Even with the best care, it can happen that a fish becomes terminally ill. If a fish is clearly in distress and there is no prospect of healing, the question arises as to how the fish can be put out of its suffering.
The methods presented here kill the fish quickly and safely without causing additional torment. Please do not understand any of the content as a request – leave all measures only in consultation and through your attending veterinarian.
Please note that this page treats all information without guarantee and has no guarantee of correctness. Furthermore, online information does not replace a visit to the veterinarian. If you have any questions about medication, diseases or applications, we strongly recommend that you consult a veterinarian. In addition, this text in no way constitutes a request to kill fish.
clove oil
The basic procedure.
At least four drops of clove oil from the pharmacy are dissolved per liter of water in a container with aquarium water. It makes sense to first dissolve the required amount of clove oil in a small amount of warm water. The water is vigorously shaken. The resulting mixture is then poured into a jar with the fish. Alternatively, the fish can be placed in the water only after the clove oil and all the water needed are well mixed.
If the clove oil is simply added to the water, oil droplets form on the surface and it mixes very poorly with the water. It will then take longer to stun the fish and a larger amount will be required. If a fish swallows unmixed oil, it may experience convulsions. There is no reliable information on this. In agony, fish often convulse before the anesthetic takes effect, despite the clove oil.
Syringe method.
The oil is distributed well when the required amount is drawn up into a syringe. A few milliliters of water and some air are added. The syringe is shaken vigorously until a milky white or cloudy emulsion of oil, water and air is formed. This emulsion is injected into the water from the tip at high pressure. The water is also stirred so that the oil is evenly distributed.
Method with liquicell bottle and haribodose.
A small, empty bottle of Liquizell from Hobby can be used instead of a syringe. Round 1 kilogram cans from Haribo are well suited as containers for sick fish up to the size of dwarf cichlids.
One liter of aquarium water is filled into a well-cleaned Haribo can and the sick animal is used.
The lid of the Liquizell bottle is unscrewed and the bottle filled with aquarium water. About 20 drops of clove oil are added. The lid is screwed on and closed with the cap. The bottle is then shaken vigorously for about 5 minutes until the emulsion is formed. The cap is pulled off and the emulsion is squirted into the container with the sick fish.
Dwarf cichlids measuring around 5 centimeters are dead after 1 to 2 minutes.
The mode of action.
The clove oil stuns the fish. At the recommended amount, the fish will be paralyzed from breathing, allowing it to suffocate during the stun without suffering.
The fish becomes calmer and the muscles relax. Finally, the fish lays on its side. He falls asleep and loses consciousness. Eventually he dies of respiratory failure.
This method is a safe and gentle approach that can be used by any aquarist.
The dosage.
There are different experiences with the dosage. Sometimes it is recommended to first stun the fish with 4 drops per liter and then to refill with 20 drops per liter. The variant of using 20 drops per liter directly should also kill the fish. According to other sources, 0.5 milliliters of clove oil should be used per liter of water, but no more. The reason is not known.
The vodka method
The following method is probably the best for killing aquarium fish:
- Pour the aquarium water into a measuring cup or another container depending on the size of the fish.
- Write down the amount of water in the measuring cup.
- Place the fish in the measuring cup.
- If the measuring cup is clear, wrap the measuring cup with a dark cloth to calm the fish.
- Fill a small, clean mug, glass, or small bottle with aquarium water, leaving some space at the top.
- Depending on the size of the fish, drop 1 to 4 drops of clove oil per liter of water in the measuring cup into the small cup.
- Shake the small cup vigorously until a milky-white emulsion forms.
- Pour about a quarter of the emulsion into the measuring cup.
- After about 10 minutes, the fish lies dead on the ground and is only breathing very easily. If this is not the case after 10 minutes, the small cup with the emulsion is shaken again and the same dose of emulsion is poured into the measuring cup.
- If the fish is sleeping on the bottom, pour 20 to 25% of the indicated amount of grain alcohol, such as vodka, into the measuring cup. For example, add 60 milliliters of vodka to 240 milliliters of water. Leave the fish in the mixture for at least 20 minutes.
