Abstract: An offshore aquaculture system for use with an oil or gas well production platform or like offshore structure is provided. The platform is preferably supported in four (4) directions by radially extending guy wires that attach to the upper end of the platform at one end of each wire and to the seabed at anchor piles at the other end of each wire. Anchor piles are driven into the seabed a substantial distance to provide anchorage for the undersea end of each guy wire. Fish pens are mounted to slide and travel on the diagonal guy wires and can be elevated or lowered relative to the seabed using ballast tanks attached to the fish pens and an endless winch line. The winch line is operated with a powered winch mounted on the platform deck. An opposed idler sheave is mounted at the seabed engaging the endless cable.