Is there any fish that will turn white if left in a dark room?

Answer 1

I am not familiar with any specific species of fish that will do this. If there are fish that do this, hopefully someone else can give you some names.

However, I can tell you something of the mechanism behind fish turning colors since I did experiments on this in high school. And by "fish" I assume you are referring only to higher vertebrate aquatic life and not octopus or other sea creatures who have this amazing ability to change colors; my experiments were on goldfish and their color range and the mechanism behind it.

First some simplified color chemistry. There are 2 basic kinds of color: pigment color (like paint) and light color (like the sun.) While white light (color) is made from ALL the colors in the rainbow (and this is how droplets of water act as prisms to split white light into its composite colors, producing a rainbow), white as a pigment color is produced by a total lack of pigment - no pigment color at all. Colored paints are made by taking a white base and adding concentrated pigments ('nothing' for color except a paint texture plus the color you want = paint texture in the color you want.) (On the other hand, "no" light color produces black - night! - whereas "all" pigments produce black - try mixing small amounts of many shades of crayon or paint together and you get a very dark, black color.)

So when you talk about a fish - that is presumably naturally pigment-colored some shade - turning "white" (in the dark or for whatever reason), you are talking about the color the fish normally has as physical little bits of colored pigment 'disappearing.' Well, if you know very much about science you know it is pretty hard to make something "disappear," but I studied the mechanism whereby fish do indeed turn color, and sometimes much paler color. So this is the best I can do in helping you understand your question and maybe the answer you are looking for.

The color pigment part of fish are located in their scales in little structures called "melanophores." The melanophore is part of the fishes' scale cells, just like the nucleus, mitochondria and whatever else fish scale cells have inside them. But these melanophores are only in the scales, which are on the outside of the fish and how we can see their color.

You might recognize part of this word melanophore as "melanin" - especially if you're concerned about getting too much sun = sunburn! Melanin is the pigment we have deep in our skin and which comes to the surface when our skin detects we are in too bright sunshine for too long. Our body's response is to bring melanin up from deeper levels to block some of that too-strong sunlight (which can damage our cells) - and gives white folks a tan! Some races, or some people, who have lived in the sun for generations or millenia have always-dark skin, people from India or Africa, for instance. So it's melanin pigment that colors our skin a darker brown shade.

Quite similar for fish - except fish either clump the pigment particles they have together inside the melanophore, called aggregation, or they let the pigment particles float free and loose within the melanophore, called dispersion. And when I say the fish "do" this, it's a pretty unconscious mechanism, they don't have any thinking control over this, it's a pretty much instinctive response. Fish species that can do this usually do it for one of 2 reasons: either they are frightened or they find themselves in much brighter or darker surroundings.

There are 2 chemicals that circulate in fish bodies that principally affect this color-changing mechanism: potassium and adrenaline. Potassium is in all animal cells, it's in the fluid that surrounds them, too, but for specific reasons parts of animals' brains can direct a build-up of potassium in certain parts through the nerves to that part of the body. In this instance, we're talking about more potassium being directed to the fishes scales when the fish is placed in a darker environment. It happens automatically: the part of the fish's brain that detects light levels says, "Less light, more potassium to the scales" - and the pigment in the melanophores aggregates - it clumps together and makes the fish scales look darker. And the reverse - more light, less potassium to the scales, a lighter-appearing fish to blend in with the surrounding lighter water. Ditto for when danger is sensed - the brain directs the release of adrenaline throughout the fish's body (which helps it swim and breathe faster) and the effect of adrenaline on the melanophores is that it causes the pigment in them to clump together. Adrenaline causes the fish to become darker, causing the fish to blend in better with the darker water, which is where it swims to when threatened.

Now the trick here, as I mentioned above, is nothing is really disappearing or appearing out of thin air, the pigment simply either aggregates or it disperses within the melanophores. However, the effect to animal eyes is that it appears darker when pigment is aggregated and appears lighter when dispersed. (You can try a similar experiment with a computer printer: make a large, filled-in object like a solid circle varying shades of grey with the color palette of your word processing or drawing program. As there is more pigment - printer ink - in the same amount of space, the object appears darker grey, and the reverse. Look for the little, tiny ink spots with a magnifying glass and count them - the more there are in the same amount of space the darker the object appears. This is not exactly the same as how a melanophore works, but without descaling a goldfish and a microscope and some laboratory solutions, this is a good, safe analogy.)

Now back to your specific question about a fish turning white in the dark. This would be completely the opposite mechanism from the way fish coloration normally works, and therefore pretty rare if at all. A fish that turned white in the dark would stick out like a sore thumb and could become much easier prey for predators! But as I say, there may be some strange species that do this and hopefully someone will let you know about these exceptions.

Another thing that happens in a lack of light sustained for generations is that whole species of animals can become 'albino' - they turn white and have no pigmentation anywhere at all. There are several kinds of fish that live in very dark caves or at the very bottom of the ocean (where no practical light reaches) that have become albino. You could search for "albino fish" on the internet and you would find lots of information about those species, but this is very different from what your inquiry.

I hope this helps you figure out what you're asking about!

Answer 2

No, fish do not change their color to white if kept in a dark room. Fish can experience stress and color change due to various factors like water quality, diet, and genetics, but darkness alone would not turn a fish white.