Folks,
That isn't gas bubble disease. By definition there would be gas BUBBLES. Those are fluid filled vesicles (blisters). If they were filled with gas the fish would have to be named "Bob" 'cause he'd be floating. It would also be dead because supersaturation causing that many gas bubbles would cause cavitation in the heart and kill it immediately.
Now - what caused the blisters? I don't know for sure, but viral infections have been implicated in some cases, as well as the flagellate Spironucleous (related to Heaxamita).
JHemdal
p.s. - airstones do NOT cause gas supersaturation, they actually relieve the problem - like shaking up a can of pop releases the dissolved gases. Microbubbles are not the problem, it is gases actually dissolved in the water (that you cannot see) that cause this gas bubble disease. Common causes include leaks at the suction side of strong pumps and de-gassing caused by huge changes in water temperature.