Abstract. Red porgies, Pagrus pagrus L., of 70g were reared under self-feeding conditions in six successive compartments of the same raceway and their biological performance was studied in relation to their positioning in the raceway and the quantity of water needed to produce 1kg of fish. Daily gain of biomass was found to be similar in the first four compartments, and began decreasing in the fifth and sixth. The critical water quantity, below which biological performance was impaired, was 400 m3/kg of fish. No differences in mortality rate were observed between groups. The different biological performances were associated with the impaired feeding rates and conversion efficiency observed with groups A5 and A6. Results are compared with those of other species and are discussed in relation to the importance of this species for fish culture and the most appropriate technology for its production.