One of my FH fry remains at the surface constantly, at times with the tip of his dorsal protruding above the water. His abdomen seems a bit swollen. Scales are not protruding, so it is not dropsy. I netted him yesterday to check him and the swollen area seems not to be solid. Possibly air- an air bladder ailment? He had a sunken in belly when I first got him, but he started eating and rounded that out a bit. A day or two later, he's got a swollen abdomen. Any advice?