Dealing with the Inevitable: Most Humane Way to Put Down a Fish

It is inevitable that our finned friends need to leave us. If euthanasia is required,we ought to minimize the fish's suffering in a dignified and humane way. If you are not comfortable in resolving these issues, you should seek the advice and/or assistance of a professional.

These methods have been popularly used for preparing fish for human consumption.

• Bonking and pithing: percussion to the brain, followed by physical separation of the brain from the brain stem, via incision between the skull and first cervical vertebrae, and followed up with pithing[i]. See video.
• Ikejime/ikijime (活け締め/活き締め): locate the brain of the fish, then quickly and firmly insert the spiking tool into the brain, follow up by wiggling such tool to ensure complete destruction of the nervous tissues[ii]; this method is believed to preserve flesh quality the best. See video.
• Cave man: repeat percussions to the fish’s head, as close to the brain as possible, until the fish stops moving. 

Human consumption may not be advised for fish euthanized through chemical sedation.

• Benzocaine hydrochloride, sodium pentobarbital, and MS222[iii], or clove oil[iv] are commonly used to painlessly euthanize the fish but may adversely affect human health, e.g. clove oil may be a weak carcinogen[v].

The following are not considered humane methods of putting down a fish[vi],[vii]:

• immersion in ice water bath 
• boiling the fish alive 
• asphyxiation by removal from water 
• bleeding out without stunning 
• immersion in water with extra carbon dioxide added 
• immersion in salt or ammonia baths 
• flushing down the toilet 

Sources:
[i] Royal Society for the Prevention of Cruelty to Animals Australia Incorporated, “What Is the Most Humane Way to Kill a Fish Intended for Eating?,” RSPCA Australia Knowledgebase, August 16, 2012, http://kb.rspca.org.au/print/451/.
[ii] DigsFish Services Pty Ltd, “Ikijime,” Ikijime, 2014, www.ikijime.com.
[iii] Neale Monks, “Aquarium Fish Euthanasia,” Fish Channel.com, accessed April 5, 2014, http://www.fishchannel.com/fish-health/euthanasia.aspx.
[iv] London Drugs, “Rougier Clove Oil - 8ml,” 2014, http://www.londondrugs.com/Rougier-Clove-Oil---8ml/L0040402,default,pd.html.
[v] Monks, “Aquarium Fish Euthanasia.”
[vi] Royal Society for the Prevention of Cruelty to Animals Australia Incorporated, “What Is the Most Humane Way to Kill a Fish Intended for Eating?”.
[vii] Monks, “Aquarium Fish Euthanasia.”