This Incredible Color-Changing Fish Can 'See' With Its Skin

Amazing stuff! How does a color changing fish, which adopts to the environment, know its current colors?

"... To do this the hogfish rely on pigment filled cells called chromatophores, like other animals that use dynamic skin color from octopus to chameleons.

Pigments within these cells huddle close together to allow the white flesh below to shine through. But as various combinations of the red, yellow or black pigments spread out, the surface level cells transform in hue and shade. ...
Research on another fish, the Nile tilapia (Oreochromis niloticus), found light sensitive molecules called opsins can influence chromatophore color. ...

They tracked down the opsin molecules to cells directly beneath the fish's chromatophores. These newly discovered opsin-producing cells are most sensitive to the short, blue wavelengths that can pass through the chromatophores. What's more, the light levels vary the amount of opsin released. ..."

From the abstract:

"Dynamic color change has evolved multiple times, with a physiological basis that has been repeatedly linked to dermal photoreception via the study of excised skin preparations. Despite the widespread prevalence of dermal photoreception, both its physiology and its function in regulating color change remain poorly understood. By examining the morphology, physiology, and optics of dermal photoreception in hogfish (Lachnolaimus maximus), we describe a cellular mechanism in which chromatophore pigment activity (i.e., dispersion and aggregation) alters the transmitted light striking SWS1 receptors in the skin. When dispersed, chromatophore pigment selectively absorbs the short-wavelength light required to activate the skin’s SWS1 opsin, which we localized to a morphologically specialized population of putative dermal photoreceptors. As SWS1 is nested beneath chromatophores and thus subject to light changes from pigment activity, one possible function of dermal photoreception in hogfish is to monitor chromatophores to detect information about color change performance. This framework of sensory feedback provides insight into the significance of dermal photoreception among color-changing animals."

This Incredible Color-Changing Fish Can 'See' With Its Skin : ScienceAlert As if changing color isn't impressive enough, hogfish can 'see' with their skin too. A new US study suggests this bizarre form of visualization is how the reef fish detect their own colors.

Dynamic light filtering over dermal opsin as a sensory feedback system in fish color change (open access)

Fig. 1: Dynamic color change of hogfish (Lachnolaimus maximus).