How long do ranchu live?
Ten to fifteen years is normal with good water. Most ranchu that die young die in the first few months, and almost always from the same cause.
The realistic number
A ranchu kept in clean, stable water lives 10 to 15 years. Well-documented fish have passed 20. The fancy body shape makes ranchu a little less hardy than a common goldfish, but not much; the difference in lifespan between a ranchu that dies at two and one that dies at twelve is almost always the keeper, not the fish.
What shortens a ranchu's life
- Ammonia in an uncycled tank. The number one killer of new goldfish. See why bowls fail.
- Chronic high nitrate from skipped water changes. It does not kill quickly; it wears the fish down over a year or two.
- Overfeeding and floating food, which leads to repeated swim-bladder episodes and gut infections.
- Temperature swings and cold winters in unheated rooms below 60 °F.
- Fast tankmates that outcompete the ranchu for food until it slowly starves.
- Extreme breeding. Very round, very short-bodied fish from some lines have more internal problems and shorter lives.
Age and appearance
A first-year fish (tosai) is 2 to 4 inches with little head growth. In the second year (nisai) the wen fills in and the body deepens. From the third year (oya) the fish is adult, 5 to 8 inches, and its shape is fixed. Growth slows after that, but a healthy fish keeps adding a little wen and body mass for years. The life stages page shows each stage.
Old ranchu lose some color intensity, the wen can become uneven, and they spend more time resting on the bottom. None of that is illness. Keep the water clean and the food soft, and an old ranchu is an easy fish to keep.