Why is my ranchu floating upside down?
It looks like an emergency. Most of the time it is a digestion problem in a fish shaped like a ball, and it clears in a few days if you change how you feed.
What is actually happening
A ranchu's body is short and round. The gut, the swim bladder and the organs are packed into a space that would be twice as long in a common goldfish. When the gut swells, from air gulped at the surface or from a backlog of food, it presses on the swim bladder and the fish loses trim. It floats at the top, tips to one side, or turns over completely.
This is often called swim bladder disease, but in ranchu it is rarely a disease. It is mechanics. The fish is usually alert, its eyes are clear, and it still wants food. Those are the signs you are dealing with digestion and not an infection.
The two-day fix
- Stop feeding for 48 hours. The fish will not starve. Let the gut empty.
- Test the water. Ammonia and nitrite must read zero, nitrate under 20 ppm. High nitrate on its own makes goldfish float. If numbers are off, do a 40% water change with temperature-matched, dechlorinated water.
- Check the temperature. Below about 65 °F (18 °C) digestion slows and floating gets worse. Bring the tank up slowly, no more than 2 °F a day, into the low 70s.
- On day three, feed one blanched, skinned pea. Peas are fibrous and pass through. Then return to small feeds of sinking food.
How to stop it coming back
- Switch to sinking pellets or gel food. Floating flakes make ranchu gulp air with every bite. This single change fixes most repeat floaters.
- Soak dry pellets for a minute before feeding so they do not expand inside the fish.
- Feed small amounts, two or three times a day, instead of one large meal. What the fish clears in about two minutes is enough.
- Add fiber: peas, blanched spinach or duckweed once or twice a week.
- Keep the water shallow and warm enough. Breeders raise ranchu in tubs around 30 cm deep for a reason. See the care guide for the numbers.
When it is something else
If the fish is also sitting on the bottom, has clamped fins, red streaks in the tail, a swollen belly with raised scales, or has stopped eating, you are past a gut problem. Those signs point to a bacterial infection, dropsy or an internal problem. Improve the water first, then treat with a broad-spectrum medication and salt at 0.1 to 0.3%, and keep the fish in a shallow tub so it does not have to fight to reach the surface.
A fish that has floated on and off for months and always recovers may simply have a body shape that is prone to it. Some ranchu are bred so round that they will never be fully stable. Shallow water, sinking food and patience is the whole treatment.