The invention provides for a process that enables live-bearing fresh water fish to live and breed in a salt water environment such as an aquarium. The process starts with a live birth of fry in an aquarium where the salinity of the water matches the salinity of amniotic fluids. Once the fry stabilize, the salinity can be gradually increased to match the salinity of a standard salt water aquarium. The fry and their offspring mature, live, and breed in salt water with no future intervention.