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That fish looks alive until you know it isn’t. That’s incredible. I’ve wondered many times how it’s possible that fish in deep frozen winter rivers can survive

That fish looks alive until you know it isn’t. That’s incredible. I’ve wondered many times how it’s possible that fish in deep frozen winter rivers can survive given that they have such limited food and need to expend energy to stay in one spot… But I suppose this simplifies the equation. They can rest where the current allows for this phenomenon.

franciscop 5y ago
Alternatively, I learned in fluid dynamics that there's a gradient of velocity of the water circulating through any pipe; closer to the walls/floor it's speed is effectively 0, closer to the center it's at the maximum speed (in an ideal pipe/laminar fluid, that is barring turbulences/rocks/etc). In the real world there's definitely pockets of water within the river were the water speed is insignificant/still. https://accendoreliability.com/fluid-flows-pipes/ https://accendoreliability.com/fluid-flows-pipes/ https://en.wikipedia.org/wiki/Laminar_flow https://en.wikipedia.org/wiki/Laminar_flow
- steve_adams_86 5y ago
  That’s a great observation too. I wonder if areas like these would cause fish to congregate, which might explain why animals like minks can readily find fish under the ice. There’s so much I don’t know, haha.
  - munificent 5y ago
    > I wonder if areas like these would cause fish to congregate Any fisherman, especially one who fishes rivers, has a wealth of intuitive understanding of what kinds of water features lead to greater concentrations of fish and indeed a lot of it has to do with depth and turbulence. You'll often hear them talking about whether a patch of water looks "fishy" or not, and that often has to do with how still or turbulent the surface is (along with many other factors).
    - steve_adams_86 5y ago
      Incidentally I grew up fly fishing and that’s something I (hopefully) know a bit about! I’m just not sure about winter, under the ice. I’ve never fished an icy river (or an icy anything, come to think of it).
locallost 5y ago
Fish can stay in one spot with little effort also because they have a special organ called the swim bladder. They can fill it up with gas and this allows them to maintain their position without actually swimming.
- bombcar 5y ago
  Doesn't the swim bladder just help them calibrate depth in the water?
  - the_af 5y ago
    I don't think the parent commenter is saying the swim bladder is all that matters. There is an "also" hidden in their sentence :)
  - locallost 5y ago
    I'm not an expert, I just had to learn the basics recently to get my fishing permit. But the explanation given was that its function is allowing the fish to float / hold their position and save energy. Carps even have two chambers since they are bottom feeders and they can tilt their bodies mouth down more easily this way.
    - krisoft 5y ago
      Yes. What you are talking about is a fish keeping a fixed depth. Having a swim bladder enables the fish to attain neutral buoyancy. That way the fish doesn't need to expand energy to keep itself from sinking or floating up. What the article is talking about is position keeping against the current in flowing water. Swim bladder is good for up-down position keeping, the article's phenomenon is good for forward-backward position keeping. Interestingly there is a way to use a swim bladder like construct to propel one forward. Underwater gliders do this, and the process is very energy efficient. The way it works is that the glider uses its variable buoyancy device (an artificial swim bladder) to set a negative buoyancy and starts sinking. The wings of the glider turn this downward motion into forward speed. At the target depth the glider expands some energy from its batteries to set a positive buoyancy and keeps the forward momentum as it is ascending. Because of this they only need to use energy at two points (at the top and the bottom) in their saw-tooth like swim profile, and they can travel thousands of kilometers on a single charge. https://en.wikipedia.org/wiki/Underwater_glider https://en.wikipedia.org/wiki/Underwater_glider
NAR8789 5y ago
The fish is not merely holding position--it's actually accelerating upstream! Reminds me of this Tadashi video: [How do fish swim so quickly?] https://www.youtube.com/watch?v=wYDh5d9pfu8 https://www.youtube.com/watch?v=wYDh5d9pfu8 Tadashi shows that fish turn drag into thrust by swapping the positions of the vortices they shed. Low effort, high output. TFA takes this one step further--fish bodies are shaped to effortlessly harvest thrust from drag. No effort, free energy!
- a3w 5y ago
  TIL: The first law of thermodynamics has an exception for dead fish. (JK, don't cite me in physics class!)
  - munificent 5y ago
    Well, actually... In this case, the fish isn't a closed system. It's harvesting energy from the moving water, which requires external energy from the sun to keep the water cycle going.
  - bocytron 5y ago
    Reminds me of Derek's video about a vehicle which is powered against wind: https://youtube.com/watch?v=jyQwgBAaBag https://youtube.com/watch?v=jyQwgBAaBag
    - Maursault 5y ago
      His claim about a sailboat not being able to exceed windspeed sailing directly downwind is deceiving because it is definitely not the fastest point of sail. I believe this is done for dramatic effect to make Blackbird's feat sound more incredible. Sailing close hauled, almost directly into the wind, can achieve double wind speeds near effortlessly on low draft racing multihulls, and possibly on land with whatever those sailing carts are called. Of course, directly downwind is the only course for this experimental propellor craft, thus the only criteria.
      - 5y ago
kuhewa 5y ago
Besides energy saving behaviour, the metabolic rate has been depressed due to the physicochemical effects of cold, typically a reduction of 2-3x per 10 degrees. In terms of having enough energy, energy stores accrued during summer and autumn go a long way, but many fish are indeed a negative energy flux state over winter. In fact, over-winter starvation in the first year or three is a common ecological bottleneck, where even if fish are capable of reproducing and adults are fine and can survive the first year, the 0+ age class may not have had sufficient time to store enough energy before winter to survive until spring.
scoot 5y ago
> That fish looks alive until you know it isn’t. Schrodinger's fish.

