Fingerling beluga sturgeon, Huso huso (Linnaeus, 1758) growth, hematological, biochemical parameters and opercular respiratory rate under hypoxia challenge with levels of dietary folic acid

Folic acid (FA) is an essential water-soluble vitamin, that is unstable in environmental condition and does not regard in vitamin premixes in spite of its importance. In this study 270 beluga sturgeon fingerlings with weight of 5-8 g were fed by various levels of FA: 0.6 (Control/treatment 1), 2.68 (treatment 2), 3.72 (treatment 3), 4.84 (treatment 4) mg kg-1 feed with three replications for 56 days. Effect of treatment groups on growth, hematological, biochemical parameters before and after stress and opercular respiratory rate (ORR) during stress was investigated in fish fingerlings. The results showed the treatments has significant differences on FCR, SGR, feed efficiency and weight gain (p<0.05). the treatments has significant differences with the control group on red blood cells (RBC) count, hemoglobin (Hb) and Hct (P<0.05). Before stress, cortisol and glucose levels among treatment groups had no significant differences, but after stress they had. Minimum and maximum responses in cortisol levels were observed in treatment two (427.92 +/- 6.05 ng mL-1) and control groups (830.32 +/- 5.97 ng mL-1), respectively. Minimum glucose levels (43.75 +/- 1.49 ng mL-1) in control group and the maximum in treatment two (58.25 +/- 1.49 ng mL-1) were observed.There were significant differences for ORR in 0-5, 5-10, 10-20, 30-40 minutes during oxygen challenge among treatment groups (p<0.05). But this indicator in 20-30 minutes was not affected by treatments. The results of this study, showed that the fish with FA 3.72 mg kg-1 diet have more resistance against environmental oxygen challenge, therefor can be stated FA may lessen the negative effects of stress in beluga sturgeon fingerling.