This study examined the effects of implanted cortisol (to imitate chronic stress) on the hematological responses and cortisol values of female great sturgeon, Huso huso, after an endoscopic operation. At the beginning of experiment, all the fish were examined using an endoscope to evaluate gonad development. Then, in order to mimic chronic stress following surgery, capsules of cocoa?? butter containing cortisol were intraperitoneally implanted to 3-year-old female fish in reproductive II stage (mean body weight 6759 ± 53.23 g). The implant doses were 0 (C0; as control), 5 (C5) and 50 mg cortisol /kg BW and there were five fish per treatment group. Blood samples were taken every week during the 28 days of the experiment to evaluate hematological responses and blood cortisol concentration. There were no significant changes in serum cortisol in C50 group during the experimental period, but an upward and significant trend in serum cortisol was observed in C5 group. Also, cortisol levels in C5 group were significantly higher than those of the control and C50 groups from second week after endoscopic surgery and implantation onwards. White blood cells increased after endoscopic procedure, but the response was lower in control fish than those receiving cortisol. Hemoglobin and hematocrit did not change with treatment or time. Significant differences were observed in the percentage of lymphocyte and neutrophil cells in the second and fourth weeks after implantation, so that lymphopenia and neutrophilia were observed following cortisol implantation. The present study revealed that exposing fish to chronic stressors after an endoscopic operation decreased the immune response and had an immunosuppressive effect. Also, these results suggest that great sturgeon exhibit a low response to slow release of cortisol compared to teleostean fishes.