That depends on SOOOO many variables. Such as type of fish and water
conditions, size of tank, food (amount and quality), to name a few. A photo
of a 15" oranda was being passed around a while ago, and someone said it is
now 18"!
The quality of the feed is important. One of my telescopes lost an eye a
while back, and I swear he grew 1/2 an inch in the 3 weeks he was on the
medicated food, which is better quality than the food he regularly gets.
I'm sure others can help you better than this, but this is my understanding.
Tammy