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Why don’t fish freeze to death in icy water? (hokudai.ac.jp)
85 points by baalcat 240 days ago | hide | past | web | favorite | 32 comments

Well, that's a funny thing, _some do_, or at least to the point where it makes no odds. I was touring around Iceland (a country I can highly recommend visiting) and we were at Jokulsarlon [0] (where the icecap carves into the ocean) and there were lots of what looked like dead fish there. They basically swim in from the ocean, seemingly catch hypothermia, and are a feast for seals.

The local "fishermen" came along, with wellies on, waded into the water, literally kicked the fish out onto the shore. One of the fishermen was kind enough to give us one of their catch. It was tasty.

Go to Iceland, it's awesome.


Having been convinced by my classmates to jump in with them, I can confirm the Jökulsárlón lagoon is very cold!

Iceland will probably be my next international trip.

There might also be another explanation:


My dad says when he went ice-fishing with my grandfather they would put caught fish in a bag in the trunk. The fish would freeze on the drive back home but as they thawed back in their kitchen they would come back to life and start flopping around. Others have reported this, too (1). I can only guess their interiors were not frozen, and just in some sort of dormant state.

We have a small fishpond in our backyard just outside of Boston (kind of like this one, but a little deeper: https://www.pondmarket.com/epdm-pond-liner-rubber-liner-coat...). We have a few comets and shubunkin. Every winter the fish go dormant, usually around late October or early November, sinking to the bottom half-hidden by dead leaves. The top eventually ices over a few inches. We keep the small pump going and try to break the ice bubble if it freezes over, but otherwise the fish are not active for 4-5 months (with one exception, described below), until warmer weather comes in mid-April. It's an amazing thing to see them slowly reactivate and start to take food again.

One winter the pond iced over and they were still swimming around a little (2) which I can't explain. It's the only time we've seen this in the past 6 or 7 years.

1. https://biology.stackexchange.com/questions/1661/fish-coming...

2. https://www.instagram.com/p/BAR4PG8pJrn/?taken-by=ilamont

When they thawed in the kitchen, were they perchance on a metal surface, or salted? If so, what you're seeing isn't resurrectionist fish, rather electrolysis inducing a galvanic response in the deceased nervous system.

I think it was more like this: https://www.youtube.com/watch?v=zOJZaGUx9JM

Huh. That's a new one to me. This quora link sheds some light on what may have happened in both situations:


I've seen this myself. My step-father used to go ice fishing, and his catch would quickly freeze on the ice. He'd bring it home, fill the kitchen sink with water, and drop in the frozen fish. Some time later, there's be a fish swimming around in the sink.

Hmm, interesting. There was a pond in front of the office at Denver which was created when construction diverted some of the Platte river, and it had 3 or 4 fish 'stuck' in it. In the winter the water froze solid and I walked over and saw one of the fish sitting there frozen in the ice. I was tempted to try to chip it out but it was too deep and the ice too hard. About 3 weeks later the ice melted and the fish was swimming around again. It was pretty amazing to see.

Depending on the depth of the pond, it may have not frozen to the bottom - water has the highest density around 4°C (~39°F).

If the pond isn't very deep, and there's no streams or anything else coming into it that would oxygenate the water, usually the fish would die because of that. Happens all the time around here if water levels change drastically (say a beaver dam lets go), followed by a hard, cold winter with deep ice.

How do you know it was the same fish?

he could tell,they were connected.

Why would water (inside the fish) freeze in water (outside the fish)? I mean, the fish are swimming in the liquid form of water which apparently also doesn't freeze so why is it considered strange that they don't freeze? It would be strange if they didn't freeze while being in a block of ice, or if they would be dead blocks of fish-ice floating on liquid water. A non-frozen fish in liquid water is not strange, or am I missing something? The article doesn't really clarify it for me.

All bodies of water are not created equal.

The specific, and level of, solutes in the water determines the temperature at which it freezes. Fish are not perfectly permeable membranes, thus the internal freezing point of fish could be higher than the external freezing point of the water.

Fish are also cold-blooded and are at the mercy of their surroundings.

Or in other words you can freeze non-salt water in liquid salt-water; the salt lowers the temperature at which the mix freezes.

Human blood freezes at about -2degC. Brine can apparently go down to -20degC (source: Wikipedia).

> the salt lowers the temperature at which the mix freezes.

If you make ice cream the old fashioned way you throw in rock salt to lower the temperature below 0C.

You can also chill beer cans sitting in water very fast adding piles of salt to water.

You don't actually salt the ice cream. You put salt on ice surrounding the unfrozen cream. Salty ice cream (with the amount of salt necessary to freeze it) would be gross.

Available soluble salt ions lower the melting point of the water to the point where the water-ice would very much prefer to be salt-water at the same temperature. But a phase change requires energy, too. The energy required to melt the ice and dissolve the salt is taken first from cooling of the sugar-water in the cream, then from phase-changing it to solid crystals, then from cooling the solid-phase materials. If the setup has a paddle, that is mainly to transport heat from the center of the cream vessel to the conductive walls, and thereby regulate the size of the crystals.

Cooling beer cans in liquid water by adding salt does not rely on freezing point depression, but the heat of solution for NaCl in H2O, which also contributes slightly to the ice cream system above. You want cold beer fast? Use potassium nitrate (KNO3, saltpeter), as it has nine times the enthalpy of solution as NaCl.

I know since I've done it I've made ice cream that way, I guess I didn't explain it very well.

Some people have never made it that way, or any other way. Anyone who ever has made it that way would immediately understand.

What a hand-cranked ice-cream bucket might look like in ASCII diagram world:

   \\######|     |######//

The one I have has an electric more in place of the hand crank.

I also used to make it by putting the pot of cream mixture into a deep freeze still in the metal pot. Then get an electric hand mixer and mix it while it sat in the deep freezer. I'd do that over and over then for what seemed like 100 liters of milk and cream and hours of work I'd get 500ml of ice cream.

> adding piles of salt to water.

To ice water, not water.

I was thinking the same thing, but after re-reading it carefully, I think they simply mean "Why doesn't very cold water kill fish?"

I'm going to ask a staggeringly dumb question here:

Since none of the fish on Earth, which survive these conditions, live in zero-gravity, what is the reason for doing the experiment in zero-G? Given the immense cost of sending stuff to the ISS, there's clearly something about doing the work in zero-G that's either necessary, or highly advantageous.

Clearly the effect that keeps the fish alive works just fine under normal Earth gravity, or we wouldn't have an interesting question to answer.

I don't understand it either, but the article makes a stab at explaining why:

"Verifying the functions of these glycoproteins requires precise measurements of the normal growth rates of crystals over time. Yet this is difficult to do so on the Earth because of the natural convective flow around the growing crystal induced by gravity."

In the article they say that convective flow does not occur in micro-gravity which makes it possible to accurately measurement the ice crystals as they grow.

That makes sense, thank you. If you're already removing the flow that comes from the fish's own circulatory system, you may as well remove the remaining (comparatively small?) effects of the convective flow.

I don't know any of the details about why, but zero G is good for experiments on crystal formation.

Article says fish survive in sub zero environments such as below ice. But is the water below ice sub zero? I thougt it was at least zero as long as its liquid (at close to normal pressue). Is that the salt?

> Is that the salt?

Yes. Oceanic salt water freezes around -2C. (or possibly below as surface water freezes "pure", the salt content getting transferred to lower layers).

Some fish have antifreeze proteins:


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