Why do most rainbows have a "stress bar"

[FrozenFins]

I have seen multiple pictures of rainbowfish online, all of which have what I thought was a stress stripe when it was on mine. I wanted to know if this is a stress bar and if it is why are they so prone to stress? And if it isn't, why is it that my rainbowfish stripes will come and go, but will usually be visibile. Heres an example:

I have noticed on my rainbows that there colors fade when they display this stripe (which is what I thought a stress sign), and I saw from another forum member today the same thing! I have also kept threadfin rainbows and they didn't have any of that stripe. I am wondering if its just usually on "bigger" rainbow species. Maybe its just the Rainbow Fish genetics?

 

[Colu]

I have seen a couple of vids with Gary Lang talks  about rainbow fish  colouring up

Edited January 25, 2021 by Colu

[Hobbit]

I’m curious about this for honeys too. Neither of my parent fish have a stripe or ever display one, but all the babies are born with one. As they get older their stripes do seem to darken with stress and fade when they’re comfortable, but then some fish lose their stripe entirely and some don’t (at least not before I take them to the LFS). I know some female honeys retain their stripe into adulthood. So I think it’s a combination of stress signaling and color genetics.