The acquisition of Fifita, who attracted interest from a number of clubs, is a major coup for the Sharks, while Gibbs will add plenty of muscle and a wealth of experience to the Cronulla forwards from 2012 onwards.
Fifita has been one of the leaders of the Tigers pack in 2011, impressing many good judges with his robust style of play, while Gibbs, a member of the 2005 Premiership winning side, has played 143 games in the NRL and has three times represented City Origin.
Both players will see out the remainder of 2011 with the Tigers before joining the Sharks.
The signings come on the heels of the Sharks announcing that Kiwi Sam Tagataese has come on board for the remainder of this year as well as for the 2012 and 2013 seasons, while in further strengthening the ranks they have gained the services of accomplished playmaker Jeff Robson through until the end of the 2013 season.
Along with continuing to secure their young local talent, the Sharks will remain active in the player market in the coming weeks and months with more player signings expected.