Immune response of great sturgeon (Huso huso) subjected to long-term exposure to sublethal concentration of the organophosphate, diazinon

Lysozyme activity, chemiluminuscence (CL) response and immunocompetent cells population size were assessed in great sturgeon (Huso huso) weighing about 425 g following long-term exposure of fish to sublethal concentration of diazinon at 1.5 mg L− 1 at 22 ± 1 °C and acceptable water quality conditions. Samples were collected after 24 h and then every week interval for 9 weeks. Values of white blood cells (WBC) and lymphocyte in fish exposed to diazinon (group B) were significantly lower than unexposed group (group A) while, the level of neutrophils was higher (P < 0.05). No significant differences were found in values of monocytes, eosinophils and immature neutrophils between these two groups (P > 0.05). Also, values of WBC and neutrophils in intraperitoneally glucan injected fish (0.3 mg/kg body weight intraperitoneally as a single dose) plus diazinon bath (group D) were lower and higher than glucan received fish without diazinon bath (group C), respectively (P < 0.05). Lymphocyte, monocyte and immature neutrophils values in group D were also higher than group C for the first 7, 14 and 28 days post-exposure, respectively and then they reduced to lower levels than group C during the rest of the experiment. Also, level of eosinophils in group D was lower than group C (P > 0.05). The level of lysozyme in liver and kidney tissues of group B was significantly and insignificantly higher (P < 0.05) than group A for 4 weeks post-treatment and then it reduced to lower levels until week 9 post-exposure. The levels of lysozyme in spleen and serum were also, significantly and insignificantly higher in group B than group A for the first 3–4 weeks post-exposure and, then they reduced to below the levels measured during the rest of the experiment (P > 0.05). There was no significant difference in the lysozyme contents of liver, kidney, spleen and serum between groups C and D (P > 0.05). Mean spontaneous CL response in groups B and D was significantly lower than groups A and C throughout the experiment (P < 0.05). Maximum peak of CL response was found in group C for 5 weeks post-exposure, while the minimum peak was found in group B throughout the experiment. Also, peak of CL response in group D was almost similar to that of group C up to 2 weeks post-exposure, but it significantly reduced to lower level than group C during the rest of the experiment.