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Started by Recusant, March 13, 2023, 10:47:31 PM
QuoteImage Credit: Nan Shi, Xiujun Fan, and Genbao WuThe ghost catfish, endemic to Thailand, is [a fish] that loves to show off its dazzling array of colors. That might come as a surprise at first glance: the fish is almost completely transparent. When the light strikes it just right, though, the creature seems to glow with all the colors of the rainbow.In a study published on Monday in the journal Proceedings of the National Academy of Sciences, researchers found out why exactly this happens. Using a combination of X-rays, laser lights, and electron microscopy, the study's authors were able to find distinct optical properties in the fish's skin and muscle that allow it to cast the dazzling array of light.[Continues . . .]
QuoteAbstract: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).
QuoteKryptopterus species are different from most other catfish because they are free-swimming and live in the mid to upper region of the water. Ghost catfish commonly favor dark places to being out in the open light. A small school of them may hide under elevated rocks, logs, or the shadow of plants. Sometimes, however, one or two may venture out into the open and swim in the upper level of the water. They can be enticed to do this more often if the flow of water in the tank is arranged so that their favorite hiding spots are sheltered, while a gentle current flows in the open areas. Thus, they will move in the open especially at feeding time, as they like to go after food drifting in the current. A generous growth of aquatic plants is necessary for their well-being, and floating plants can filter bright light, which they seem to find unpleasant.