| Triadimefon, a triazole fungicide, has been widely detected in the environment, but few studies have assessed its effect on aquatic organisms. The present study evaluated the effect of triadimefon in embryo-larval stages of zebrafish. Zebrafish embryos exhibited teratogenic evidence of bent spine, uninflated swim bladder and other malformations after being exposed to various triadimefon concentrations (2-4μg/mL) from 6 to 120 h post-fertilization (hpf). Locomotor activities namely spontaneous movement in embryos and swimming activity in larvae were detected to assess the neurotoxicity. This was the first study to detection the neurotoxicity and teratogenic of triadimefon in zebrafish. It seemed that the spontaneous movement was related to the hatching rate and the potential course of the uninflated swim bladder. The results suggested that the need for additional research to identify the mode of triadimefon toxicity.The study evaluated thyroid hormone levels and the expression of related genes in the hypothalamic-pituitary-thyroid (HPT) axis, including thyroid-stimulating hormone (TSHP), deiodinases (D1 and D2) and the thyroid hormone receptor (TRαand TRβ). After triadimefon exposure, increased T4 but decreased T3 were found. It seemed that increased TSHβcould result in increasing T4. The conversion of T4 to T3 occurred by the deiodinases. Decreased T3 could be explained by decreasing deiodinase type I (D1). The action of thyroid hormones was mediated by their binding to nuclear receptors that acted directly on target genes. TRP mRNA levels were significantly down-regulated, possibly as a response to the decreased T3 levels. The overall results indicated that triadimefon exposure could alter gene expression in the HPT axis and that mechanisms of disruption of thyroid status by triadimefon could occur at several steps in the synthesis, regulation, and action of thyroid hormones.Impact of triadimefon on endocrine reproductive system in zebrafish, including vitellogenin (Vtg) mRNA, mortality rate, growth, sex ratio, gonad histology and sperm parameters was evaluated in this study by using full life cycle test. Zebrafish of 24 hours post fertilization (24 hpf) were exposed to various concentration of triadimefon (0.125,0.25,0.5μg/mL) until 120 days. Increased mortality rate were observed in fish exposed to 0.5μg/mL triadimefon. At 40 dpf, Vtg mRNA expression was decreased in fish exposed to 0.25 and 0.5μg/mL triadimefon. Histological assessment revealed that the female fish in the treated by 0.5μg/mL triadimefon had immature ovaries. The sex ratio had a significantly increased in terms of males. These effects were consistent with aromatase inhibition. Armatase inhibitor could block the balance of estrogens and androgens so as to increase proportion of males in populations.F0 Breeding studies revealed significant reproductive dysfunctions in 0.25 and 0.5μg/mL triadimefon-treated groups. This was a report about fish with reduced reproductive capacity following exposure to triadimefon, had not been published yet. Reproductive success was a very complicated process and it might be influenced by multiple factors. The sperm examination revealed that triadimefon decreased the sperm mobility and sperm concentration, which could partially explain why the triadimefon-treated males were almost infertile. Then some parameters of the offspring F1 were tested, including embryo fertility, mortality, hatching rate and teratogenic effects. It suggested that triadimefon could adversely affect the fertility rate, the hatching and mortality. Decreaed fertily could be explained by decreasing sperm concentration and motility.0.125μg/mL and 0.25μg/mL triadimefon had no significantly influences on the fertility, hatching and mortality. Whether these concentrations had any other toxic effects needed to be illustrated in further study.
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