- After about 20 minutes, check whether the gills are still moving. If the gills don’t move for 60 seconds, the fish has died.
It is wrong to use the vodka with the clove oil together. The vodka is only used in a second cut when the fish is already stunned by the clove oil. Vodka is too stressful for an unanesthetized fish.
Clove Oil and Labyrinth Fish
There are some concerns expressed about using clove oil on labyrinth fish. According to this, there is a fear that labyrinth fish will panic and suffocate if they try to gasp at the water surface due to the anesthetic and fail to do so. The analogous argument would then also have to apply to fish that only breathe through gills if no water flows past the gills due to their inability to move. Most labyrinth fish also breathe through gills and only in special cases breathe through the labyrinth organ. It can be assumed that all fish species are completely stunned before agonizing death by asphyxiation threatens.
To be on the safe side, labyrinth fish can be placed in water that is 3 to 4 centimeters high. This will allow them to comfortably surface until the anesthetic kicks in.
Another concern is that clove oil could deposit on the labyrinth organ and cause painful suffocation of labyrinth fish. Why clove oil should cause suffocation of mazes but not suffocate fish that only have gills is unclear. A different effect on gills and labyrinth organs is not known for either dissolved oil or undissolved oil.
Apparently there are no confirmations from practice for problems with the correct use of clove oil, especially with labyrinthists. There is experience with the use of clove oil in labyrinth fish.
Problems with the use of labyrinth fish and other fish are probably caused by insufficient mixing of clove oil and water, which does not form an emulsion.
Heart stab/gill cut
Use a sharp knife, knitting needle or sewing needle to poke from below between the pectoral fins towards the head. Death is immediate.
Using a scalpel or sharp knife, cut into the gills towards the caudal fins. The fish will suffocate within a few seconds.
The advantage of both methods is that the fish is slaughtered and killed immediately.
These methods can be learned in any fishing course and, when done correctly, are the fastest and most humane methods.
The methods are difficult to apply to small fish. If used improperly, there is a risk that the fish will not be killed immediately and will experience additional torment.
neck cut
With a sharp knife or sharp scissors, the neck of the fish is severed with a quick, forceful cut. The cut should be just behind the gill covers. In the case of small fish, the head can be cut off completely.
When used correctly, this method is safe, quick and painless. However, without practice it is not easy to hold the fish and cut quickly and vigorously in the right place. With larger fish, there is then a risk that a cut will not kill the fish immediately and the fish will suffer additional distress. In addition, fish can show apparent signs of life even after the spinal cord has been severed, such as wriggling.
Photo: Class
Female dwarf gourami killed by cutting the neck with scissors with the right hand and immediately afterwards pouring boiling water over it with the left hand.
Powerful blow
The fish is wrapped in a cloth. The head of the fish is hit hard with a heavy hammer. Alternatively, the cloth is slapped vigorously against a solid surface. Because the brains of fish are relatively loosely attached to the skull, death is instantaneous.
This method sounds brutal, but when done correctly, it is safe and quick. Death comes so quickly that the fish feels no pain. If the hits are too weak or undirected, there is a risk of torturing the fish.
ice water
So much salt is dissolved in warm water until the water is saturated with salt, ie until no more salt dissolves. This water is placed in a freezer compartment or freezer for several hours. The salt makes the water ice cold without freezing. The temperature should drop below -16°. A smaller fish placed in this water will die instantly without feeling pain.
Smaller fish die almost instantly. In the case of larger fish, it is unclear how quickly they really die and whether they do not feel pain. Due to the cold shock, however, the sensation of the cold stimulus is suppressed in a flash. The circulatory system probably fails immediately as a result of the cold shock, the heart stops and all vital functions come to a standstill.
Instead of water, 50-70% alcohol can be used, eg isopropanol. No ice crystals form on the edge of the container either.
The temperature is best measured with a thermometer.