Euthanasia of koi carp

[Duncan]

Euthanasia of koi carp

Euthanasia (from the Greek: εὐθανασία meaning "good death": εὖ, eu (well or good) + θάνατος, thanatos (death)) refers to the practice of intentionally ending a life in order to relieve pain and suffering.

As koi carp hobbyists you can be sure at some point a situation will present itself where you will be faced with the situation whereby you need to end the life of a fish to prevent further pain and suffering. Just because it’s a fish does not mean it should not be approach with any less understanding and sensitivity than you would for a pet dog or cat or any other pet, although I would proffer that a dog or cat will pull at the heart strings a little more. Neither the less we will at some point be expected to do the right thing by our aquatic pets. While we can’t begin to understand the levels of pain a fish can experience or tolerate, we must however conduct this procedure in a humane manner.

Physiology

Carp have a slightly unusual physiology when compared to animals. The carp’s heart in the absence of oxygen will continue to beat for several hours being deprived of oxygen. Also in an animal once the brain is also deprived of oxygen the brain in a matter of minutes very quickly dies, whereas not so with carp. A carp’s brain when deprived of oxygen starts to produce ethanol which protects it during O2 deprivation and will protect it for several hours, both of which reasons are the reasons carp can be left out of water for several hours yet survive. In fact the crucian carp can last as long as 24 hours without oxygen rich water. All of Which is great when you have a fish that jumped out during the night, yet fully recovers when discovered the next morning when reintroduced to the pond water but not so good for obvious reasons when euthanasia is to be deployed.
Mechanical or chemical
All of the above presents us with several dilemma’s in so much as, a time and point of death is hard to determine, we do not understand the carps stress and pain levels, and we know from the outset because of these factors euthanasia is going to be a long and protracted affair. Precisely because of the aforementioned arguments will rage between mechanical and chemical methods of despatch with fishermen/angler preferring and opting for the mechanical method.

Mechanical method

The mechanical is as crude yet as fast as a single blow by a metal bar or weight across the head rendering the subject sense less and to all intent and purpose dead by cranial compression/concussion. fishermen particularly trout anglers have long since favoured this method with an object called a priest which is an end weighted metal bar swung on a leather thong across the head, there are arguments for and against this method however it does seem fast given that all other alternate methods seem long and drawn out.
Another mechanical method is freezing , although still relatively quick this does seem a step to far for most

Chemical method
The chemical method makes reference to the use of a chemotherapeutical in an administration drug overdose. This would include all anaesthetics traditionally used for the anaesthesia of a carp where the carp is left for a prolonged period of time rather than being maintained in a light to medium sedation. The list is fairly definitive and includes:
MS222
Benzocaine
2-phenoxyethanol
Oil of cloves (not recommended for euthanasia)

In all cases of overdosed sedation methods there is no real need to increase the dose rate of the medication, the act of increasing the dose alone will not speed up the time of death. To achieve a point of death you will merely need to leave the subject in a standard dosed solution for a prolonged period of time.

Once a carp is introduced to anaesthetic no matter how much anaesthetic is used the time line is as follows: light sedation-light narcosis-deep narcosis- light anaesthesia- deep anaesthesia followed by cardiac arrest. The time between light sedation and cardiac arrest in carp can be as long a few hours, so its recommended that once you see no gill movement the anaesthesia bowl should be covered and the subject left for a minimum of 6-8 hours.

The final dilemma, don’t dismiss the mechanical method out of hand, it’s a time honoured tradition for dispatching a fish and does have its merits, being speedy and over in an instance for both the fish and the owner. Whereas the chemo approach also has its advantages in that the fish simply goes to sleep (or so we think) and eventually although long and drawn out finally expires. None of us know how the actual event plays out from a carp’s perspective, so I will leave you the reader to decide as to which method you employ.

[Graham.]

Thanks Dunc, a great read.

It's never a nice thing to do but sometimes the old saying "cruel to be kind" seems the only way.

Having a nasty bacterial outbreak last year and seeing the Koi in such bad way I had to carry this procedure out on a few, knowing these Koi can be stuborn and hardly little sods when they want to be, I also take the route on once the medication is within the bowl and the Koi is lifeless then they are covered and left overnight.

Once again a great read.

Regards