Due to limited nearshore areas and great impact to local ecosystems, the aquaculture industry is moving the fish farms from nearshore to more exposed sea regions where waves and current are stronger. Like other offshore installations operating at sea, fish cages are also exposed to the risk of collisions from attendant or visiting vessels. This paper evaluates the structural strength of a fish farm concept subjected to supply vessel collisions by the use of nonlinear finite element simulations. The fish cage is made of ring-stiffened columns and supporting braces. A 7500-ton supply vessel is used as the striking vessel. Several collision scenarios with both coupled and decoupled methods are simulated on representative impact locations. The results are discussed with respect to the impact resistance, energy and structural damage.