Serum and ultrastructure responses of common carp (Cyprinus carpio L.) during long-term exposure to zinc oxide nanoparticles

The uptake of nanoparticles by aquatic organisms such as fish has raised concerns about the possible adverse effects of nanoparticles (NPs). In this study, we aimed to evaluate the toxicological effects in juvenile common carp exposed to zinc oxide nanoparticles (ZnO-NPs) for 12 weeks. The carp were exposed to 0 (control), 0.1, 0.3, 0.8, and 2.4mg/L of ZnO-NPs under a flow-through exposure system. Fish were sampled at 0, 4, 8, and 12 weeks to test for zinc in the test water and blood, and biochemistry analysis; further, they were sampled at 12 weeks to observe ultrastructural changes in the liver, kidney, and gill. In the organic serum, changes in the glutamic pyruvic transaminase/alanine aminotransferase (GPT/ALT) and glutamic oxaloacetic transaminase/aspartate aminotransferase (GOT/AST) levels were significant, but changes in the lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) levels were not significantly different across all exposure periods. In the inorganic serum, the magnesium (Mg), inorganic phosphorus (IP), sodium (Na(+)), and chloride (Cl(-)) levels were significantly different in the exposure group and across exposure periods. However, calcium (Ca) and potassium (K(+)) levels were not significantly different. In the enzyme serum, the glucose (GLU) level significantly increased for the highest exposure group, but the total cholesterol (TCHO), triglyceride (Tg), and total protein (TP) levels were not significantly different during the exposure period. Ultrastructural changes in the liver induced changes in the black granules (of various sizes) in the lysosomes, indistinct nucleus membrane, and non-spherical nucleus. In the kidney, some mild changes were observed in the size and number of the lysosomes in the renal tubule. Desquamation and hypertrophy of pavement epithelial cells and vacuolation in the cytoplasm of the chloride cells were observed in the gill. Nanoparticles were also observed in the red blood cells, cytoplasm of all tissues, and glomerulus of the kidney. The observed changes in the serum and tissues may provide useful information regarding environmental conditions and risk assessments of aquatic organisms.