Iridescence in glass catfish

[Silurus]

Fan, X-J, X-Z Zheng, T An, X-H Li, N Leung, B Zhu, T Sui, N Shi, T-X Fan & Q-B Zhao, 2023. Light diffraction by sarcomeres produces iridescence in transmission in the transparent ghost catfish. Proceedings of the National Academy of Sciences of the United States of America 120: e2219300120.

Abstract

Despite the elaborate varieties of iridescent colors in biological species, most of them are reflective. Here we show the rainbow-like structural colors found in the ghost catfish (Kryptopterus vitreolus), which exist only in transmission. The fish shows flickering iridescence throughout the transparent body. The iridescence originates from the collective diffraction of light after passing through the periodic band structures of the sarcomeres inside the tightly stacked myofibril sheets, and the muscle fibers thus work as transmission gratings. The length of the sarcomeres varies from ~1 μm from the body neutral plane near the skeleton to ~2 μm next to the skin, and the iridescence of a live fish mainly results from the longer sarcomeres. The length of the sarcomere changes by ~80 nm as it relaxes and contracts, and the fish shows a quickly blinking dynamic diffraction pattern as it swims. While similar diffraction colors are also observed in thin slices of muscles from non-transparent species such as the white crucian carps, a transparent skin is required indeed to have such iridescence in live species. The ghost catfish skin is of a plywood structure of collagen fibrils, which allows more than 90% of the incident light to pass directly into the muscles and the diffracted light to exit the body. Our findings could also potentially explain the iridescence in other transparent aquatic species, including the eel larvae (Leptocephalus) and the icefishes (Salangidae).

[Viktor Jarikov]

Fascinating. Thank you.

[Silurus]

I was interviewed for the story reporting this paper (when I wasn't even involved in it) at https://www.sciencenews.org/article/tra ... iridescent. Guess they didn't want to interview the physicist authors because biologists know how to keep it real.

[bekateen]

Interviewing an uninvolved scientist is a common practice when reporting on scientific findings. I don't know why.

No matter, you're famous! What's next? Social influencer?

Cheers, Eric

[Jools]

#aquaticicon

Jools

[Viktor Jarikov]

Obviously, physicists and chemists et al need to go to fish stores more often.