A fish pen (100) includes an elongate spar buoy (110) and an optional reserve buoyancy buoy (120) disposed over a top end of the spar buoy. One or more rim assemblies (130, 140) are attached to the spar buoy with tension members (150, 152, 154). An adjustable upper connection plate (114) on the spar buoy provides a means for tensioning the tension members. A docking station (190) and portal (185) provide easy access to the fish pen. A deployable panel system (180, 182) allows for crowding fish into a smaller portion of the pen. The panel system may be nonporous and include additional panels (184) such that a portion of the pen can be substantially isolated.
