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Fishy physics: Adaptation lets silvery fish reflect light without polarization, may help them evade predators

Date:
October 21, 2012
Source:
University of Bristol
Summary:
Silvery fish such as herring, sardine and sprat have evolved special skin that gets around a basic law of physics, according to new research. Reflective surfaces polarize light, a phenomenon that fishermen or photographers overcome by using polarizing sunglasses or polarizing filters to cut our reflective glare. However, researchers found that these silvery fish have overcome this basic law of reflection -- an adaptation that may help them evade predators.

Herring. The skin of sardines and herring contain not one but two types of guanine crystal -- each with different optical properties. By mixing these two types, the fish's skin doesn't polarize the reflected light and maintains its high reflectivity.
Credit: dbvirago / Fotolia

Silvery fish such as herring, sardine and sprat have evolved special skin that gets around a basic law of physics, according to new research from the University of Bristol published Oct. 21 in Nature Photonics.

Reflective surfaces polarize light, a phenomenon that fishermen or photographers overcome by using polarizing sunglasses or polarizing filters to cut our reflective glare. However, PhD student Tom Jordan and his supervisors Professor Julian Partridge and Dr Nicholas Roberts in Bristol's School of Biological Sciences found that these silvery fish have overcome this basic law of reflection -- an adaptation that may help them evade predators.

Previously, it was thought that the fish's skin -- which contains "multilayer" arrangements of reflective guanine crystals -- would fully polarize light when reflected. As the light becomes polarized, there should be a drop in reflectivity.

The Bristol researchers found that the skin of sardines and herring contain not one but two types of guanine crystal -- each with different optical properties. By mixing these two types, the fish's skin doesn't polarize the reflected light and maintains its high reflectivity.

Dr Roberts said: "We believe these species of fish have evolved this particular multilayer structure to help conceal them from predators, such as dolphin and tuna. These fish have found a way to maximize their reflectivity over all angles they are viewed from. This helps the fish best match the light environment of the open ocean, making them less likely to be seen."

As a result of this ability, the skin of silvery fish could hold the key to better optical devices. Tom Jordan said: "Many modern day optical devices such as LED lights and low loss optical fibres use these non-polarizing types of reflectors to improve efficiency. However, these human-made reflectors currently require the use of materials with specific optical properties that are not always ideal. The mechanism that has evolved in fish overcomes this current design limitation and provides a new way to manufacture these non-polarizing reflectors."


Story Source:

The above story is based on materials provided by University of Bristol. Note: Materials may be edited for content and length.


Journal Reference:

  1. T. M. Jordan, J. C. Partridge, N. W. Roberts. Non-polarizing broadband multilayer reflectors in fish. Nature Photonics, 2012; DOI: 10.1038/nphoton.2012.260

Cite This Page:

University of Bristol. "Fishy physics: Adaptation lets silvery fish reflect light without polarization, may help them evade predators." ScienceDaily. ScienceDaily, 21 October 2012. <www.sciencedaily.com/releases/2012/10/121021133911.htm>.
University of Bristol. (2012, October 21). Fishy physics: Adaptation lets silvery fish reflect light without polarization, may help them evade predators. ScienceDaily. Retrieved August 30, 2014 from www.sciencedaily.com/releases/2012/10/121021133911.htm
University of Bristol. "Fishy physics: Adaptation lets silvery fish reflect light without polarization, may help them evade predators." ScienceDaily. www.sciencedaily.com/releases/2012/10/121021133911.htm (accessed August 30, 2014).

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