Diseases in The Aquarium: Sedation ~ Anaesthesia ~ Euthanasia
Written by Tuesday, 08 January 2002 01:00
Sometimes we need to transport fish and we want to reduce their stress and metabolism, which will result in less oxygen consumption and less production of organic waste. In this case we must induce sedation. Whenever we want to perform a [ simple ] operation on fish (e.g. remove a nodule from their body or a foreign particle from their mouth) we need to induce anaesthesia. In more severe cases, we may have to humanely destroy the fish since the disease has already progressed too much and there is no way of recovery. In this case we have to euthanize the fish.
The difference between the sedation, anaesthesia and euthanasia lays in the concentration of the chemical used. Hence extreme care is required when using these chemicals; overdosing means the fish may be severely harmed or even euthanized instead of being anaesthetised. In cases like this it is preferable, when possible, to seek advice and/or assistance from a vet or someone who has experience in performing such tasks.
The recommended concentrations of the chemicals that can be used are indicated below:
Benzocaine
1) Anaesthesia: Add 50-500 mg benzocaine / l.
This concentration will bring anesthesia within 60 seconds.
2) Euthanasia: over 500 mg benzocaine / l. When euthanizing a fish it is recommended leave the fish in the water for 10 minutes after all breathing stops before disposing the body.
Carbon dioxide
This is a last resort since the dose is difficult to control and it is easy to overdose and cause death by hypercardia.
1) Anaesthesia: Add 200 - 400mg/ l (by bubbling the gas through water) - Anaesthesia should occur within 5 minutes
2) Euthanasia: bubble CO2 through water till death occurs. When euthanizing a fish it is recommended to leave the fish in the water for 10 minutes after all breathing stops before disposing the body.
Quinaldine sulfate (Quinate)
1) Sedation : Add 1-50 mg of Quinaldine sulfate / l
2) Anaesthesia : Add 2.5 - 100 mg Quinaldine sulfate / l (anesthesia occurs within 60 seconds)
3) Euthanasia : Add the same quantity as for anaesthesia. When euthanizing a fish it is recommended to leave the fish in the water for 10 minutes after all breathing stops before disposing the body.
Sodium bicarbonate
This is a last resort since the dose is difficult to control and it is easy to overdose and cause death by hypercardia.
1) Anaesthesia : Add 1 tablet of Alka-Seltzer / 20 liters - or 200mg/liter.
2) Euthanasia : Add 30g of NaHCO3 and dissolve completely. When euthanizing a fish it is recommended to leave the fish in the water for 10 minutes after all breathing stops before disposing the body.
Tricaine (Finquel)
1) Sedation (for transporting fish): Add 10-40 mg Tricaine /l (you can raise it to 100 mg/l if fish are too many or too crowded)
2) Aanesthesia : Add 50-250 mg Tricain / l. The optimum concentration will bring anaesthesia within 60 seconds
3) Euthanasia: same dose as above (anaesthesia). When euthanizing a fish it is recommended to leave the fish in the water for 10 minutes after all breathing stops before disposing the body.
Fish can also be euthanized by:
Dropping the temperature (Gradual freezing): fish are placed in a fish transport bag with enough water (at least one liter for small fish, more than 3-4 liters for a big fish) to keep them from freezing instantly. The bag with the fish is then placed in the freezer and should be left there for at least 2 hours after all the water has turned to ice. Only then can the bag with the body be discarded.
Concussion / Decapitation: Decapitation is considered an acceptable way of euthanizing small fish, whose head can be removed quickly with a sharp knife. Following this some authors advise to concuss the fish. The reason is that "fish's brains are highly tolerant of HYPOXIA .. such that the animal may remain 'conscious' for some time after its head has been severed from the body" (A-Z of Tropical Fish Diseases and Health Problems, p. 266). Concussion, i.e. destroying the brains of the fish by hitting its head with a heavy object, is also currently considered to be amongst the humane methods of killing larger fish. To concuss bigger fish we need to wrap their body with a towel (so that we can grip it firmly to immobilize it) prior to hitting it on the head. This destruction of the brains of the fish leads to immediate death. This method may upset some individuals and may also lead to unnecessary suffering of the fish if not performed skilfully (i.e. by a trained person).
