Sailfish can change their colours almost instantly. The color change confuses its prey and making capture easier, while signaling its intentions to fellow sailfish.
They can appear in an array of colors, from subdued browns and grays to vibrant purples and even silver. Their body colors are often highlighted by stripes of iridescent blue and silver dots. Nerves send signals to specialized cells called chromatophores and iridophores. Chromatophores contain pigment, and there are several kinds, including melanophores, which contain the black or brown pigment melanin. Below the melanophores lie iridophores, which produce color structurally rather than with pigment. These cells have layers that reflect light; creating iridescent colors such as metallic blue and silver. The sailfish appear dark when the pigment inside the melanophores is evenly distributed across the cells.
Scale from silver dollar fish, with contracted guanophores and single-spread melanophore (1000x)
A melanophore is a chromatophore, dark pigment-containing cell in the deeper layers of the skin of animals. The distribution of the chromatophores and the pigments they contain determine the colour patterns of an organism.