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Managing Welfare During Euthanasia

Humane Aquatic Euthanasia

Euthanasia is an unpleasant but sometimes necessary aspect of animal healthcare, scientific research and aquaculture production. Aquatic animals in these systems may need to be killed for various reasons, i.e. at the end of an experiment, to sample blood and other tissues, when an animal or group of animals are no longer required or where the health or welfare of the animal is in question.

The welfare of these animals, even though death is the desired result, must be appropriately managed. The primary welfare criteria for animals being euthanised are that the method induces rapid unconsciousness and death, is painless and does not invoke a physiological stress response, requires minimum handling prior to or during the method, is appropriate for the age, species, and health of the animal, is reliable, reproducible, irreversible and is safe for the operator.

AQUI-S® is one such tool that will meet all animal ethics and welfare requirements. At high doses, AQUI-S® can be used to euthanise fish of any age or size and can be used on individuals or on groups. The following table provides an indication of the AQUI-S® dose required, depending on the species.


 Fin Fissh

100 mg/L - 40 min
175 mg/L - 20 min



250 mg/L – 2 hrs
500 mg/L - 40 min


200 mg/L 40 min
300 mg/L 20 min


When exposed to AQUI-S® at high concentrations, animals have been known to show an initial adverse reaction. If this reaction is deemed to be contradictory in terms of animal welfare, a lower dose of AQUI-S® can be used to sedate the animal prior to them being induced in the euthanasia dose. In general, animals will quickly lose equilibrium and reduce their opercular rate, before dying from medullary collapse.    

YES! Animal Welfare Can Be Managed During Euthanasia

Confirming Death

It is essential to ensure that the aquatic animal is dead before disposal. Confirmation of death in aquatic animals is, however, not a simple process. In general, a lack of opercular movement in fish or gill raking in crustaceans for at least 30 minutes is consistent with the death of that animal. Corneal reaction (tapping the surface of the eye) and pinching the tail fin will indicate deep anaesthesia but might not necessarily confirm death. The Iki Jime technique can also be used on deeply anaesthetised animals to ensure death. Read more on the Iki Jime technique HERE.


It is essential that all personnel carrying out euthanasia techniques are appropriately trained to recognise pain, fear, distress, insensibility and death for the specific species being euthanised.

Animal Disposal

Whilst humane euthanasia is the topic for this page, it is important to mention disposal of the carcass afterwards. Correct disposal is important to minimise any possible risk of disease spreading to fish populations in local rivers and streams. Operators must ensure that they comply with the applicable local legislation.

Inhumane Methods

There are many methods of fish euthanasia that are not considered to be humane and must not be used. These include hyperthermia, hypothermia, asphyxiation, carbon dioxide, carbon monoxide and decapitation.