Most common in fancy goldfish + bettas + mollies. Trapped gas affects swim bladder buoyancy. Fix: fast 2-3 days, then feed deshelled cooked peas.
Bacteria infect swim bladder. Treatment: Kanaplex in QT 7-10 days.
Some breeds (telescope eye, oranda, ranchu) have hereditary swim bladder issues. Often improves with shallow tank + low flow.
Sudden temp change disrupts swim bladder gas regulation. Fix: stabilize temperature.
Ammonia spike causes neurological symptoms. Test + water change.
Test water first - many "behavior" issues are actually water-quality problems. Use the water parameter checker to score your test results, the disease symptom matcher if you observe physical signs, or the general diagnoser to narrow further. Browse the full disease database if illness is suspected.
Browse all behavior troubleshooting articles.