Sodium pentobarbital (60-100 mg/kg) can be
administered intravenously, intra-abdominally or intrapleuroperitoneally
in most ectothermic animals.
Subcutaneous lymph spaces may be used for
administration in frogs and toads.
Time to effect is variable (up to 30 minutes).
Tricaine methane sulfonate (TMS, MS-222)
This chemical may be placed in water for euthanasia
of fish and amphibians.
A concentration of at least 250 mg/L is
recommended. The animal should be left in the solution for at least 10
minutes following cessation of respiratory movements. After removal from
the MS222 solution opening of the body cavity and removal of the heart
may be used to ensure death.
MS 222 is acidic and in concentrations of 500 mg/L
or higher should be buffered with sodium bicarbonate to saturation (pH
7.0 - 7.5).
There is a 21-day withdrawal time for MS 222 in the
US. It should not be used for animals intended for food.
Benzocaine hydrochloride
This chemical may be placed in water for euthanasia
of fish or amphibians.
A concentration of at least 250 mg/L should be
used. Animals should be left in the solution for at least 10 minutes
following cessation of respiratory movement.
Benzocaine (not the hydrochloride) is not water
soluble and is not recommended.
Inhalant agents
Many reptiles and amphibians, including chelonians,
can hold their breath and survive long periods without oxygen. Because
of this, the use of inhalant anesthetics for euthanasia is not
recommended for these species.
Lizards, snakes and fish do not hold their breath
and can be euthanized using inhalant agents.
CO2
Acceptable for amphibians, reptiles and fish.
Loss of consciousness develops rapidly, but
exposure times required for euthanasia are prolonged.
CO2 is more effective in active species and those
with less tendency to hold their breath.
Cooling
There is no evidence that whole body cooling
reduces pain or is clinically efficacious when used as an adjunct to
physical methods of euthanasia in ectothermic animals.
Immobilization of reptiles by cooling is considered
inappropriate and inhumane even if combined with other methods of
euthanasia.
Freezing of unanesthetized animals is not
acceptable as a method of euthanasia.
Rapid freezing (in liquid nitrogen) of deeply
anesthetized animals is acceptable.
