EUTHANIZING A FISH

Sometimes an illness may not be treatable,or, a fish has progressed too far into the illness to make attempting treatment worth it. In some cases choosing to euthanize a fish is more humane than trying to treat it. This section will cover all the methods step by step of humanely putting down a fish. All of these methods start by painlessly putting the fish into a deep sleep using an initial dosing of an anesthetic, although that anesthetic may also be the euthanasia agent.

When to euthanize a fish:

When the fish’s illness develops too much and treatment likely will not help
If the fish has a fatal illness such as TB or Dropsy that is almost never successfully treated, and attempted treatment takes no effect.
When the fish shows little to no response to treatment of all kinds that are available to the specific illness.

How NOT to euthanize a fish:

Freezing. This involved placing the fish in the freezer, however this is painful as the fish can feel ice crystals in its body forming.
Boiling. This is boiling the fish alive, which while it is quick, it certainly is not painless.
Pithing, Decapitation, stunning, or other physical methods. If hesitating, these methods will not be painless or quick. This will not be simple and is not for the faint of heart.

Euthanasia Methods (with steps):

Clove Oil:

Clove oil can be used as a sedative for aquarium fish, but can also be used as a euthanasia agent. It is extremely effective and nearly equal to MS-222 in effectiveness. Clove oil is also known to have pain killer effects on people, which means it likely has the same effect on fish. However, it should not be used as a painkiller, as misuse will kill a fish.

Prepare a solution in a separate tank about ½ the size of the main tank or smaller (i.e. a small fish in a 55 gallon should be put in a 1-5 gallon tank for this, or a large fish in a 250 gallon could go in whatever small tank would accommodate it).
Approximately 400 mg (0.4 grams) of clove oil per litre (.27 gallons about) of aquarium water is enough to kill a fish with hypoxia after putting it into a state of unconsciousness. Include an air stone to ensure maximum circulation.
Add the fish for the solution and leave it for about 10 minutes. Check for gill movement. If there is any movement from the fish showing it may still be unconscious, add a few more drops of clove oil and check back in another 5-10 minutes. The fish cannot feel any pain when unconscious.

CO2 Overdose:

The CO2 overdose method will NOT work with labyrinth breathing fish like a betta as they will simply take a breath of air from the surface. However this method will render the fish unconscious before it dies of suffocation in it’s sleep.

Some people have mentioned the use of baking soda for this method of CO2 overdosing as well.

Using a pressurized CO2 tank, attach the CO2 tube to an airstone and place this in the tank. Turn the valve until there is a steady but good flow of bubbles from the airstone to increase circulation and also add the CO2 to the water.
With the CO2 displacing the Oxygen in the water, the fish will fall into a coma. Keep the C02 running for 10 minutes after the last noticeable gill movement to ensure the fish really has passed.

Anesthesia Overdose:

MS-222 (Tricaine methanesulfonate) and Benzocaine hydrochloride are commonly used anesthetics in the veterinary community. They are not available to the general public, but in some cases they can be legally obtained. This method involves dosing slightly more anesthetic than needed to put the fish into a sleep, so instead the fish will fall asleep and pass on. Water hardness/temperature, animal type/size, anticipated duration of procedure can all affect the needed dosages.

You will need: Sodium bicarbonate (prevent pH spikes), MS-222 or Benzocaine hydrochloride (anesthesias).

Don’t feed the fish for 24-48 hours prior to the procedure. MS-222 and Benzocaine hydrochloride are known to induce a stress period initially before the fish calms down. Not feeding the fish will reduce the risk of regurgitation.
Transfer the fish to a smaller tank, at least ½ the size of the current tank, so the dosing is more effective and more easily circulated. Be sure to add an air stone to properly circulate the anesthesia around the tank.
For MS-222, the general dosage calculation is as so: dosage (mg/liter) x volume (liters)/1,000= amount MS-222 (grams). The sodium bicarbonate general dosage calculation is as so: MS-222 x 2= amount sodium bicarbonate. It should be about a 1:2 ratio for anesthesia:sodium bicarbonate.

Chart from https://www.advancedaquarist.com/2010/11/fish #99 in REFERENCES:

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