofishing Boat
Operation and Maintenance Policy. 1996. Marine Resources Division of the Washington State Department of Fish
- Electrofishing Guidelines for Stream Typing. 1996. Marine Resources Division of the Washington
State Department of Fish and Wildlife.
- USFW 241 FW 6, Electrofishing Guidelines. 1992. http://policy.fws.gov/241fw6.html
- Kolz, A.L., A. Temple, and D. Lam. 1998. Principles and Techniques of Electrofishing. U.S. Fish and
Wildlife Service National Conservation Training Session.