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