well i own a couple and one has grown about 3 inches in the 2.5 months ive had him, and is close to is about 4 inches now, he'll probably start to slow down a little, but he'll surpass 6 inches. i think it depends on their parents, and overall health of the fish, people that dont own them have alot of generalizations about them, so look into it and go to bluejax.co.uk for the best advice