Finite element analysis (FEA) is used to predict the dynamic performance of an offshore fish cage and submerged mooring grid system. The system has been deployed at an exposed demonstration site in 55 meters of water south of the Isles of Shoals, New Hampshire. Computer simulations were performed to investigate the dynamics of the cage motion and to calculate mooring line tensions. The results were used to establish the baseline design specifications and to evaluate the overall performance of the system.Both surface and submerged positions of the net pen are considered. It is shown that the extreme environmental loading conditions at the demonstration site produce 60% less mooring tension in the case of a submerged cage. According to the analysis, the case when one of four mooring legs becomes disabled will not produce the failure of the mooring system.The problem of adequate modeling of net is addressed. A simple technique is proposed to approximate the effect of netting on the overall dynamic response offish cage/mooring systems.