Light diffraction by sarcomeres produces iridescence in transmission in the transparent ghost catfish

摘要

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).

范秀君

Master

安童

PhD

赵其斌

副教授

研究兴趣包括胶体光子晶体组装、材料结构规则度调控、规则及不规则结构在不同条件下的演变过程及物理机理、光学材料及能源类材料制备、微纳结构材料的大面积制备方法、自然界中的功能结构及其在跨种演变视角下的生物进化学等。