Antiparasitic effects of copper nanoparticles on monogeneans Dactylogyrus spp. in Cyprinus carpio koi associated with physiological and histological alterations.

This study investigated the antiparasitic effects of copper nanoparticles (CuNPs, 44.33 nm) and their influence on hematological, ionic, and gill histological parameters of Cyprinus carpio koi. A total of 240 fish were distributed into four experimental groups: control (no copper exposure) and three groups treated with CuNPs (0.3, 0.6, and 1.25 mg/L) for 5 h. After exposure, some individuals were maintained for 48 h to evaluate potential reinfection and physiological alterations. Exposure to CuNPs significantly reduced infestation by Dactylogyrus minutus and Dactylogyrus extensus, particularly at 1.25 mg/L. After 48 h, an increase in total erythrocytes, leukocytes, lymphocytes, and neutrophils was observed in the groups exposed to 0.6 and 1.25 mg/L CuNPs, along with a reduction in hematocrit and mean corpuscular volume (MCV). Plasma chloride levels were most affected in the groups exposed to 0.6 mg/L at 5 h and 0.3 mg/L at 48 h, while calcium showed a significant reduction over time. Histological analyses revealed gill lesions such as lamellar congestion, lamellar fusion, eosinophilic and mononuclear inflammation, hyperplasia, and necrosis, which were more evident after 5 h of exposure and reduced after 48 h of CuNPs exposure. Despite the antiparasitic efficacy of CuNPs, their physiological effects require further studies to determine safe therapeutic doses for controlling monogeneans in this host fish.