Physical mechanism for the extremely rapid twinkling by chromatophores of Atherinidae

Lymphatics and secondary circulation systems of teleost exist in the skin layer where chromatophore cells coexist. This work reveals that in the skin of three species of Atherinidae, an extremely rapid flashing iridophore acts as fluid pressure sensor and visualizes micro-circulations in the layer. The fish has a capillary network propagating fluid pressure from the primal circulation systems. Complex of xanthophore, iridophore and micro-circulation network forms the twinkling spot that change light reflection intensity in 100 ms. The movement of light reflecting particles of iridophore, to which fluid pressure is applied, is the mechanism of twinkling skin tissue. The iridophores form a membrane with honeycomb compartments containing guanine platelets. Micro-circulation capillaries are embedded in the honeycomb membrane and provide driven forces for the light reflecting platelet movements. Two dimensional image of the micro-citculation appears on the twinkling patterns. The results suggest that real-time visualization of the micro-circulations can be achieved in the body of the Atherinidae. Making mimicry of the native skin device with the twinkling iridophores can contribute to developing the new artificial skin device for visualizing lymphatic micro-circulation system that can monitor an immune process in real time.