franciscop 5y ago

Alternatively, I learned in fluid dynamics that there's a gradient of velocity of the water circulating through any pipe; closer to the walls/floor it's speed is effectively 0, closer to the center it's at the maximum speed (in an ideal pipe/laminar fluid, that is barring turbulences/rocks/etc). In the real world there's definitely pockets of water within the river were the water speed is insignificant/still. https://accendoreliability.com/fluid-flows-pipes/ https://accendoreliability.com/fluid-flows-pipes/ https://en.wikipedia.org/wiki/Laminar_flow https://en.wikipedia.org/wiki/Laminar_flow

steve_adams_86 5y ago
That’s a great observation too. I wonder if areas like these would cause fish to congregate, which might explain why animals like minks can readily find fish under the ice. There’s so much I don’t know, haha.
- munificent 5y ago
  > I wonder if areas like these would cause fish to congregate Any fisherman, especially one who fishes rivers, has a wealth of intuitive understanding of what kinds of water features lead to greater concentrations of fish and indeed a lot of it has to do with depth and turbulence. You'll often hear them talking about whether a patch of water looks "fishy" or not, and that often has to do with how still or turbulent the surface is (along with many other factors).
  - steve_adams_86 5y ago
    Incidentally I grew up fly fishing and that’s something I (hopefully) know a bit about! I’m just not sure about winter, under the ice. I’ve never fished an icy river (or an icy anything, come to think of it).

locallost 5y ago

Fish can stay in one spot with little effort also because they have a special organ called the swim bladder. They can fill it up with gas and this allows them to maintain their position without actually swimming.

bombcar 5y ago
Doesn't the swim bladder just help them calibrate depth in the water?
- the_af 5y ago
  I don't think the parent commenter is saying the swim bladder is all that matters. There is an "also" hidden in their sentence :)
- locallost 5y ago
  I'm not an expert, I just had to learn the basics recently to get my fishing permit. But the explanation given was that its function is allowing the fish to float / hold their position and save energy. Carps even have two chambers since they are bottom feeders and they can tilt their bodies mouth down more easily this way.
  - krisoft 5y ago
    Yes. What you are talking about is a fish keeping a fixed depth. Having a swim bladder enables the fish to attain neutral buoyancy. That way the fish doesn't need to expand energy to keep itself from sinking or floating up. What the article is talking about is position keeping against the current in flowing water. Swim bladder is good for up-down position keeping, the article's phenomenon is good for forward-backward position keeping. Interestingly there is a way to use a swim bladder like construct to propel one forward. Underwater gliders do this, and the process is very energy efficient. The way it works is that the glider uses its variable buoyancy device (an artificial swim bladder) to set a negative buoyancy and starts sinking. The wings of the glider turn this downward motion into forward speed. At the target depth the glider expands some energy from its batteries to set a positive buoyancy and keeps the forward momentum as it is ascending. Because of this they only need to use energy at two points (at the top and the bottom) in their saw-tooth like swim profile, and they can travel thousands of kilometers on a single charge. https://en.wikipedia.org/wiki/Underwater_glider https://en.wikipedia.org/wiki/Underwater_glider

NAR8789 5y ago

The fish is not merely holding position--it's actually accelerating upstream! Reminds me of this Tadashi video: [How do fish swim so quickly?] https://www.youtube.com/watch?v=wYDh5d9pfu8 https://www.youtube.com/watch?v=wYDh5d9pfu8 Tadashi shows that fish turn drag into thrust by swapping the positions of the vortices they shed. Low effort, high output. TFA takes this one step further--fish bodies are shaped to effortlessly harvest thrust from drag. No effort, free energy!

a3w 5y ago
TIL: The first law of thermodynamics has an exception for dead fish. (JK, don't cite me in physics class!)
- munificent 5y ago
  Well, actually... In this case, the fish isn't a closed system. It's harvesting energy from the moving water, which requires external energy from the sun to keep the water cycle going.
- bocytron 5y ago
  Reminds me of Derek's video about a vehicle which is powered against wind: https://youtube.com/watch?v=jyQwgBAaBag https://youtube.com/watch?v=jyQwgBAaBag
  - Maursault 5y ago
    His claim about a sailboat not being able to exceed windspeed sailing directly downwind is deceiving because it is definitely not the fastest point of sail. I believe this is done for dramatic effect to make Blackbird's feat sound more incredible. Sailing close hauled, almost directly into the wind, can achieve double wind speeds near effortlessly on low draft racing multihulls, and possibly on land with whatever those sailing carts are called. Of course, directly downwind is the only course for this experimental propellor craft, thus the only criteria.
    - 5y ago

kuhewa 5y ago

Besides energy saving behaviour, the metabolic rate has been depressed due to the physicochemical effects of cold, typically a reduction of 2-3x per 10 degrees. In terms of having enough energy, energy stores accrued during summer and autumn go a long way, but many fish are indeed a negative energy flux state over winter. In fact, over-winter starvation in the first year or three is a common ecological bottleneck, where even if fish are capable of reproducing and adults are fine and can survive the first year, the 0+ age class may not have had sufficient time to store enough energy before winter to survive until spring.

scoot 5y ago

> That fish looks alive until you know it isn’t. Schrodinger's fish.