Euthanasia, also called humanitarian or mercy killing, is a sensitive topic amongst aquarists. The decision to euthanize a fish or not, as the case may be, is very much up to each aquarist and depends on their standpoint. The topic most certainly merits a thorough discussion, which, however, is beyond the scope of this presentation. Having said that, we would like to highlight some of the more pertinent issues around euthanasia.
Euthanasia is a "humane" way of disposing a sick or particularly elderly animals who are unwell due to their advanced age provided that:
- the animal will die in a short period of time anyway (i.e. there is no way it can recover),
- the animal will suffer - or will suffer considerably - if left to die of "natural" causes (disease, wounds, old age etc), in which case the aquarist's interference (euthanizing the fish) is sparing it the unnecessary pain, stress and suffering which it is about to go through and
- the ways employed to euthanize a fish will be totally painless or at least considerably less painful than what the fish is about to experience if it were not to be euthanized.
The above make clear certain assumptions underlying euthanasia. Namely:
- we are positive that the fish will die,
- We are positive that the fish will die in pain, will be unnecessarily stressed or suffering and there is no other way to prevent this (i.e. by isolation),
- we are positive that the method we are employing is "humane". Bear in mind that as our knowledge on fish health and biology expands, previously considered "humanitarian" methods of killing animals are subsequently seriously questioned and / or condemned (for example see the new evidence regarding the ability of crustaceans to feel pain in Practical Fishkeeping). Along the same lines, experts in the field occasionally disagree on the appropriateness of a particular way of euthanising fish. For instance, it has been argued that euthanizing fish "by slowly chilling them ...[though] still commonly advocated in the aquarium literature, ... is now considered to cause the fish unnecessary pain" (A-Z of Tropical Fish Diseases and Health Problems, p. 267). For the reasons indicated aquarists who would consider euthanasia, if required, for their fish, are strongly advised to seek the latest information available on the topic.
- We are realistic in the assessment of our abilities and we are positive that we can perform the actions required to euthanize a fish as these should be performed.
To avoid cruelty to fish if you are in doubt about any of the above or feel uncomfortable about performing the required actions it is highly recommended to consult an expert (e.g. vet).
Please remember to dispose of the dead fish hygienically. Incineration is currently considered the best way of doing so. Dead fish, particularly those who have been sick prior to being euthanized, should not be released in domestic waters or buried in places where they may be accessible to local wild life.
A final remark regarding euthanasia: how appropriate is it to apply "humanitarian" (i.e. pertaining to the human race) principles and human preferences on a different species? For the time being we will leave you with this as food for thought.
References
Chris Andrews, Adrian Exell and Neville Carrington, The Interpet Manual of Fish Diseases, Salamander Books Limited, UK, 1988.
Dick Mills, Tropical Aquarium Fishes, Tetra Press, Salamander Books Limited, UK, 1997.
Paul V. Loiselle, The Cichlid Aquarium, Tetra Press, 1994.
Edward J. Noga, Fish Disease, Diagnosis and Treatment, Mosby-Year Book, Inc, 1996.
Physician's Desk Reference (PDR) Medical Economics Company, Inc., 53rd Edition, 1999.
Gerald Basleer, The New Illustrated Guide to Fish Diseases, 1st Edition.
Burgess, Bailey and Exell, A-Z of Tropical Fish Diseases and Health Problems, Ringpress Books, 1998.
N.B. Please note that the tolerance of different species or even individual fish of the same species to chemicals varies. Similarly, the effectiveness of chemicals depends, in some cases, on the water parameters (kH, GH, temperature etc). If in doubt, it is recommended that you get advise from a specialist (e.g. vet). The authors cannot accept responsibility for any losses or damages related to applying chemicals or procedures presented in this article.
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