Flashing spots on the dorsal trunk of hardyhead silverside fish.

A large number of living creatures are able to use ambient light effectively in biological signalling. , a teleost fish has alignments of circular spots on its dorsal trunk. The spot consists of iridophores, whose diameters are approximately 7-10 µm. The iridophore contains guanine crystals with diameters of 1-3 µm. Here, it is found that more than one spot with a diameter of approximately 0.1 mm causes a rhythmic flashing of light when viewed under white light. The typical light flash has a pulse width of approximately one second. When a pulsed train of flashes appears, the flash repeats at a typical frequency of 0.5-1 Hz. The observed phenomenon is one example of the evidence for the existence of rapid colour changing teleost fish.