How to breed ranchu
Ranchu breed readily. Raising the fry into ranchu that look like ranchu is the hard part, and it takes tub space, live food and a willingness to cull.
Breeding age and sexing
Ranchu mature at about one year, but breeders wait for two-year-old (nisai) fish at least, and prefer three-year-old females: bigger fish give more and better eggs. Sexing is hard outside of the season. In spring, males grow white breeding tubercles on the gill covers and the leading edge of the pectoral fins, and chase. Females fill out lopsidedly with eggs and have a slightly protruding vent.
Conditioning
Separate the sexes for two to four weeks and feed heavily: frozen bloodworm, brine shrimp, daphnia, and a high-protein pellet, three or four times a day. Keep the water very clean. In a cold climate, a winter rest at 50 to 60 °F followed by a slow rise to 68 to 74 °F is the natural trigger. Longer daylight helps.
Spawning
- Put one female with two males in a shallow tub (20 to 30 cm of water) with spawning mops, a bundle of yarn or fine plants for eggs to stick to.
- Do a large water change with slightly cooler water in the evening. Spawning usually happens at dawn the next day or the day after: males drive the female into the mops, she releases eggs, they fertilize.
- A big female releases several thousand eggs. Remove the adults as soon as they are done; they eat eggs.
Eggs and hatching
Fertile eggs are clear amber; infertile ones turn white and fuzzy within a day and should be picked out. Keep the water at 70 to 75 °F with gentle aeration and, if you like, a light dose of methylene blue against fungus. Hatching takes 3 to 5 days. The fry hang on the sides for another two days living on their yolk, then swim free.
Raising fry
Free-swimming fry need newly hatched brine shrimp three to five times a day, or infusoria and green water for the first days if brine shrimp is not possible. Change water daily in small amounts. Growth is rapid; at three weeks the tails are visible, and by six to eight weeks you can see which fish have the split, spread tail and which do not. See eggs and fry for the week-by-week detail.
Culling
This is the step that makes a ranchu breeder. Of several thousand fry, the ones with a single tail, a fused tail, a bent spine, a dorsal spike or a poor back curve are removed in a series of passes at 3 weeks, 6 weeks, 3 months and again in autumn. What remains, often under 5% of the spawn, is grown on as tosai. Without culling you have a tub of goldfish; with it you have ranchu. Give away or sell the culls as pets if you can; they are healthy fish.