A few days ago I noticed that one of my neons was looking a little pale. It now looks bloated and bug eyed also. It is also continually opening and closing it's mouth rapidly. It hasn't eaten in a couple of days and has just been hanging out in one section of the tank hiding behind some plants.

If anyone has any suggestions as to what is wrong and how to treat it, I would greatly appreciate it. I tried looking up fish diseases online but I didn't find anything that seemed to fit. My other fish seem ok so I hope it's not contagious. I have 6 other tetras, a swordtail & 2 oto cats in a 20 gallon tank.

Thanks!