Few sights alarm a fishkeeper more than a goldfish whose scales stick out like an open pine cone. That appearance is the classic sign of dropsy — and an important clarification first: dropsy is not a disease itself but a symptom of fluid building up inside the body, usually because the kidneys are failing. It affects bettas, goldfish, and most other aquarium species, and it is genuinely serious: by the time the belly swells, the fish is already in trouble.
Symptoms of Dropsy
- Swollen abdomen and scales that protrude outward in a “pine cone” pattern, most obvious when viewed from above
- Bulging eyes
- Clamped fins and loss of colour in the gills
- Lethargy, hiding, or resting on the substrate
- Loss of appetite and pale, stringy faeces
- A curved spine or swelling near the anus in advanced cases
The underlying driver is usually a bacterial infection with Aeromonas, a microbe that is always present in the tank. It only becomes a problem when a fish’s immune system is weakened — most often by poor water quality, ammonia or nitrite spikes, unstable temperatures, or a poor diet. That is why the real cause of dropsy is rarely the bacteria; it is whatever stressed the fish in the first place.
When to Act
Act the same day you notice early swelling, raised scales, or a fish that stops eating. Dropsy advances fast, and once scales are fully raised across the whole body, treatment success drops sharply. If the fish is also gasping at the surface, seriously bloated, and has stopped eating for several days, the internal damage may already be irreversible — an honest conversation about humane euthanasia with clove oil is sometimes the kindest option at that stage.
Common Vet-Directed and Hobbyist Treatments
There is no single cure, but a multi-step approach gives the best chance:
- Quarantine immediately. Move the fish to a bare hospital tank with a gentle sponge filter and a heater, around 26–27°C for most tropical fish. This protects tank mates and lets you medicate without harming the main tank’s biological filter.
- Epsom salt (magnesium sulphate). Dissolve about one tablespoon per 20 litres. Unlike ordinary aquarium salt, Epsom salt draws excess fluid out of the tissues through osmosis and can visibly reduce swelling within a day or two.
- Antibiotics for bacterial causes. Kanamycin and metronidazole are the most commonly used medications for the gram-negative infections behind dropsy; follow the label course completely.
- Fix the water. Test the main tank for ammonia and nitrite at once and do daily partial water changes until both read zero.
Home Care During Recovery
Keep the hospital tank dimly lit and calm, feed small amounts of high-quality food (soaked antibiotic-medicated food if the fish is still eating), and perform small daily water changes with pre-mixed, temperature-matched water so parameters stay stable. Watch the fish from directly above each day — that is the best angle for judging whether the swelling is improving.
Prevention
Prevention beats treatment every time. Quarantine all new fish for two weeks before adding them, avoid overstocking, keep a consistent water-change schedule, feed a varied diet rather than one food only, and maintain stable temperatures. Clean filter media gently in used tank water instead of tap water to preserve the beneficial bacteria that keep ammonia at zero. A low-stress fish in clean, stable water rarely develops the immune failure that lets Aeromonas take hold.
This article is for educational content only and is not a substitute for professional veterinary advice. For a specific diagnosis and treatment plan, consult an aquatic veterinarian or experienced fish health professional.