This study aimed to investigate the effects of benzo[a]pyrene (BaP) on immune status of orange spotted grouper (Epinephelus coioides). Fish were injected with 2, 20 and 35 mg/kg-bw of BaP and were kept under laboratory conditions for 14 days. Blood samples were taken at days 1, 4, 7, and 14 and changes in total WBC and RBC, phagocytosis, lysozyme activity, lysosomal membrane stability, immunoglobulin M (IgM) level and antibacterial activity were evaluated. Also BaP bioaccumulation in fish muscle was measured. BaP concentration in the muscle of treated fish reached a maximum level after 4 days (P < 0.05). Exposure of fish to BaP resulted in a significant decrease of total RBC and WBC, lysozyme activity, lysosomal membrane stability, IgM level and antibacterial activity after 4 days and phagocytosis after 7 days of the experiment (P < 0.05). Totally, the results revealed BaP ability to suppress the fish immune function.
