Biochemical and histological alterations in adult zebrafish（Danio rerio）ovary following exposure to the tetronic acid insecticide spirotetramat.

As a new tetronic acid derivative insecticide, spirotetramat has been reported to be toxic to an array of aquatic organisms. However, the toxic effects of spirotetramat on zebrafish especially at ovary are still obscure. Hereby, the acute toxicity of spirotetramat towards zebrafish（Danio rerio），as well as the changes on biochemical and histological traits of ovary were investigated. The acute toxicity test results showed that the median lethal concentration (LC) value of spirotetramat were 9.61 mg/L and 7.21 mg/L at 72 h and 96 h, respectively, suggesting spirotetramat has moderate toxicity to zebrafish. In the following sub-lethal toxicity test, the gene expression of superoxide dismutase (SOD), catalase (CAT), and gonadotropic hormone receptor (FSHR and LHR) together with the content of malondialdehyde (MDA) in ovary were measured at 14, 21, and 28 days after exposure to 36, 360 and 720 μg/L. Under high concentration treatment (360 and 720 μg/L), MDA content, the relative transcription CAT and SOD gene level increased significantly in ovary (p < 0.05). That indicated sub-lethal doses spirotetramat caused oxidative stress and lipid peroxidation in zebrafish ovary during the entire experimental period. Under the exposure to spirotetramat at 720 μg/L after 14 days, the relative transcript FSHR gene level was down regulated, and the relative transcript LHR gene level was up regulated. Moreover, spirotetramat affected the oocyte development especially on the diameter size and maturation during the ovary tissue biopsies at 28 days. Taken together, these findings revealed the adverse effects of spirotetramat on fish from the biochemical and histological aspects.