Growth in fish is determined by many factors both physiological and environmental. Factors such as parentage, sex, diet, water conditions, age, Maturity, Temp etc. All of this can impact total growth for a given year by an individual fish. Fish in captivity are on a very different water change and diet schedule that those in the wild. One they get 100% waterchanges daily and two they forage at will. They also have an open ability to select optimal habitat.
In captivity they do not receive the same conditions. We generally feed our fish in a manner best described as "stuff and starve". They receive a set amount of food and that's it. This does impact growth. Small bodies of water are also more likely to concentrate wastes much quicker. I do not care how much filtration you have or how many waterchanges you do a week, you can not replicate natural water conditions in captivity. Co-habitation with other fish in a small system also impacts the fishes growth through psychological stress as well as competition for food and living space.
Osseus are capable of reaching 19 inches in one year however it is much more common for them to reach 12 to 14 inches during the growing season and then slow until the next years growing season at which time they quickly jump to 19 to 20 inches. Third year growing season they again quickly bounce up to 24 to 30 inches.
At this point sex of the fish will determine growth to a large degree. Female will grow quicker, thicker and larger throughout each season up to year 6. Males pretty much slow down or stop growing much after the 3rd year. At this point males are reproductively active.
