I can attempt to ID those other fish if you would like! Also Cory cats generally should be kept in tanks of the size 20 gallons and like to be In groups of their own kind. What are you feeding him? I feed mine a nice high quality pellet and flake like Omega One shrimp pellets, New Life Spectrum freshwater sinking pellets and an Omega One freshwater flake. Your food may be what's causing it and if it's a lower quality food like Tetra or Wardly or something that may be the problem. If that's the case get him on some nice high quality foods like Omega One, New Life Spectrum and Hikari! You could cut down on his feedings (and switch foods if necessary) and if he's still bloated try feeding him some de shelled peas.