I have never had Ranchu’s myself so don’t know that much about them. However, I do know that if they have a small wren as a baby, they will probably have a small one as an adult. A lots depends on genetics and nutrition.
Proper temps, nutrition and clean water make all the difference. The “bump” or cap should be evident at month four. And while I think the Oranda is cutely deformed, the Ranchu just takes it too far for me.
If you have ranchu fry, get a good supplier of bloodworms. They love em.
My ranchu is about 4 months old, I just recently purchased her from a breeder. She doesn’t have a wen (the cute bumpy things) yet. I can tell that she has a little layer of wen tissue on her head and face, though, so I suspect it will grow.
My oranda has just recently gotten a noticeable one, even though I’ve had him for over a year.
A lot of it has to do with both genetics and foods. Higher protein equals faster wen growth, from what I understand. But it will gradually grow with age.