Without trying to put to much of a damper on your plans,
just bear in mind that freezing is NOT considered humane anaesthesia for amphibians (or reptiles for that matter) - so rather use them as feeders in season and make another plan for "off season"
OR try to induce artificial breeding seasons by controlling light and water cycles etc. We don't breed most of our frogs so can't help you too much there (it usually involves cooling them which would mean we need to take them off display) but you will find plenty of info online...
... see literature below re freezing of amphibians and reptiles, there was a much better and comprehensive article, but can't find it right now.
"Freezing is *NOT* a humane method of killing for any amphibian. Although the frogs becomes torpid, it remains conscious and dies in agony as ice crystals slowly rip it's muscles and organs apart. Likewise CO2 is not appropriate for amphibians, which can survive under severe oxygen debt."
"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"
"4. Unacceptable methods of euthanasia for amphibians
4.1 Freezing. Any use of freezing in euthanasia must be approved as a special circumstance by
the IACUC. Freezing is only acceptable if the amphibian is small (<40 grams), is already
anesthetized, and the freezing is immediate (such as immersion into liquid nitrogen).
However, refrigerator freezers are too slow and are considered unacceptable. Additionally
many artic, near artic, and montane species can tolerate freezing for over 48 hours, making
this especially ineffective for these species.
4.2 Trauma. Due to the ability of many amphibians and reptiles tolerating severe traumatic
injury, trauma is unacceptable as a method of euthanasia. Only special circumstances using
trauma will be allowed and only if approved by the IACUC prior to any activity. If approved,
the PI must demonstrate that the cranium and brain are destroyed in one blow.
4.3 Carbon dioxide. CO2 is an accepted method for humane euthanasia for birds and mammals.
However, as reptiles and amphibians can survive under severe oxygen debt it is not
acceptable for use in these animals.
5. Humane Methods of Euthanasia for AmphibiansDivision of Research Animal Care Facility Standard Operating Procedure
SOP 302.01 – Amphibian Euthanasia 2
At this time several methods of euthanasia are accepted by the National Research Council on Pain and
Distress in Laboratory Animals.
5.1 Tricaine methanesulfonate (MS‐222). Overdose at 200 mg/kg of body weight injected into
the body cavity.
5.2 Ethyl alcohol. By sedation in a bath of 5% ethyl alcohol (ethanol) followed by immersion into
a stronger bath after the amphibian has been anesthetized.
5.3 Pentobarbital. At 100 mg/kg injected into the body cavity.
5.4 Pithing. Anesthetized amphibians can be pithed.
6. Using Orajel
Benzocaine. Orajel® (and other painkillers containing benzocaine) appears to rapidly anesthetize and
euthanize amphibians. This method has not yet been accepted by the National Research Council on Pain
and Distress in Laboratory Animals, probably due to how recently the publications involving these
products have come out. Products containing either 7.5% or 20% benzocaine have been shown to be
effective in the euthanasia of amphibians. The original descriptions of this procedure had the gel
containing the benzocaine applied to the head of the amphibian, however it has been shown that it may
be more effective if applied to the ventral (belly) surface of the animal (this may actually be most
effective in anurans, which have pelvic patches, rather than caudates). A 5‐mm drop applied to the
ventral surface of a Eurycea quadridigitata resulted in relaxation and death in less than one minute
(Chen and Combs, 1999).
The topical application of Orajel for euthanasia is a simple procedure. The investigator squeezes a
"dollup" of cream from the tube onto a finger and applies the gel to the ventral surface of the
amphibian’s body. For amphibians, the gel should be applied on the pelvic patch, for salamanders and
caecilians; the ventral body surface can be covered with gel. Following application, the animals are
placed in plastic bags until they succumb to the effects of the benzocaine (active ingredient of Orajel)