Why does Monterey Bay Aquarium's Seafood Watch program identify RAS fish as a "best choice" for consumers? Recirculated aquaculture systems are biosecure, preventing the escape of nonnative fish. Recirculated aquaculture systems filter solid waste from which a biofuel can be harvested. Raising fish indoors in RAS operations lowers their feed conversion ratio. Raising fish indoors in RAS operations may be taking some pressure off wild stocks