We have a large tank with about eight red parrot fish, the largest one has what looks like a balloon under its belly and I'm just wondering what it is? I have done some research and they have been showing characteristics of pre-breeding and I have seen a picture of a females breeding tube witch two of our fish have these, but it looks nothing like the bubble under its belly. Does this have anything to do with breeding or should I be concerned?
She may be gravid with eggs, but it could also be something more serious. Are you sure all the water parameters are correct, and do you change about 25 percent of the aquarium water every week? Any sort of water quality issues can make fish vulnerable to diseases and parasites.
After correcting any water quality issues, you may need to medicate the fish. Here's a compilation of fish diseases and cures:
http://www.myaquariumclub.com/how-to-recognize-and- treat-disease-in-fish-what-is-wrong-with-my-fish- 477.html