Dropsy in betta fish is typically caused by overfeeding, feeding inappropriate foods, and poor tank conditions. Dropsy is not a disease in itself, but a symptom of a bacterial infection and the resulting kidney problems. Because the kidneys are not operating correctly, the fish will retain water, and we see the bloating and pinecone-like scales we associate with dropsy.
While any fish can potentially become infected, stress caused by the aforementioned overfeeding and poor water conditions can make a fish more susceptible. Strong, healthy fish have immune systems that can better deal with infections, where fish weakened by poor diets and bad water will fall ill.
Therefore, the most important things in avoiding dropsy for your betta fish are to avoid overfeeding and to keep the water clean. These two steps, if done properly, can help you avoid many diseases and conditions that lead to a premature death for aquarium fish. This means following a proper feeding schedule – perhaps including a fasting day week – and performing regular tank maintenance such as changing the water and vacuuming the gravel.
If your betta fish does show signs of dropsy, the outlook is not good. However, there are some actions you can take if symptoms are recent and relatively mild, such as performing a water change and administering an antibiotic. If your betta lives with other fish you may wish to quarantine him, as the same issue that led to his illness may make them sick as well.
Finally, if you do lose a fish to dropsy and are convinced you did nothing wrong, remember that, just like people, some fish are naturally weaker and more prone to getting sick. It may have been simple bad luck, and no fault of your own.