Aquarium keepers will sooner or later be confronted with sick fish. Often a fish is sick if it does not behave ‘normally’ and the aquarist must try to make a diagnosis to cure the fish. In some cases, the treatment does not work or the fish is terminally ill. As frustrating as it may be, in this case, it is better to put the fish out of its misery and preferably as painless as possible for the fish.
Unfortunately, there is a lot of misunderstanding about the killing or euthanasia of fish. Many methods of killing are carried out without expert knowledge even though they are well-intentioned. But what about the suffering of the fish and what are the best methods of killing?
Why kill the fish?
The only good reason to kill a fish is when the fish is seriously suffering and can no longer be saved by medication and/or proper care. Incurably sick, malformed, and/or weakened fish can be put out of their misery as quickly and painlessly as possible. It is the aquarist’s responsibility to determine the time when it is better to perform euthanasia. Allowing the fish to suffer until it dies is not animal-friendly.
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If you really don’t mind killing the fish, you can always have someone else assist you or have it done by another person. In addition, you may have to sacrifice one or more fish to the vet to find out the cause of a disease, infection, or fish death in your aquarium. Other reasons such as overpopulation, no good looks, or superfluous fish are not animal-friendly reasons to kill fish. Always try to look for solutions if you want to get rid of your fish. You can also offer them for free in shops and/or to other aquarists.
Do fish feel pain?
This issue leads to contradictory answers within science. Some scientists believe that fish feel little or no pain because the fish responds to pain through a reflex mechanism and that the fish’s cerebral cortex is poorly developed. Other scientists, on the other hand, believe that fish do feel pain because they have a thalamus that transmits the pain sensations.
The most obvious conclusion is that the fish does experience pain because it has a cerebral cortex and thalamus, necessary for the sensation of pain. In addition, several studies show that there are anatomical and psychological similarities with humans. Unpleasant stimuli are also avoided by fish. A German study has also shown the effect of painkillers on fish.
Animal-friendly killing methods
These methods apply to cold water and warm water fish as well as fresh water and seawater fish.
Using anesthetics is a painless and convenient method of euthanizing fish. With an overdose of an anesthetic, the fish will fall asleep peacefully, not recover and die. The anesthetic is always administered through the water so that it is absorbed through the gills of the fish. At first, the fish will usually calm down, after which it will fall asleep and die. This method is animal-friendly and humane euthanasia that allows the animal to pass without suffering. Various anesthetics can be used, namely:
- TMS (tricaine methanesulfonate)
- Methomidate HCL (etomidate hydrochloride)
- MS 222 (methanesulfonate 222)
- Eugenol (clove oil) (0.5 ml to use 1 liter)
- Benzocaine (mix 5 grams with 25 ml acetone and then use 2 ml on 1 liter)
- 2-phenoxyl-ethanol (5 ml to be used on 1 liter)
The first three products are only available to veterinarians. You can obtain the last three from the pharmacist.
Before you put the fish in the water, it is important to stir the mixture well so that the liquids are well mixed. It only takes a few minutes for the fish to die, but it is still important to leave the fish in the anesthetic long enough to make sure it does not recover and is definitely dead.
A hard blow to the head
This is a fast and effective method of killing that must be done with accuracy and right the first time. If this is not the case, the suffering of the fish can be very severe. By a correct hard blow to the head, the brain is destroyed and the nerve impulses can therefore no longer develop. The fish dies immediately.
Decapitation with anesthetic
Decapitation and decerebration is a quick and painless method of killing, provided it is done with the appropriate tools in the right place and with a steady hand. Unfortunately, this is very difficult and you can decapitate incorrectly. You have to cut the brain to destroy it beyond repair. A decapitation should always be preceded by an anesthetic.
Decapitation alone allows the neurons in the brain of the fish to remain active for a while after decapitation, causing pain signals to be produced. After a while, these cells will also die due to the absence of oxygen and blood supply, but we cannot speak of a painless death. If you want to decapitate a fish, it is recommended to stun it first.
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Other methods of killing
Many other killing methods used to cause the death of the fish, but are not animal-friendly and certainly not painless for the fish. Methods such as boiling water, ice-cold water, asphyxiation, poisoning, throwing in the toilet, etc. are therefore unacceptable.
Freezing in the freezer is also not acceptable. Due to the gradual cooling, the metabolism of the fish slows down and it goes into shock, but the neural pathways remain intact. The fish eventually dies little by little from organ failure.
So be human and opt for an animal-friendly euthanasia method if you ever face the difficult task of killing a fish.