The first year they grow fast, I had some go from a body the size of a nickle to over six inches in about 9-10 months, but then form 6"-around 9" took about the same time, they only got about an inch bigger in the following year. The largest I ever had I got at 12" and it took just over 4 years to hit the 14" mark when it died during a power outage. Outside of Steinhardt Public Aquarium it was the largest natterreri I have ever seen.