Scientists have found that hogfish are equipped with an exceptional light-sensitive protein in their skin that allows them to alter their color. This discovery implies that the fish have the capability to be cognizant of shifts in their own skin color, which might, in turn, facilitate better environmental adaptation.
Several years ago, during a marine excursion in the Florida Keys, biologist Lori Schweikert had a firsthand encounter with an extraordinary transformation. After capturing a hogfish—a species of pointy-snouted reef fish—Schweikert placed it on the deck of her boat. When she later sought to move it to a cooling container, she noticed a striking event: the fish’s skin had assumed the same hue and pattern as the boat’s deck.
The hogfish, a species native to the western Atlantic Ocean ranging from North Carolina to Brazil, has long been recognized for its color-changing capabilities. The fish can swiftly transition from white to variegated to reddish-brown in order to blend in with their surroundings, such as corals, sand, or rocks.
What caught Schweikert’s attention was that this particular hogfish maintained its camouflage even post-mortem. This prompted her to question if hogfish could perceive light solely through their skin, without relying on their eyes or central nervous system.
This inquiry led Schweikert into extensive research on the subject of “skin vision,” which she pursued as a postdoctoral fellow at both Duke University and Florida International University. In 2018, a study was published by Schweikert in collaboration with Duke biologist Sönke Johnsen, which identified a gene in hogfish that codes for a particular light-sensitive protein known as opsin. This protein is activated in the fish’s skin and is distinct from the opsin genes found in their eyes.
Other animals known for their color-changing abilities—ranging from octopuses to geckos—also possess light-sensitive opsins in their skin, although the exact function remains undefined.
New findings propose another potential utility for light-sensitive skin, suggesting it might serve to enable animals to perceive their own appearance, according to Schweikert. Further research involved microscopic imaging of skin samples from different areas of the hogfish’s body. These specialized cells, known as chromatophores, contain pigment granules capable of varying color through spreading or clustering together.
Additional experiments utilized immunolabeling to identify the location of opsin proteins within the skin cells. Contrary to expectation, opsins were not produced in the chromatophores but were present in adjacent cells. Electron microscopic images exposed a hitherto unidentified cell type filled with opsin proteins located directly beneath the chromatophores.
Preliminary findings suggest that the opsins in hogfish skin are most responsive to blue light, which also aligns with the wavelength most effectively absorbed by the pigment granules in the chromatophores. This insight implies that these light-sensitive proteins operate akin to an internal photodetector, capturing alterations in light as it filters through pigment-filled cells above.
While the research clarifies that the function of hogfish skin is not analogous to an eye, it does offer a feedback mechanism that enables the fish to adjust its own skin color based on what it perceives.
This body of research holds broader implications for technological innovations such as robotic limbs and autonomous vehicles, which may benefit from new forms of sensory feedback systems.
The study was a collaborative effort involving scholars from the Florida Institute of Technology, Florida International University, and the Air Force Research Laboratory. Financial backing was provided by Duke University, Florida International University, the Marine Biological Laboratory, and the National Science Foundation. The findings were published in the journal Nature Communications on August 22, 2023.
