Polyculture of European seabass and Nile tilapia in the recirculating aquaculture system with brackish water: Effects on the growth performance, feed utilization, and health status

Non-traditional aquaculture practices are crucially needed to overcome the climate change consequences, especially in countries suffering from water shortages. Polyculture strategy depends on the diversification and compilation between different aquatic animal species to fasten farmed species' growth and improve available resources' utilization. In this study, European seabass and Nile tilapia were poly-cultured in brackish water (salinity 12) in a recirculating aquaculture system (RAS). For this reason, fish were distributed into five groups with triplicates in each. The first group (G1) of aquaria (120 L) was stocked with 40 specimens of European seabass, the second group (G2) was stocked with 30 specimens of European seabass + 10 specimens of Nile tilapia, the third group (G3) was stocked with 20 specimens of European seabass + 20 specimens of Nile tilapia, the fourth group (G4) stocked with 10 specimens of European seabass + 30 specimens of Nile tilapia, and the fifth group (G5) stocked with 40 specimens of Nile tilapia. The dissolved oxygen (DO), total ammonia nitrogen (TAN), and NH₃–N showed higher levels in G2, G3, G4, and G5 than in G1 (P < 0.05). Except for G5, European seabass showed higher growth performance indices (FW, WG, and SGR) and lower FCR in G4 than in G1, G2, and G3 (P < 0.05). On the other hand, Nile tilapia growing in G2 resulted in higher FW, WG, and SGR and lower FCR than in G3, G4, and G5 (P < 0.05). The total biomass of poly-cultured European seabass and Nile tilapia is higher in G3 than in G1 and G5 (P < 0.05). All groups had no significant differences in the somatic indices (P˃0.05). In European seabass, the crude protein and total lipids were significantly increased in fish compared to the initial carcass composition (P < 0.05). Besides, in Nile tilapia, the total lipids were significantly increased in fish compared to the initial carcass composition (P < 0.05). Furthermore, no significant differences were seen between all groups (P＞0.05) on the blood total protein, albumin, globulin, ALT, and AST. In conclusion, the polyculture strategy is appropriate for farming European seabass and Nile tilapia in RAS with brackish water without compromising growth performance, health status, and survivability.