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Ghost Catfish, With Rainbow Spectrum

Started by Recusant, March 13, 2023, 10:47:31 PM

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Intriguing visuals, and an interesting explanation.

"Watch This Ghost Catfish Glow with Dazzling Rainbows" | The Daily Beast


Image Credit: Nan Shi, Xiujun Fan, and Genbao Wu

The 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 . . .]

The paper is behind a paywall.


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).

"Religion is fundamentally opposed to everything I hold in veneration — courage, clear thinking, honesty, fairness, and above all, love of the truth."
— H. L. Mencken

Dark Lightning

Cool! I'm guessing that that is the sun, above it? Or maybe a man-made light? I'm amazed that these fish haven't all been eaten, what with the flashing billboard, "Eat Me!"  :)


Seems like an LED light to me, shining directly athwart the fish. From a different angle, it looks like they can appear as a little sliver (per illustration below from the article). Still enticing, but a smaller target? I went to the Wikipedia article and found this, which tells us that the fish in that GIF are not particularly comfortable--and I think is also telling in regard to your comment Dark Lightning:

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.

Image Credit: Nan Shi, Xiujun Fan, and Genbao Wu
"Religion is fundamentally opposed to everything I hold in veneration — courage, clear thinking, honesty, fairness, and above all, love of the truth."
— H. L. Mencken

Dark Lightning

Makes sense. I can't imagine a fish like that living long in bright light.


I wonder if there aren't some sort of venomous creatures that exhibit similar iridescent colors in their native habitat. A jellyfish or similar. That type of display could be useful for a column feeder that typically hides in structure. Predator species would see the flash of light and assume that it's inedible unless they saw them up close and could recognize them as baitfish.

Barring that, translucency could be beneficial on its own. Despite the vast menu of options for lures, the most effective are - from a statistical perspective - solid black. Black lures give a silhouette that predators can key in on in nearly any lighting conditions.

Translucent baitfish might be confusing to predators who are conditioned to target silhouettes based on their actions in the water, even if we find their color patterns in the sun visually striking. A small target could use this confusion to quickly dart out, feed in the flow, and then dart back to relative safety.

I'm somewhat ashamed of the amount of money I've spent on tackle that closely mimics real fish when I know damn well how much more effective solid black soft plastic is likely to be.

"Amazing what chimney sweeping can teach us, no? Keep your fire hot and
your flue clean."  - Ecurb Noselrub

"I'd be incensed by your impudence were I not so impressed by your memory." - Siz

Dark Lightning

Well, shit. All that dynamite gone to waste. My FiL caught fish wherever he went. Annoying, because I and everyone around him got skunked, a lot.

No one

It's was an evolutionary advandage, until the emergence of the ghost-busting dogfish.