It depends on the cause whether your other fish will be affected or not. The difficult thing with dropsy is its a symptom, not a disease itself. It indicates systemic organ failure, namely the kidneys (which can no longer correctly process fluid). The causes are numerous. Anything from parasites and protozoa to bacterial infections to poor water quality (or any combination there of) are just a few factors. Trying determine a singular causative factor is what makes dropsy difficult (if not impossible) to treat. Even when successfully treated, most fish will still succumb weeks or months later due to irreparable organ damage.
Can you provide some info? Type of salt/%? Type antibiotics/dosing schedule? Type of fish? Tank size? Parameters? Any other info that may help (past disease history, present symptoms, etc)?
