Silver Fish Overcome Basic Law of Reflection

It is known that the skin of the fish contains multi layer arrangements of reflective guanine crystals. These are responsible for polarizing light when reflected. 

But the latest Bristol study that focuses on silvery fish such as herring, sardine and sprat state that their skin contains two types of guanine crystals each with different optical properties.

This special skin gets around the basic law of physics. Combination of two types of guanine crystals the fish's skin doesn't polarize the reflected light and maintains its high reflectivity.

Reflective surfaces polarize light, a phenomenon that fishermen or photographers overcome by using polarizing sunglasses or polarizing filters to cut our reflective glare. 

But according to the research that is being conducted by  PhD student Tom Jordan and his supervisors Professor Julian Partridge and Dr Nicholas Roberts in Bristol's School of Biological Sciences,  silvery fish have overcome this basic law of reflection an adaptation that may help them evade predators.

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."

This study was published in Nature Photonics.