Hamidreza Nooryazdan

Due to its rapid growth, easy reproduction, wide range of salinity tolerance and ability to adapt to formulated feed, Asian sea bass is one of the best cultured species for intensive aquaculture in recirculated system. In this study, Asian sea bass fry with approximate weight of (2.34 ±0.32 g) were randomly distributed in 12 ten-ton concrete pools of a 9,000-liter nursery with a commercial closed-loop system. Four treatments (6, 7, 8, 10 fish per liter) and 3 replicates were selected. Water quality parameters were studied daily and growth factors were recorded ate the end of the experiment. Results showed a direct relation significant difference between ammonia and density of all treatments with the highest result in 10 fish/l treatment. Daily and absolute weight gain was influenced by treatments, and the highest growth rate was observed at 8 fish/l treatment (p?0.05). With a significant different (p ?0.05), the highest and the lowest specific growth rate were seen in 8 and 6 fish/l, respectively. There was no significant difference (p ?0.05) between daily and absolute weight gain of 6 and 7 fish/l and 7 and 10 fish/l density. Survival rate showed an inverse relationship with stocking density. Survival decreased as stocking density increased. The highest survival rate was at the lowest density (6 fish/l). Also, the lowest survival rate was observed in 10 fishes/liter density (p ?0.05). Increasing fish density results in increasing aggressive and competitive behavior, cannibalisms, abnormal swimming and low survival rate.