We learn the habits and personalities of our pets and develop a kind of rapport with our aquatic friends.  This makes it ever so difficult when we see them struggling to survive and not the playful fish we once spent hours watching.  So, as it is with all living creatures, there comes a time when it is better to let them go in a decisive action, than to sit by and watch them suffer to the last struggling breath.

A respectful method by which to let them go is euthanasia.

There are many ways in which a fish can be euthanized.  They vary according to the adaptation of the fish to certain environments.  This topic is not well studied and consequently is limited in providing guidance as to the best method of killing a fish.

So, in view of the limited information available, it is appropriate to draw on correlative methods with other biological life.  Methods that seem not to cause pain or additional discomfort and result in the cessation of life in the creature at hand.

Chemical euthanasia is a tried and proven method.  The chemicals used induce a slow but steady loss of consciousness and eventual death.

The process involves administering an anaesthetic to the water in which the fish is residing.  As the fish breathes the water the anaesthetic is absorbed through the gills and into the tissue of the fish.  The anaesthetics often used by veterinarians are MS-222 tricaine methanesulfonate and benzocaine hydrochloride.

Since the dosage varies according to the size and fish species, it is best that a veterinarian be involved in euthanizing larger fish.  The dosage and rate of exposure can sometimes be difficult to administer.

Clove oil is another product that can be used to euthanize fish.  Clove oil is easily obtained and the results are almost identical to using veterinarian grade pharmaceuticals.

Clove oil acts as a sedative and is appropriate for use with fish in home aquariums.  The recommended dosage is 1.5 ml per U.S. Gallon or 1.8 ml per imperial gallon or 0.4 ml per litre.  It is suggested to mix the clove oil with warm water before administration to the fish water.

When administering the clove oil, take 5 minutes or so to slowly add the clove oil to the aquarium water.  A slow administration of clove oil is less likely to induce excitability in the fish.  Fish death will occur shortly after the fish loses consciousness.  The external sign of death will be the cessation of gill movement indicating breathing has stopped.  Keep the fish in the aquarium solution for at least 10 minutes following the cessation of gill movement.

Once the time period has elapsed remove the fish to a freezer to ensure death.  The fish should then be disposed of.

Other methods are available, but not always palatable for aquarists to implement.  They are:

1. Blunt Force Trauma: This method involves a quick and decisive blow to the fish’s head to cause instant death. This should only be performed by someone with experience to ensure a swift and painless death.
2. Carbon Dioxide (CO2) Sedation: This method involves using carbon dioxide gas to sedate the fish, leading to unconsciousness and eventual death. It’s considered humane if administered properly. Specialized equipment is often used for this method.
3. Decapitation: This method involves quickly and accurately cutting off the fish’s head. It requires skill and precision to ensure the fish doesn’t experience pain. It’s typically not recommended for people without experience.

Using the chemical process for euthanasia is often chosen in lieu of these other methods.

Regardless of the method chosen, it’s essential to ensure that the process is done as quickly and painlessly as possible. Additionally, it’s important to handle the fish with care and minimize any stress or suffering.

The procedure can be done in any container able to hold enough water along with the fish.  Aquarists might consider picking up a 5-10 gallon tank that can be used for this purpose.  Clear walls give a better view of gill movement, and that’s an important part of this process.

If you’re unsure about the proper method or if you’re uncomfortable performing euthanasia yourself, you should consider seeking the assistance of a veterinarian or a professional experienced in aquatic animal care. They can guide you through the process and ensure that it’s done humanely.