This is something I wrote up a couple months ago for my website, so I thought I would post it here too!
A question that I get asked a lot is “When do I know that it’s time to euthanize my fish? And how do I go about doing it?” Euthanasia is an unpleasant topic but unfortunately it is a necessary one to talk about. There are two main purposes for euthanasia in fish – to relieve the pain and suffering of a severely ill or injured fish, or to humanely destory fish with severe deformities (particularly fry).
When to Euthanize a fish
There are several diseases that effect are beloved bettas, that are consistently fatal, and euthanasia is sometimes the kindest thing we can do for our sick fish. The main fatal diseases in bettas are: Dropsy, Columnaris, and Fish Tuberculosis.
Dropsy isn’t a disease, but rather a symptom of other underlying problems, and there is no single underlying problem for every case. A fish with dropsy will be obviously round and swollen, particularly around the abdomen, the swelling causes the scales to stick out, and when viewed from the top the fish will resemble a pine cone. Fish suffering from dropsy are often lethargic, poorly colored, and uninterested in food.
The symptom that we call dropsy is essentially an accumulation of fluids within the body. As the body swells the scales are forced out, causing the pine cone appearance. The most common causes of dropsy are bacterial infections caused by poor water quality and maintenance, certain viral and protozoan infections, and organ failure.
Dropsy is extremely difficult to treat, by the time the fluid in the body has built up enough to cause the scales to pine cone, Severe internal damage has already occurred. By the time it gets to this point it’s usually best to euthanize the fish. You can try treating with Anti-biotics, epsom salt and increased water temperatures, but most of the time these treatments do not work, and you are just prolonging the suffering of the fish!
Columnaris is a bacterial infection caused by something known as flexibacter bacteria. The bacteria are most likely to infect fish that have been stressed by conditions such as poor water quality, inadequate diet, or stress from handling and shipping. Columnaris can enter the fish through the gills, mouth, or via small wounds on the skin. The disease is highly contagious and may be spread through contaminated nets, specimen containers, and even food.
Columnaris can be external or internal, though most cases tend to be external, it can also follow or chronic or acute course. The chronic cases progress slowly, and offer more opportunity for treatment. Acute cases spread quickly and can kill within hours. High water temperature speed up the course of the disease, however lowering the temperature will not effect or slow down the progression of the disease.
White spots on mouth, edges of scales, and fins
Cottony growth that eats away at the mouth
Fins disintegrate beginning at the edges
‘Saddleback’ lesion near the dorsal fin
Fungus often invades the affected skin
Rapid gilling in cases where gills are infected
Fortunately Fish Tb isn’t as widely spread as it used to be, with fewer and fewer cases being reported, but it is still out there, and fish keepers should know what to look for! Symptoms of Tb include loss of scales, loss of color, lesions on the body, wasting, and skeletal deformities such as curved spines. Tb is not treatable, and can be spread to humans through open wounds. If a betta is showing symtoms of Tb the best thing to do is euthanize the fish.
Severe injuries to the betta, such as large open wounds where bone is showing, are also times when euthanasia might be the best option. Fish with poorly developed swim bladders (“belly sliders”) and deformed spines are particularly common among inbred fish, such as some fancy livebearers. In this case, euthanasia removes bad genes from a particular batch of fish, ensuring each new generation is healthy and conforms to the standards of the type.
How Not to Euthanize
Submersion of the fish in ice water or boiling water are not humane, though ice water can be used in some situations while I will discuss later on. Suffocating the fish by leaving it out of water is also inhumane, as fish will remain unconscious out of water for long periods, in some cases several hours.
Acceptable Methods of Euthanasia
Clove oil is a sedative at low doses, but at higher doses it has been recommended by some researchers as an inexpensive way to euthanize fish, particularly small fish. In a container, mix aquarium water with clove oil and mix. When exposed to high concentrations of clove oil, fish quickly lose consciousness and stop breathing, both of which reduce pain. Hypoxia eventually causes death, and once verified, the fish can be removed from the water and clove oil mixture, some people choose to add alcohol to the clove oil and water which will cause the fish to pass on more quickly then the clove oil would alone.
Ice Bath Method
Tropical Fish less than 2 inches in length can be euthanized by exposing them to freezing cold water. The fish is put into a small container along with some aquarium water at the normal temperature. This container is then placed into a much larger container filled with crushed ice. This will rapidly chill the water in the smaller container, eventually rendering the fish unconscious. When death is verified, the fish can be removed.
While too difficult for most aquarists, stunning a fish, decapitating it and then pithing it (physically destroying the brain with a metal rod) is a humane way to euthanize a fish. Because fish can remain conscious for some time after decapitation, the pithing step is essential. If you don’t know how to pith a fish, then don’t use this method.
Disposing of Dead Fish
Dead fish should not be flushed, flushing can contaminate native fish populations. Dead fish should be burned, thrown in the trash (tightly wrapped in a paper towel), or buried in the yard (deep enough that scavengers will not dig it up)