WILMINGTON, N.C. — A unique species of fish possesses the remarkable ability to “see” using its skin, according to a new study. This groundbreaking revelation came to light when Dr. Lori Schweikert, a biologist, observed an unexpected phenomenon during a fishing excursion in the Florida Keys.
She caught a hogfish, a species known for its rapid color-changing abilities, and set it on her boat’s deck. Later, when Dr. Schweikert intended to transfer the fish to a cooler, she was stunned to find its skin had assumed the color and pattern of the boat’s deck.
Though the hogfish, commonly found in the western Atlantic Ocean from North Carolina to Brazil, is renowned for its color-changing capacities, Dr. Schweikert was surprised. The hogfish she caught continued its camouflage, despite being deceased. This observation led her to ponder whether the species might have the capability to perceive light solely through their skin, independent of their eyes and brain.
Subsequently, during her tenure as a postdoctoral fellow at Duke University and Florida International University, she delved deeper into the concept of “skin vision.” In 2018, in collaboration with Duke University biologist Professor Sönke Johnsen, she published a study revealing that hogfish possess a gene for a light-sensitive protein called opsin, which becomes activated within their skin. Intriguingly, this gene differs from the opsin genes in their eyes. This light-sensing ability in the skin is not unique to hogfish; other color-changing creatures like octopuses and geckos also have similar capabilities.
“When we found it in hogfish, I looked at Sönke and said: Why have a light detector in the skin?,” recounts Dr. Schweikert, currently an Assistant Professor at the University of North Carolina Wilmington (UNCW), in a media release.
One theory suggests that light-sensing skin aids animals in perceiving their environment.
“They could be using it to view themselves,” adds Dr. Schweikert.
In further research, the team took a microscopic view of hogfish skin and found it resembled a “pointillist” painting, each color dot being a specialized cell known as a chromatophore. These chromatophores contain pigment granules of varied colors, which alter the skin’s hue based on their movement.
Using immunolabeling, the team located the opsin proteins in the skin. Unlike initial assumptions, the opsins were found not in the color-changing chromatophore cells but in a layer beneath them. Electron microscope images even revealed a previously unidentified cell type rich in opsin protein.
Further analysis suggests that the light-sensitive opsins in the hogfish skin are most responsive to blue light, which coincidentally is the primary wavelength absorbed by the fish’s chromatophores. These findings propose that the light-sensitive opsins function similarly to internal Polaroid film, registering light changes as the pigmented cells above rearrange.
“Just to be clear, we’re not arguing that hogfish skin functions like an eye. Eyes do more than merely detect light — they form images. We don’t have any evidence to suggest that’s what’s happening in their skin,” says Dr. Schweikert. “It seems they are watching their own color transition.”
This pioneering research holds potential for future applications. The study could inspire innovative sensory feedback methods for technologies such as robotic limbs and autonomous vehicles, which need to fine-tune their operations without exclusively relying on vision or camera inputs.
“Imagine not having a mirror or the flexibility to view yourself. How would you ascertain if you’re appropriately attired? For us, it might be inconsequential. But for species that use color-shifting as a survival tool, it can mean the difference between life and death,” concludes Dr. Schweikert.
The study is published in the journal Nature Communications.
South West News Service writer Stephen Beech contributed to this report.