Pikeperch (Sander lucioperca) is one of the most appreciated fish species found in many European countries, in natural waters and in fish farms as well. This species started to be reared into recirculating aquaculture systems (RAS) in the last decade, but the farming technology has to be improved continuously in order to increase the fish production and to reduce the production costs. The aim of this paper was to reveal the preliminary data of a study regarding two polyculture variants of the pikeperch, with European catfish and with sterlet, in order to emphasize the best candidate species for polyculture in RAS. The pikeperch and sterlet fingerlings used in our study have been obtained in RAS, in the spring of the year 2017, from broodfish exclusively reared in RAS. When the study starts, the fish were 6 months and 5 months old, for pikeperch and sterlet, respectively. The European catfish fingerlings have been obtained through artificial method using broodfish from ponds, and reared in RAS until the age of 4 months, when our study starts. The RAS used for the fish rearing had four tanks, with 1 cubic meter of water each. Two variants of polyculture have been tested in 2 replicates: pikeperch with sterlet, and pikeperch with European catfish. The fish biomass of the additional species represented about 21% from the pikeperch biomass in each variant. The fish were fed with dry feed SUPREME-10, size 3mm (Coppens International, Nederland), the amount being calculated as 2.5% from pikeperch biomass in the first 2 weeks, and then reduced at 2% from pikeperch biomass. The main body traits (total length, standard length, maximum high and body weight) were measured at the beginning of the study, and afterwards at every 14 days covering the period of this preliminary study. Based on the data obtained after the measurements, the main bio-productive indices like Weight Gain (WG), Specific Growth Rate (SGR), Daily Growth Rate (DGR) and Feed Conversion Ratio (FCR), have been calculated. The results revealed that both species used in our study as secondary species in polyculture with pikeperch, have been suitable and led to a better valorization of the feed into RAS, but the polyculture of the pikeperch with European catfish seems to be more advantageous. Anyway, our study must go on for a better understanding of all aspects linked to these polyculture formulae used for pikeperch farming in RAS. [ABSTRACT FROM AUTHOR]