Science News

How a Fish broke the Laws of Physics

Sun, 21st Oct 2012

Ginny Smith

Part of the show Flashy Fish and A Vaccine for Herpes

A group of researchers from Bristol University have discovered that the optical properties of a fish’s skin seem be more reflective than was previously thought possible for a non- metallic object.

SardinesNormally when light is reflected, from snow, or the sea for example, it becomes polarised. This means that the light is reflected only in the direction parallel to the reflective surface, producing the familiar ‘glare’. This glare can be reduced by wearing polarized sunglasses.

Fish such as sardines and herring have skin made up of several layers. Underneath the scales is a layer which contains arrangements of reflective ‘guanine’ crystals. It was thought that, like other reflective objects, these fish would polarise light, producing a drop in reflectivity. The team found, however, that two different types of guanine crystal are present in the fish’s skin. Each of these reflects light in a direction at 90 degrees to the other. This, combined with the fact that the fish has multiple layers of these crystals, means that whatever direction the light comes in at, it is always reflected, so there is no polarisation.

The fish in this study, published in Nature Photonics are all prey animals, so it is thought that reflecting the surrounding light levels gives them some camouflage in the water. The depth of water they live in has a very symmetrical distribution of light, so ensuring they are reflective from all angles gives them a lower chance of being spotted by predators such as tuna or dolphins.

Multi-layer reflective materials are common in things like optical fibres and LED back reflectors, and producing a reflector that does not polarise light can be fundamentally important. These finding may help us produce better reflectors, from a wider range of materials.



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Bumble bees fly without defying the laws of physics. We just didn't understand the laws of physics.

Apparently, there's still a lot we don't understand about optics. Perhaps the scales use total internal reflection to turn the light around. We should study the internal structure of individual scales.

Fish scales hold dazzling secret

Phractality, Sun, 21st Oct 2012

Is a reflective fish skin actually a good source of camouflage?  That seems somewhat counter-intuitive, especially when I've seen videos of schools of brightly colored fish.  Perhaps it all depends on the amount of light, depth of water, background, and etc. 

Could nature have evolved highly reflective scales as a form of population control?

CliffordK, Mon, 22nd Oct 2012

Most fish are dark on top, so they look like the deep water below, and bright on the bottom, so they look like the sky above. It's difficult to look as bright as the sky when you are illuminate by the dark water below. You have to rely on light from the side and reflect it downward. Phractality, Mon, 22nd Oct 2012

"Bumble bees fly without defying the laws of physics. We just didn't understand the laws of physics."

There is a myth that states scientists show that bumble bees can't fly. This isn't quite true. If you read the original paper it states bumble bees can't GLIDE. Not quite the same thing. The smaller an animal is, the harder it is for that animal to glide, that is, hold it's wings out and fly without adding thrust.

You can see this with birds. Large birds like eagles and buzzards usually glide. They user thermals as much as possible and flap their wings only when they have too. Small birds link finches never, if ever glide. There is a bird here in the PNW that never glides. He'll flap his wings a few times then fold them and coast a few seconds then flap again before he gets too low.

Bumble bees, being much smaller than even the smallest birds can't glide at all. But they have no trouble at all flying. krool1969, Tue, 23rd Oct 2012 gives a better explanation. Actually, we didn't understand the aerodynamics of bumblebee flight until our computers were able to simulate it. The key is the formation of vortices above the trailing edge of the wing as it swings forward and back. If not for the extra lift generated by the vortices, the bumble would not be able to fly. Phractality, Tue, 23rd Oct 2012

"How do fish defy the laws of physics?"

They don't.  :) jpetruccelli, Tue, 23rd Oct 2012

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