Polarized vision

[wet]

Why Fish Have 'Sunglasses Sight' |Sky News|Strange News

I don't quite understand what they mean, polarized vision used by goldfish to hunt? I thought goldfish were primarily vegetarians (grass carp?)
Invertebrates have polarized vision?

I thought polarized vision didn't work under water, only above water looking through the reflection.

[Pastor]

I have seen goldfish eating their young in the fish pond. Lucia?

Polaroid lenses will work anywhere singly, it never occurred to me before but they would be ideal in the shallows where sunlight reflects off all the sediment in the water reducing the view to a bright glare. it would be interesting to compare them with amber lenses

[sanso]

Originally Posted by wet

... Invertebrates have polarized vision? ..
I thought polarized vision didn't work under water, only above water looking through the reflection.

Okay, for invertebrates having polarized vision, yes, some do. For example bees use polarized vision to be able to locate the sun even under cloudy skies and thus be able to navigate accordingly.
Goldfish are vertebrates, though. (They have vertebrae )

As for having an effect under water: Polarized vision will have an effect wherever there is polarized light to be seen, which can be anywhere. The thing with polarized lenses for (above-)water sports is just that a portion of the light, when reflected especially at a low angle (e.g. by the surface of the water) becomes polarized, so a polarized lens allows one to selectively filter out the glare from the water. So the overall amount of light available is still relatively high, but the glare is gone.
This is also why, with polarized lenses, it's easier to look through windows in daylight: The reflected images on the window pane get filtered out and only the light coming through the window is left.

phew!...

Wow! This must be about the third time that physics 101 has helped me in real life!

[Pastor]

Will you explain the wave/particle duality of light to me, I never could get a grip on that

I did a little work with polarised light with an ill based experiment a couple of years ago. Polarised lenses are made up of loads and loads of tiny parallel lines a few tinyweenymetres apart. Normal light is made up of waves whose up and down direction is non standard. Only waves which line up with the lines on the lens are allowed to pass through and those that do are now polarised. The diagram explains it better

[trux]

Originally Posted by Pastor

Will you explain the wave/particle duality of light to me, I never could get a grip on that

That's relatively easy. Light has in the same time properties of a wave (like for example an electromagnetic wave), and in the same time properties of a particle (like for example an electron). Einstein's Special Theory of Relativity explains why. Even if you are not a physicist, you probably know that objects moving with the speed close to the speed of light are changing their weight and length. Better told, they just appear to be lighter and longer to the static observer, but should you be moving with the same speed as the object, it will have the same length and weight as you are used to (from your standpoint). So in fact, very simplified told, it is somehow just a kind of a "visual effect" - similar to fast moving objects in cartoons - they are being designed prolonged too .

Now, the photons move with the maximal possible (measurable) speed (the speed of light) - hence due to the above mentioned principle, they are (better told, appear to be) extremely long (imagine them as very long strings), and endlessly light (weightless). So from this point of view they have most features of a wave that transfers no particles, no matter. But then, when you manage to slow down the light by passing through material or by reflexions, the photons show their real face, and you observe their particle properties - for example light is able to mechanically move a light mill, similarly as a beam of material particles - you certainly saw it in the school too.

The light/photon hence behave in the same time as a wave and as a particle - in contrary to (for example) the electromagnetic wave and electron - unlike at light where photons move from one point to another, electrons are not being transported at electromagnetic radiation (though they interact with it).

These principles are perfectly demonstrated in Photonic Laser Propulsion: imagine a spacecraft turning on a massive laser. Normally, nothing would happen - the spacecraft would not gain any speed, just because the photons shooting out have no weight. But using a simple trick - slowing down the photons slightly through millions of reflexions in the reactive chamber, they gain some weight and when they then finally shoot out of the space craft, they push it in the opposite way, and hence can accelerate it to a great speed. The BAE Institute demonstrated a small laser propulsion in their laboratory - with a stock laser they managed to generate thrust of 35 µN - that seems tiny, but if scaled up, it could thrust a space craft to Mars in about a week (instead of many months we currently need for it).

Erratum: as pointed out by other further below in this thread - what I wrote above about the weight is complete nonsense and in fact it is exactly the opposite case. Sorry for the confusion, next time I should first dust off my school knowledge before posting. I should better remove or correct the text above, but since it was already quoted below, I am keeping it here for reference as a wisdom of my stupidity.

PS: the laser thruster is for real though

[bdurrett]

It is nice to see another Rocket Scientist in the fold!

(I am a consultant for ESA when I am not engaging in real life activities like diving.....)

[naiad]

Goldfish expert reporting for duty.

Originally Posted by wet

I don't quite understand what they mean, polarized vision used by goldfish to hunt? I thought goldfish were primarily vegetarians (grass carp?)

I thought polarized vision didn't work under water, only above water looking through the reflection.

Goldfish will eat a wide range of foods, including algae, plants, invertebrates, fish eggs and small fish.

Many books and websites say that the goldfish is a domesticated form of the carp. This is incorrect. They are different species, and both have been domesticated separately. Some goldfish and carp may look almost identical, but the carp (Cyprinus carpio) grows much larger and has barbels, unlike the goldfish (Carassius auratus).

