Effects of experimental poisoning with chlorpyrifos on non-specific immunity and disease resistance to aeromonasis infection in rainbow trout (Oncorhynchus mykiss)

Organophosphate pesticides are one of the chemical pollutants of surface water, which may increase the susceptibility to disease in fishes.Therefore, in the present experiment, the effects of subacute chlorpyrifos poisoning on immune system function and disease resistance of rainbow trout to aeromonasis infection was evaluated. Numbers of 180 fish with an average weight of 42 g were divided between 4 experimental groups (3 replicates) control, low dose (2.5 μg/L), middle dose (5 μg/L) and high doses of chlorpyrifos (10 μg/L) and they were subjected by the above treatments for 10 days. At the end, blood samples were taken to measurement of haematological and immunological parametersand fishes were subjected to bacterial challenge by intraperitoneal injection of lethal dose of Aeromonas hydrophyla for 14 days. Evaluation of haematological parameters showed a significant decrease in the number of white blood cells, red blood cells, haematocrit, haemoglobin and the percentage of blood lymphocytes in fish treated with highest dose of chlorpyrifos (P<0.05).The evaluation of blood immunity index also showed a significant reduction in total immunoglobulin, lysozyme, complement, total protein, albumin and globulin in the highest dose of chlorpyrifos (P<0.05).The cumulative mortality rate of fish in the challenge with Aeromonas hydrophila showed a direct correlation with the increase in chlorpyrifos dose, but only the highest dose group compared with the control group showed a significant difference (P<0.05).According to the results of this experiment, it is concluded that increasing the environmental concentration of chlorpyrifos has harmful effects on the defense system of rainbow trout and decreases its resistance to bacterial pathogens.