I read somewhere that all fish have light colored bellies as some kind of protection from predators coming from beneath them. If they had dark bellies they would be too easy to spot from below.
As long as she is acting healthy otherwise she should be fine.
Hi you can not be sure but it sounds like your betta may have White Slime Disorder
Stringy, white mucus on the body, highly contagious.
Treat the fish with an antifungal, treat fish he has had contact with, and scrub, scrub, scrub the tank or bowl with bleach. If he's been in a community aquarium, I'm sorry, but you're going to have to dismantle the entire thing, sterilize it, and recycle it before putting the fish back in. Yes, it is THAT bad.
However seek others opinions a picture of the ill fish might help diagnosis.
Dont be alarmed I may be wrong but hope this post helps you towards finding the problem
Umm... she didn't say it was slime, just that her belly was white. ALL fish have light colored bellies. I don't think she needs to do anything quite that drastic!
Genie: can you elaborate on this? Is it just white coloring or slime? Was it always white or has the color changed since you got her?
Sometimes stress can pale out their color for awhile. My red female Whisper would turn from deep red to light pink when she was stressed.
Oh Good! Jewel is my only girl who isn't very light already, so I thought it looked different. cobalt is the only other one i have that is dark and he doesn't have a light belly. I am just glad she is normal.