I see, so I must have a certain line in my pond that when they breed, it is producing the bigger bulkier koi that those 3 orange ones? They are so healthy and bulky looking all the time. Maybe I should keep them and let some of the smaller ones that don't grow go to keep the robust line going? lol. Most of my customers have ponds smaller than mine.( Both over 4000). A lot of the time the size of the fish can be determined by how much they are fed and the type of food. I use a color growth food and feed several times a day. That can give you a 24" koi in 2 years! Genetics also play a roll. I have some koi 10 years old at 18".