Using clove oil to euthanise fish
DID YOU KNOW?
Clove oil is poorly soluble in water. One way to help it dissolve is to mix a measured amount of clove oil in a small amount of ethanol. An alternative method is to dissolve the clove oil in a small volume of hot water. Whichever method you use, you then further dilute the dissolved clove oil in some aquarium water until you reach the working strength. As a general guide, a dose of 10-15 drops of clove oil per litre of water is required to euthanise a sick fish. It’s best to use water from the fish’s home aquarium to dilute the clove oil as we don’t want to further stress the sick fish by exposing it to a sudden change in temperature, pH, chlorine, etc.
Make up the clove oil anaesthetic solution in a small clean vessel, such as a glass jar, and ensure it is mixed thoroughly. There should be plenty of depth to cover the fish. Before adding the fish, double check your maths to ensure you have not over- or under-dosed. You can then gently add the fish. Position it away from bright lights or other potential stressors.
Closely monitor the fish during anaesthesia. A hand lens or magnifying glass may help in the case of small fish such as guppies. You may see some erratic activity at first, but the fish should soon settle down and maybe roll onto its side as it falls into deeper states of anaesthesia. You should see the fish gradually lose body and fin movement and the gill beats will become shallow and maybe erratic. After a few minutes the fish should be completely motionless and not respond to being touched. Given the poor solubility of clove oil there is a real risk that the fish may still be alive, due to insufficient dosage. If you still observe any signs of life after say 10 minutes of immersion, add another dose (at 10-15 drops/litre) of clove oil. You may even need to repeat again, with a third dose, if necessary.
It might seem tempting to add a massive dose of clove oil at the very start, to ensure you have enough dissolved, but sudden exposure of a conscious fish to a very high dose of anaesthetic can be very stressful.