Trenac, I couldn't find a disease that matched the one I have. Could be swim bladder disease; however the puffiness is un-equal on both sides. Also their seems to be a yellowish/greenish hue under the skin. (Is this normal for swim bladder disease?)
Ted, I wish I could help you more; but I'm not good with diesease. Hopefully someone else will come along that will be able to help. I always keep Melafix (antibacterial) & Pimafix (antifungal) around the house in case I get a unknown problem with my fish. You can dose each at the same time, it is all natural and will not harm fish/plants. I usually dose half dose of each at the sametime.
Swim bladder is possible, since they don't always look like the textbook examples, and loaches don't have scales which is a helpful diagnostic clue. How is he swimming? Usually with swimbladder, they have a hard time swimming normally.
Another possibility is internal parasites. That would be treatable with a deworming recipe that you can use with food.
The last possibility is an internal tumor, which you can't do much about.