Effects of rearing density on leukocytes and plasma cortisol level of Siberian sturgeons (Acipenser baerii)

    This study was carried out to evaluate the effects of rearing density on total and differential leukocyte count and serum cortisol level in Siberian sturgeons (Acipenser baerii). Three years old Siberian sturgeons (460±90g) were reared at five densities (6, 9, 12, 15 and 18 fish per one third of 500-liter tank) for an 8 weeks period. To examine the total and differential leukocytes level changes, blood sample of one third tanks population were analyzed at the first and end of study with taking 3 blood smears of each sample. In high stocking densities (15 and 18 fishes) a significant decrease in total leukocyte count took place caused by a considerable drop in lymphocyte count but percentage of neutrophils increased significantly (P<0.05). No significant difference was found in monocyte and eosinophil percentage among the experimental treatments. There were no statistically significant differences in serum cortisol concentrations in different treatments (P>0.05). In overall, the results showed that: 1) chronic stress caused due to crowding condition reduced the immune potential of Siberian sturgeons. 2) Changes in blood cellular composition were better stress indicator than plasma cortisol levels in Siberian sturgeon.