This study was undertaken to evaluate the effects of temperature fluctuations on growth rates, hematological indices and body composition of Acipenser baerii juvenile during a 120 day trial. A total of 120 juveniles (initial body weight: 132 ± 4.2 g) were stocked in triplicate groups (10 individual per replicate) in 12 fiberglass tanks (500 L capacity). Four temperature regimes were applied: The first group was maintained as control at constant 22 ± 0.6°C (mean temperature around which the temperature of the other test trials fluctuated). The second group was exposed to temperature fluctuations between 19 and 25°C over a 24 h cycle, starting with the upward part of the cycle during daytime (feeding period). The third group started the exposure of the 24 h temperature cycle at the higher value (at 25°C; declining over the daytime) while the fourth group was exposed to two complete daily cycles of the same temperature fluctuations (between 19 and 25°C). Biometry of fish (total length and weight) was determined monthly. Blood samples were also collected every month and body composition was determined at the end of the experiment. After 17 weeks final weights were significantly affected by the daily temperature fluctuations (P < 0.05). The highest final weight and SGR was recorded in regime 2 followed by the control. The Highest body protein and lowest body lipid were recorded in fish exposed to the fourth temperature regime (two full temperature cycles in 24 h). Fish reared under this temperature regime also showed significantly lower blood plasma glucose levels than the other treatments (P < 0.05). Hemoglobin and hematocrit content in blood samples were not affected by any of the tested daily temperature fluctuations (P > 0.05). The leukocyte count increased slightly in regimes 2 and 4 compared to regime 1 (control) but differences were not significant (P > 0.05). These results tentatively suggest that some temperature fluctuations on a daily cycle can improve growth rates and enhance the immune system in Acipencer baerii. However, the optimum frequency and amplitude for temperature undulations remain to be investigated in more detail.