Effects of Dietary Cerium Oxide Nanoparticles on Growth Performance, Plasma Biochemistry, and Histopathological Changes of <i>Cyprinus Carpio</i> Koi Fish Exposed to Florfenicol Antibiotic

This study was conducted to investigate the effects of dietary cerium oxide nanoparticles (CeO 2 ‐NPs), on growth performance, plasma biochemistry and histopathological changes of koi fish ( Cyprinus carpio koi) exposed to florfenicol (FF) antibiotic in a 60‐day experiment. The fish with an average weight of 2.38 ± 0.44 g were completely randomly distributed into six different groups with three replications. The experimental groups included: Basal diet without additives (control), basal diet + oral antibiotic, basal diet + antibiotic bath, basal diet supplemented with CeO 2 ‐NPs, basal diet supplemnted with CeO 2 ‐NPs + antibiotic bath, and basal diet supplemented with CeO 2 ‐NPs + oral antibiotic. The experimental unit was a glass aquarium with a capacity of 110 L of water and 10 fish were stocked in it. At the end of the experimental period, growth performance of fish, blood plasma indices, and histopathology of liver, kidney, gill, and intestine were investigated. The results showed that the final body length of the fish in the basal diet + antibiotic bath group was significantly higher than the control group and the basal diet supplemented with CeO 2 ‐NP + oral antibiotic group ( p &lt; 0.05). Histological studies showed that the kidney, liver, and intestinal lesions of fish in different groups did not differ microscopically. In gill tissues, changes in secondary lamellae and their destruction occurred in different parts of the primary lamellae in different groups, but overall, no differences were observed among the different groups. The plasma aspartate transaminase (AST) and alanine transaminase (ALT) levels were significantly decreased in all groups compared to the control ( p &lt; 0.05), except the basal diet supplemented with CeO 2 ‐NPs + antibiotic bath group. The plasma blood urea nitrogen (BUN) level decreased significantly in the basal diet supplemented with CeO 2 ‐NPs + antibiotic bath group compared to the control, while this value increased in the basal diet + oral antibiotic and the basal diet supplemented with CeO 2 ‐NPs + oral antibiotic groups compared to the control ( p &lt; 0.05). The results of this study revealed that adding CeO 2 ‐NPs to the basal diet at level of 0.8 mg/kg decreased the alkaline phosphatase (ALP), AST, and ALP levels in plasma of koi fish compared to the control ( p &lt; 0.05). The simultaneous administration of dietary CeO 2 ‐NPs with the bath and oral FF antibiotic increased the AST and ALT levels and the BUN level in plasma, respectively ( p &lt; 0.05).