Ok, here it is, written by me a few years ago now (for English coursework of all things!):
As hobbyists, we sometimes have to make difficult decisions regarding the welfare of our fish. When a disease overwhelms the animal and we know that despite our best efforts it is not going to improve, we need to overcome our own selfish, squeamish feelings to do what is best. Recently, research has been carried out into fish sensory abilities, with the conclusion that fish can detect pain, contrary to initial beliefs, opening the door to a new wave of studies to discover the kindest way to let the creature pass away. Latest studies on this topic uncovered significant evidence in regards to certain methods of euthanasia, exposing some surprising results. Now, with the aid of the results of these experiments, the hobbyist can take a more educated and humane approach to putting down their pet.
All the specimines used in this experiment were required to be of identical size in order to accurately compare the results. The specific fish chosen in this test were 3″ common goldfish, all happy and healthy beforehand, to ensure the test remained fair. It had been decided that the best way to analyse the pain level of the animal was to assess the level of stress hormone secreted in their bodies. This, however, presented a problem. How does one intend to obtain stress readings prior to the experiment without the penetration of the needle causing trauma and therefore rendering the results unreliable? Anaesthesia was ruled out as it too would distort the results, so the only way possible was to test the water surrounding the fish for the hormoe being secreted in their urine.
The fish involved in these experiments were conditioned in individual 18″x12″x12″ containers with 70% water changed performed daily. The water was tested for the hormone by using a Gas Photo Spectrometer and a Radon Gas Ioniser. The results obtained by the equiptment were recorded in a table and then translated as a rating from 1 to 10 for accessibility to the reader, with 10 being the most humane. The methods tested were CO2, clove oil, MS-222 (tricaine methanesulfonate, a fish and amphibian anaesthetic), freezing, ethanol bath (98%), para formaldehyde (cranial injection and submersed in 30% solution), potassium permangenate (cranial injection), spinal cord severance, decapitation and a hard blow to the head. These are the results obtained, graded from 1 to 10:
Clove Oil 7
Para Formaldehyde Bath 6
Para Formaldehyde Cranial Injection 9
Potassium Cranial Injection 9.5
Severing of the Spinal Cord 3
Hard Blow to The Head Ranging from 1 – 8
Obviously some of the above methods are unavailable to the average hobbyist, so a compromise must be made to find the most ethical way to let the fish die with what we can obtain.
Left: Dropsy is often the result of internal bacteria. Unless caught in the very early stages, the disease is almost always fatal
The Hobbyist’s Options
Notes: Freezing was often thought of as a very humane way to put a fish to sleep. The animal’s motabolism would slow down, go into a state of hibernation, fall asleep and peacefully pass away. Judging by the results obtained from the above experiment, this is not so, actually being the most inhumane method tested. I have used this method in the past but never been completely comfortable with it. Despite the results of this test, if your fish is in obvious pain and is not going to improve, you may have to face the lesser of two evils. Unless the fish is in extreme distress, I would not recommend it.
Procedure: Place the fish in a container of its own tank water and put it in the freezer. Wait long enough for the water to completely solidify as goldfish can survive being partially frozen. Try not to disturb the fish in this time.
Notes: Clove oil is often used as an anaesthetic in fish surgery and would seem an obviuous method. However, promotion of the wrong method of use has cast a shadow over its effectiveness. Many websites suggest using vodka to emulsify the oil allowing the fish to absorb it easily, yet the alcohol causes great distress to the fish and then consiquently, to the owner. I have had many emails from disturbed owners telling me how their fish has appeared to be in great pain, leaping about in the water during this so called “humane” process of euthanasia. If used properly, it can be quite a gentle method to use, as revealed in the table. It is also easily obtained through health food shops and pharmacies.
Procedure: Place the fish in a container of around half a gallon of its own tank water. Take some more water from the tank into a jar or bottle. Add around 10 drops of clove oil and shake vigerously until the mixture has completely emulsified. Gradually add the mixture to the fish’s container. Leave it in the solution for 10 minutes. Some people choose to decapitate the fish afterwards to make completely sure the fish is deceased and not just heavily sedated.
Severing of the spinal cord
Notes: This method needs a strong stomach.
Procedure: You can do this either under water or not. Place a sharp knife behind the gill of the fish and quickly cut through the spinal cord, taking the head clean off.
Hard blow to the head
Notes: Again, not for the faint of heart.
Procedure: Place the fish in a bag without water. Take a relatively heavy object and strike as hard as possible over the head of the fish. If you are likely to hesitate, try another method.
In conclusion, I would recommend the clove oil method above all else that the average hobbyist has close at hand. If you follow the instructions listed above, it is infallible and can put your mind at rest that you let your pet go in the kindest way you could.