just to answer your question, they only glow under a black light.
This effect is accomplished via gene splicing - originally with Zebra fish.
Since humans have tinkered so much with Betta genetics, I'm not necessarily opposed to glowing Betta, tho I wouldn't buy one because blacklights can't grow plants.
If we can manufacture a pug from a wolf (try cramming 42 teeth into that flat face) then who knows maybe glowing dogs are next, LoL.
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