The current study was carried out to detect the influence of various stocking densities on behavior and the biological performances of Nile tilapia (Oreochromis niloticus) fingerlings. Fingerlings (30±5g) were stocked in duplicate at four stocking densities; low density 15 (group1 as control), medium density 25 (group 2) and high density such as 35 (group 3) and 45 (group 4) fish/aquarium, in glass aquaria 30×40×100 cm for 10 weeks. The results showed that the surfacing behavior was higher in high stocking density reared groups than the low and medium density reared groups. Moreover, the aggressive behavior with all patterns was markedly higher in fish raised at high stocking density than the low and medium density raised fish. The crossing test showed that low density raised fish was more active than medium and high stocking density raised fish. Final body weight was markedly decreased with increased density, While, the fish reared at low stocking density showed a marked increase of daily weight gain (DWG). Finally, high-density culture is considered as chronic stress for Nile tilapia fingerlings due to increasing surfacing behavior and the appearance of all patterns of aggression.