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Someone told me that one can kill a fish by putting it in iced water. He stated that it'll kill the animal extremely fast and without any pain.

I have my doubts... Can anyone explain why this should work? Or is it nonsense?

Toby Speight
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OddDeer
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  • related - it's not painless – Raystafarian Dec 02 '15 at 16:20
  • @Raystafarian your related answer just lightly touches on freezing in the comments. See related What happens when a gold fish pond freezes? – James Jenkins Dec 02 '15 at 19:27
  • @choz :D Captain America fish on duty! – OddDeer Dec 03 '15 at 07:14
  • @JamesJenkins Yeah, it's just in reference as to what is deemed "humane" for (pet) fish, obviously it has very little to do with killing fish for food. I've never fished for food. – Raystafarian Dec 03 '15 at 10:07
  • Reminded me of: http://skeptics.stackexchange.com/questions/1569/is-it-possible-to-die-instantly – Will Dec 03 '15 at 19:46
  • Might be a better fit for http://pets.stackexchange.com/, flag question and note that if you want to request migration. Here's a similar question there: What's the least painful way to euthanize a fish? – WBT Dec 03 '15 at 23:13
  • when fishing the only way I've ever seen anyone kill fish is with a cosh. A quick rap to the back of the head and it's lights out. You could also insert a knife behind the skull severing the spinal cord, though in my experience this is used rarely –  Dec 04 '15 at 08:38
  • @WBT I don't think that there is a scenario besides being in the wilderness (the great outdoors) where you have to think about killing a fish with most primitive methods to eat it (so, to survive). – OddDeer Dec 04 '15 at 12:04
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    @OddDeer Sorry, I wasn't paying close enough attention to attribution in the comment "it's just in reference as to what is deemed "humane" for (pet) fish" - you probably want to edit the question to reflect the focus on a wilderness scenario. I know I generally don't bring an icemaker to the back country, and I suspect fish I find in already-icy waters have adapted to handle that. Your explanatory comment here doesn't seem to match the question as written. – WBT Dec 04 '15 at 14:37
  • @WBT Hmm... I think that it is reflected due to the fact that it's posted on "The Great Outdoors". I don't think that one considers to kill a pet-fish through iced water. There are a lot of far better options "in the civilization" and therefore this question would be completely senseless in such a context. It's like "Should I shoot a cat in the head or in the heart?" and you say "Hmm.. you might post this to pets?!". The site implies which "cat" is meant (a bobcat for example but surely not a common house-pet-cat). – OddDeer Dec 04 '15 at 14:51
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    In what survival situation would you have (a) tropical fish, (b) ice, (c) no other source of food, and (d) no way to get back to a civilized settlement that might have other food before starving?
    Also, the fact that Pets already has multiple questions about humanely killing fish seems to justify pointing to at least one of them.     – WBT Dec 04 '15 at 15:17
  • @WBT Sorry, I really don't know what's the problem :D Can you please just leave my question here on this site? Please? I didn't say anything about a tropical fish and the other three points are complete nonsense tbh. I don't want to offend you or something and I'm happy about your input but I really believe that the site always adds initial context to every post (fully automatic). – OddDeer Dec 04 '15 at 15:23
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    I'm not a mod, but I don't think your question makes sense as you're trying to explain it. It needs editing. The question makes sense in the context of Pets (it's even been asked there) and it might be a reasonable guess that you didn't know Pets.SE existed, but I cannot imagine any wilderness survival situation where one would have both ice and fish that are not adapted to icy water, unless one is a very poor planner (carried ice but not food) and still close enough to where one got the ice that it hasn't melted. Can you imagine and describe such a situation? – WBT Dec 04 '15 at 15:42

3 Answers3

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You can kill tropical fish by freezing them, or even just letting them cool down. From the outdoors perspective, most game and edible fish are not tropical. There is a post on a sister site Fish “coming back to life” after being frozen and there are many Google finds about frozen fish coming back to life. From personal experience I recall my grandfather putting a fresh salmon in the freezer and when days later we put it in the sink to defrost, it started flopping around still alive.

In short, putting most fish in cold water or freezing them is not going to reliably kill them. Some die, some don't. Whether it is humane remains questionable: I'm not sure there is enough evidence to support a conclusion on the fish's experience of being frozen. Many game fish (and pond goldfish) are frozen during winter as part of the natural life cycle.

Toby Speight
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James Jenkins
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Ice water will not kill any fish quickly. Some fish even live in ice or icy water. A tropical fish may go into shock, but it won't die right for a long time. I think people may believe the fish is dead because the body has stiffened, but that's just a function of the cold and doesn't indicate a dead fish.

The fastest way to kill a fish would really be to behead it, but that assumes you are cleaning it immediately, and it can also make filleting a little more difficult. An alternative is to pour distilled grain alcohol over the fish's gills. That will also kill it quickly as well. The best way in my opinion is to cut the gills out at the bottom of the gill covers. This bleeds the fish out, helping it to die and also has the benefit of improving the fish for eating.

Because they are cold-blooded, fish will live a long time, even if they can't be resuscitated. So all you can do is the best you can. Place a folded wet towel over the fish's head so it's in the darkness and it will calm down significantly. Anecdotally, it may help the fish as much as it helps you.

Toby Speight
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Escoce
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  • While out fishing, when the fish is small enough I've always just broke its spine by hand. That seems quick, humane, and efficient to me. – Erik Dec 02 '15 at 21:20
  • Decapitation doesn't cause instantaneous death (in fish or in humans). The chef Dave Arnold looked into the subject and recommends a spike to the brain, following by bleeding out. If you're trying to improve the fish for eating, there's also benefit to following up with a wire down the spinal chord. – Peter Taylor Dec 02 '15 at 21:47
  • @PeterTaylor I didn't say instantaneous death anywhere in my answer. – Escoce Dec 02 '15 at 21:58
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It is absolutely not humane - in fact it is by FAR one of the most CRUEL methods to euthanize a fish. Regardless of them being tropical or not, before they are sufficiently cold enough to die, their blood crystallizes and they basically end up with ice shards shooting through them. Ouch. This is a very common question on aquarium forums and message boards though.

A better method to euthanize a pet fish is to overdose it with clove oil in a bowl of its tank water (clove oil is ordinarily an anesthetic is smaller quantities).

A better way to kill a fish you want to consume (or pet fish if you have the knife and fortitude to do it) is to simply chop its head off in one blow. Or to sever the spinal column (I think that would do it).

BunnyKnitter
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    I would be interested in a reference that supports, freezing is cruel, and that fish "blood crystallizes". Many fish have natural antifreeze in their blood http://www.sciencedaily.com/releases/2010/08/100825103832.htm – James Jenkins Dec 02 '15 at 19:06
  • What do you think causes the "ouch" in crystalizing blood? Personally, but I am a mammal, don't have feelings inside my veins. Do you mean the heart attack or other things that follow the crystalization? – phresnel Dec 03 '15 at 11:17
  • @phresnel Remember that every cell contains water. The ice is going to form near the sensory neurons as well, and ice formed in blood can activate the sensory neurons, so you can feel the ice forming as pain. The only question is: Is the fish put asleep from coldness before the pain starts? Maybe yes, maybe no. – yo' Dec 03 '15 at 13:46
  • For humans for instance, most people who freeze to death first can't fall asleep from cold, only to get into a koma from the coldness and never wake up. But for the fish that survives it, the waking up is very likely quite painful. (Anyway, I don't say anything for sure nor provide any evidence.) – yo' Dec 03 '15 at 13:46
  • Sounds like chopping the head off is most "humane", how you native English speakers call it :) – phresnel Dec 08 '15 at 10:23