This study describes an integrated culture system developed for Gracilaria chilensis Bird, McLachlan & Oliveira cultivation using salmon tank effluents, and tests the effects of algal stocking density, seawater replacement rates and CO 2 addition on biomass and agar production. Effluents produced by intensive tank cultivation of salmon were an effective source of seawater for the on-shore tank cultivation of Gracilaria in southern Chile, giving production values of 48·9 kg(wet)/m 2 per year; biomass yields were seasonal and agar yields were lower when fish effluent as opposed to pure seawater was used. During the seasons of high growth, the agar content of Gracilaria was lower in the tanks receiving fish effluents. However, the Gracilaria biomass production was sufficiently high to compensate for the lower agar content increasing agar production from 0·8 to 1·2 kg/m 2 by using fish effluents during an 11-month period. These results were obtained without an extra supply of nutrients or CO 2, with an algal stocking density of 3 kg/m 2, and with 10 seawater replacements per day.