The grass carp is yet another species, with the impressive Latin name of Ctenopharyngodon idella. It feeds mostly on plants and algae.

I don't know how polarized vision would help them, maybe to see insects which have landed on the surface, or to spot predators above the surface?

Although the goldfish and carp are mostly bottom-feeders, some related fish are surface and midwater feeders, such as the Orfe. If they also have polarized vision, they may benefit more from it. They hunt mostly by sight, and feed on plankton, surface insects and small fish. The goldfish and carp use a combination of sight, smell and random 'vacuum-cleaning'.

Originally Posted by Pastor

I have seen goldfish eating their young in the fish pond. Lucia?

They will often eat their eggs and young if given the chance. Once the young are past the transparent fry stage and look like small fish, they are less likely to be eaten. In a pond with lots of plants and other hiding places, some will survive. It is often better that only a few survive, as they produce thousands of eggs, and overcrowding will produce stunted fish.

On the subject of grass carp, they are often sold for algae control. They do eat blanketweed algae in the wild, but in captivity they will eat almost anything else to avoid it. If given a choice of foods, they prefer to eat commercial carp food, invertebrates and small fish. If these are not available they will turn to plants, eating first the leafy ones and then the tough ones such as waterlily stems. Only if none of these is available will they start to eat the blanketweed. It must taste as bad as it looks.

[Pastor]

Physics, rocket science and now latin names? Too much, far too much for one day. I'm going for a lie down

[wet]

i am humbled. (don't worry, after lunch, i'll be back to normal.)

Still can't figure out what it has to do with the north pole... Eskimos wearing those "polarised" narrow-slit wooden "sunglasses" to prevent snow blindness? Is that where the name is from?

thanks much for the expertises!

DDeden

[sanso]

Originally Posted by wet

..Still can't figure out what it has to do with the north pole... Eskimos wearing those "polarised" narrow-slit wooden "sunglasses" to prevent snow blindness? Is that where the name is from?
...

All those slit glasses do is reduce the amount of light that hits the eye in order to prevent snow-blindness. They do not however polarize light. The problem with snow is that it reflects light very well, so without protection, Your eyes get a massive photon blast, way more than is good for them. - Hence the cool sunglasses and the ski/snowboarder-tan.

[BatRay]

Polarization seems to result in an exaggerated difference between different light sources. This would help a predator to distinguish between two object of similar color that have subtle differences. They may be capable of recognizing that one color means food and the other does not. In general, animals have a much wider range of color vision than humans. That makes me feel cheated.

[naiad]

Originally Posted by BatRay

In general, animals have a much wider range of color vision than humans. That makes me feel cheated.

The goldfish is a masterpiece of nature. It has many abilities which could come in useful, and it doesn't have a 3 second memory. Maybe being a goldfish is not so bad.

- It can see a full range of colours, unlike many other vertebrates and most mammals. It also has a very large field of vision, including above the surface.

- It can navigate in the dark by using its lateral line to detect objects.

- It can clone itself - some populations of wild goldfish are all-female and produce identical female offspring.

- Its hypoxic tolerance is very high, so it can live in stagnant water. It is closely related to the crucian carp.

- Unlike most animals, goldfish and some other coldwater fish can function normally with a wide range of body temperatures. I have seen them still reasonably active at 3c and 30c.

- There are more breeds of goldfish than any other fish, and it is thought to be the first to be domesticated. I don't envy them for that, as features include raspberry-like head growths and protruding eyes.

- The ones in pet shops and fairgrounds are not fully grown - they can easily reach 20cm and 1lb, and sometimes a lot more.

- They have 8 teeth, which can only be used for chewing and not biting. The teeth are replaced as they wear out.

- The goldfish is not meant to be orange. Despite its common and latin names describing it as golden, it was originally bronze or brown. Orange ones were specially bred. They are supposed to be unable to survive in the wild, but probably because of the above reasons, they seem to manage very well despite their colour.

[BatRay]

I've had some that stayed brown for a long time, then slowly changed to orange. Usually, the brown concentrates and recedes until it is limited to the tips of the fins and a very funny moustache. That goes away too. Mine also grow quite large. I recently lost a fantail whose body was larger than a golf ball. It was a very sad loss.

Say, Lucia, would you happen to know if goldfish can get bubbles in their fins? Mine seem to have that problem.

[naiad]

Most goldfish start off brown. They may change colour after a few weeks or several years. Some remain brown for the rest of their life.

Sorry about your fantail. I lost a beautiful Calico Lionhead a few months ago.

I now have 10 goldfish. 9 of them were unwanted pets, probably because they have grown too big. Some are still growing, I don't know what to do!

They can get bubbles in their fins. I explained how that happens here. If the excess plants or algae are removed, the bubbles should disappear soon. Are your fish indoors or outdoors?

[BatRay]

They are indoor fish. Their tank became quite dirty awhile back, but I did a 90% water change and fixed it. Their tank does not have any plants, but it does seem to have algae overgrowth. I'm thinking about switching them to a tank with less algae, and switching my pleco to the algae-filled tank. That sound ok?