Effects of High Concentrations of Flumequine on CYP Gene Expression and Histopathology in Olive Flounder, Paralichthys olivaceus

Flumequine is an antibiotic that is used to treat bacterial diseases in aquaculture. Fish express drug-metabolizing genes in response to antibiotic exposure. However, studies on the effects of high flumequine concentrations on drug metabolism genes and histopathology of the olive flounder are limited. To investigate the response of olive flounder to flumequine, we administered it at different concentrations. We analyzed the expression of drug metabolism genes (<i>CYP</i>) in the liver and histopathological lesions in the liver, spleen, and kidneys. The gene expression levels of <i>CYP</i> were higher at the highest flumequine concentration tested (4×) than at the lowest flumequine concentration (1×). The highest <i>CYP</i> gene expression level was observed for <i>CYP</i>2B4 (46.6-fold) at 4× flumequine compared to that in the control group. Hepatic atrophy, lymphocytic infiltration, and hematopoiesis were observed in the liver, spleen, and kidney at 4× flumequine between 3 and 24 h compared to 1× flumequine, respectively. These results contribute to a better understanding of drug metabolism and the general toxicity of pharmaceutical exposure in olive flounder.