Symptoms may involve:
- Inability to submerge fully
- Tilting upwards uncontrollably, fighting to reach the bottom of the tank
- Rolling sideways while trying to swim
- Bobbing on the surface with back bent into an s-shape
- Noticable bloating with swimming difficulties.
Basically, swim bladder disease often makes it seem like the fish's belly is full of air, which prevents it from swimming properly, submerging fully, staying upright, etc. If your fish had it, you'd probably be able to tell as they'd be quite off - though it can develop over time as the fish matures or due to injury. It is thought that a diet of all freeze-dried foods contributes as well, as it expands in the stomach, pressuring the swim bladder, and over time causing damage.