[oO.Fish.Oo]

I have had this one guppy for almost a whole year now.. she is all yellow with a slight tint of red on her tail. I had gotten several over guppies and over the course of the fall they have all died off for some reason and now I only have her left - well and the many babies the other female left behind. Anyway I had the babies moved into a fish bowl with no filter while Pebbles (the yellow female) and the 5 gallon with filter to herself. She's eating fine and swimming around normally but the other day I realized that along her spine near her tail the yellow colour seems almost a pastel colour... I don't think it was like that before. I'm scared that its some kind of bacteria or something. I will try and get a picture but I've been searching around the internet for help and I thought I could ask here. Thank you for all your help in advance.