Abstract. Silver pompano (Trachinotus blochii) has received tremendous attention from the aquaculture sector, due to its favourable features, such as a high economic value, its good adaptive response and its potential to be cultured in various salinities. The aim of this study was to discover the effects of medium salinities on osmotic performance rate, blood cortisol, and growth performance (absolute growth weight and lenght, specific growth rate (SGR), feed conversion (FC), feed efficiency (FE), survival rate (SR)) of T. blochii under recirculating system. The histological alterations (kidney and gill) and water quality (temperature, pH, DO, NH3, NO2 and NO3) were also observed. The 56-day experiment was carried out in Balai Perikanan Budidaya Laut (BPBL) of Batam, Indonesia. A total of 300 fish specimens (11-13 cm in length, weighing 28-29 g) were raised in a 100 L tank containing 80 L of water at a density of 1 fish 4 L-1 (20 fish in total). They were fed with commercial pellet (46% protein) at 3% of fish biomass and 3 times a day. The experiment was conducted according to a completely randomized design with 5 levels of salinity: P1=25‰, P2=20‰, P3=15‰, P4=10‰ and P5=5‰, by performing triplicate measurements for each treatment. The treatment with 15 ‰ salinity showed the best effects, yielding an osmotic performance rate of 3 mOsm L-1 H2O, a blood cortisol level of 50,923 nmol L-1, an absolute growth weight and length of 17.73±1.25 g and 2.32±0.21 cm, respectively, an SGR of 0.87±0.05%, an FC of
1.24±0.00, an FE of 80.79±0.58 and an SR of 88.33±2.88%. Histologically, there were no anomalies in the structure of gill and kidney of the fish cultured in 5‰-25‰ salinities. Water quality was acceptable for growing T. blochii.
Key Words: gill, kidney, blood cortisol, histology, water quality.