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The influence of colored light and tank color was investigated on growth performance (body weight, growth rate, carcass composition, etc.) and physiological status (blood and plasma parameters) of beluga (Huso huso) juveniles. The study was conducted using 64 specimens for colored light treatments with initial weight 98.83 ± 1.42 (mean ± SE) g which were reared under white, red, green and blue light and using 80 specimens for tank color treatments with initial weight 98.50 ± 1.24 (mean ± SE) g which were reared in white, red, green, black and blue tanks, all for 12 weeks. Red light had a significantly negative impact on beluga growth performance (in contrast with blue light) accompanied with reduced liver total lipids and plasma albumin and elevated plasma cortisol, glucose, cholesterol and triglyceride (in contrast with the other treatments). No significant effects of tank color were detected on growth performance. Nevertheless, most of growth parameters suggested a positive impact of black tank. Although plasma glucose levels in white tank were significantly higher than the other tank colors, no significant effects of tank color were detected for the other physiological parameters. Therefore, based on the obtained results, blue light by establishing comfort in beluga juveniles spelled increased growth performance and had positive significant effect on physiological conditions. Moreover, taking into consideration the consistency of all growth parameters among beluga juveniles reared in black tanks, it is suggested that considerable results in regard to this treatment may be achieved if the rearing period prolongs.

The e¡ects of constant light (24L:00D), no light (00L:24D) and two light^dark periods (18L:06D; 12L:12D) on the growth, stress and haematological variables were assessed in juvenile great sturgeon, Huso huso. During the 8-week experimental period, juveniles (22.5 AE 0.6 g) were kept under a 150 lx light intensity in ¢breglass tanks (0.8 m 2 , 500 L). Di¡erences in growth were insigni¢cant during the experiment, but lactate levels were higher in the 00L:24D and 24L:00D photoperiods compared with 12L:12D and 18L:06D photoperiods. Cortisol levels did not show di¡erences among the various photoperiods. At the end of the experimental period, ¢sh reared under a 12L:12D photoperiod had higher haemoglobin values and erythrocyte numbers than in the other photoperiods, while no di¡erences were found between groups with regard to haematocrit values or leucocyte numbers. The highest survival rate (89%) was observed in the 12L:12D period in which the levels of lactate and cortisol as stress indicators were minimal. The results indicate that various photoperiods cause di¡erent stress levels in juvenile great sturgeon and have no signi¢cant e¡ects on growth, at least in short time periods.

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