they get 16 inches when full grown. ive hade a few box fish and all have perished with no other complications but im not very nice as soon as they start to get real weak and show signs of not pulling through i remove them and freeze them. as soon as they stop swimming and breath is shallow ill remove them. ich is worst thing that can happen to a box they usually dont pull through. i got mine from ER, they have sold a few others that where eating pretty well before leaving, so louis is doing something right.