That issue is super common in this species. They are collected deep, and because the divers work fast, they are decompressed with a needle as opposed to bringing them up slowly over a day or so. Very often, the swim bladder refills, and they float at the surface in aquariums. Shipping them by air (in lower pressure conditions) causes the issue to become worse. There isn't any treatment for this since there isn't any disease organism involved. I had made a pressure tank years ago that would resolve the problem, but when I bled the pressure off, it would return. Using a needle to draw off the extra gas also fails. They do sometimes recover on their own in time. If it is in a quarantine tank, you might be able to reduce the symptoms by lowering the salinity, which in turn would lower the buoyancy of the fish - but only by about 15% if you went from 1.025 to 1.020
Jay