Sardine link to optical devices

Sardines and other silvery fish whose bodies reflect light may offer scientists useful tips on designing optical devices.

Crystals in the skin of the fish prevent light reflected from their surfaces from becoming polarised, which would ruin their camouflage.

Fish such as sardines and herring possess not one but two types of the “guanine” crystals, researchers have discovered.

Each crystal has different optical properties. By mixing them together, the fish ensure that light bouncing off their skin is not polarised and they remain highly reflective.

This helps them hide from predators by matching the background light flickering through the water.

Dr Nicholas Roberts, from the University of Bristol, said: “We believe these species of fish have evolved this particular multi-layer structure to help conceal them from predators, such as dolphin and tuna.

“These fish have found a way to maximise 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.”

The findings are published in the journal Nature Photonics.

Co-author Tom Jordan said: “Many modern day optical devices such as LED lights and low-loss optical fibres use these non-polarising types of reflectors to improve efficiency.

“However, these man-made reflectors currently require the use of materials with specific optical properties that are not always ideal.”