Evaluation of Chlorpyriphos as an Organophosphate Pesticide on Hematology, Blood Biochemistry, Antioxidant Capacity, Oxidative Stress, and Histopathological Changes in Juvenile Silver Barb ( <i>Barbonymus gonionotus</i> )

The freshwater fish population in Bangladesh is adversely affected by the use of pesticides in agriculture. Furthermore, pesticide consumption is increasing daily due to the introduction of high‐yielding crop varieties. This study aimed to examine the impact of the organophosphate pesticide chlorpyriphos on various pathological alterations and acute toxicity tests in juvenile silver barb ( Barbonymus gonionotus ). This was achieved by elucidating multiple biomarkers in a time‐ and dose‐dependent manner. Treatment of the fish with chlorpyriphos at a sublethal dose (0.005 ppm) compared to the control group led to changes in the hematopoietic parameters, organ‐specific histo‐morphologies, and enzymatic activities in fish. Among the notable abnormalities were gill clubbing, missing gill lamellae, hyperplasia, nuclear hypertrophy, vacuolation, glomerular expansion, increased renal tubular width, hemorrhage, necrosis, and pyknosis in fish. Large lymphocytes, dead cells, fused cells, binucleated cells, tear‐shaped cells, ghost cells, senile cells, and aberrant cell shapes in peripheral nuclear erythrocytes were also observed. Impact of chlorpyriphos in silver barb exhibited a significant decrease in the parameters such as hemoglobin (g/dL), hematocrit/packed cell volume (PCV) (%), red blood cell (× 10 6 mm 3 ), white blood cell (× 10 3 /mm 3 ), mean corpuscular hemoglobin concentration (%), and blood glucose level (nmol/L). However, the mean cell volume (µm 3 ) and mean cell hemoglobin (pg) counts exhibited an opposite order. Furthermore, fish exposed to chlorpyriphos enhanced the serum glucose, glutamic pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), indicating liver toxicity in fish; however, brain acetylcholinesterase enzyme activity was significantly reduced than in the control, indicating neurodegeneration in fish. The superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S‐transferase (GST) were examined as critical components of the antioxidant defense system in a time‐dependent manner relative to the control group. It can be stated that organophosphate pesticides produce oxidative stress, resulting in the generation of free radicals and alterations in antioxidants, oxygen free radicals, the scavenging enzyme system, and lipid peroxidation. Overall, the results demonstrated that the chlorpyriphos pesticide negatively affected the enzymatic activities, hematology, and organ‐specific histology in juvenile silver barb.