The use of pesticides to eliminate pests and weeds has raised concerns about water pollution and adverse effects on aquatic organisms, so many efforts have been made to increase the resistance of fish to these pesticides by using a proper nutrition strategy. Therefore, the aim of this study is to investigate the growth performance, antioxidant, and immune responses of fish exposed to Imidacloprid insecticide (C9H10ClN5O2) by different doses of Chlorella vulgaris dry powder to the diet of common carp (Cyprinus carpio). In this study, 600 common carp with a medium weight (18.10±0.2 g; mean ± SE) were prepared and after adaptation and determination of lethal concentration of Imidacloprid, for 56 days in 6 treatments and each with 3 replications were classified and tested (Control (T1), 5% Chlorella vulgaris dry powder and no pollution (T2), 10% Chlorella vulgaris dry powder and no pollution (T3), No Chlorella vulgaris dry powder and 12.5% LC50 Imidacloprid (T4), 5% Chlorella vulgaris dry powder plus 12.5% LC50 Imidacloprid (T5) and 10% Chlorella vulgaris dry powder plus 12.5% LC50 Imidacloprid (T6)). After 96 hours of exposure to distinct concentrations of the insecticide, the total mortality was measured and the Imidacloprid median lethal concentration (LC50) over 96 hours was calculated (266.2 mg/l) using Probit analysis. According to the result, common carp fed T2 had the highest final weight (FW), weight gain (WG), and specific growth rate (SGR), and the lowest feed conversion ratio (FCR) among the groups (P<0.05). Fish in the T2 group had the highest total proteins, albumin and globulin (P<0.05). Fish in the group T4 had the highest cortisol, lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) levels in the blood, while fish fed T2 and T3 had low values (P<0.05). The alternative complement pathway (ACH50) was significantly higher in T2 and T3 than other groups (P<0.05). Blood total immunoglobulin (Ig) and lysozyme activity were high in T2 and T3 groups, and had the lowest values in the T4 group (P<0.05). The superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) showed the highest activities in T2 (P<0.05). T4 group had the highest malondialdehyde (MDA) level, while T2 and T3 groups had the lowest MDA level (P<0.05). The highest amylase, protease and lipase were in the T2 group, while the lowest values were in the T4 group (P<0.05). In conclusion, dietary Chlorella vulgaris protects common carp from Imidacloprid insecticide, since it improved growth performance, antioxidant and immune responses of fish.
