I've never really frozen whole fish for filleting at a later date although (occasionally) I have stored them on well drained ice for up to two days before filleting. But, as for fillets... I've always frozen mine in salt water in freezer bags... but I still make it a point to label them by date and rotate the cooking dates... cooking older ones first much like the grocery store rotates stock moving the older merchandise to the front to keep everything fresh and moving as it is sold or in the case of fillets... used. About six months is the preferred amount of time that I personally like to keep filleted fish frozen although I have and will probably go longer than that from time to time.
"Just Like Iron Sharpens Iron... So it is that One Man Sharpens Another Man." Proverbs 27:17