Molecular Mechanism Of Reproductive Toxicity Induced By Beta-cypermethrin In Zebrafish

Beta-cypermethrin,a type II synthetic pyrethroid insecticide,is widely used in household hygiene and agricultural production due to its low production cost,simple process and long lasting time.Due to the large amount of use,it remains in various environmental media such as air and water bodies,posing a threat to the health of nontarget organisms.In addition,beta-cypermethrin is highly toxic to aquatic organisms.Several studies have demonstrated that beta-cypermethrin can affect the reproductive system of mammals.However,there is still a scarcity of information about the reproductive toxicity to fish induced by beta-cypermethrin and its molecular mechanism.Therefore,this study used zebrafish as a model to explore the reproductive toxicity of beta-cypermethrin to aquatic organisms and the related molecular mechanism.In this study,the adult zebrafish(three-month old)were exposed to 0,0.1,0.5 and 2.5 ?g/L beta-cypermethrin for 21 days.The reproductive toxicity of beta-cypermethrin to zebrafish was comprehensively evaluated according to the 21-day cumulative egg production,the histological changes in gonad,the content of 17?-estradiol(E2)and testosterone(T),in plasma,and the transcriptional levels of hypothalamic-pituitarygonadal(HPG)axis related genes.The main results were described below.1.A decrease in cumulative egg production of zebrafish was observed,indicating that beta-cypermethrin had a negative impact on reproductive capacity of zebrafish and had reproductive toxicity to zebrafish.2.Histological analysis of gonads showed that the proportion of early oocytes and spermatocytes increased significantly after exposure to beta-cypermethrin,while the proportion of mature oocytes and spermatocytes decreased significantly.This indicated that beta-cypermethrin inhibited the gametogenesis of zebrafish.3.After exposure to beta-cypermethrin,the content of E2 and T of female zebrafish decreased significantly in the 2.5 ?g/L exposure group,and the content of T in male zebrafish of each exposure group decreased significantly.It showed that cypermethrin can interfere with the secretion of zebrafish sex hormones.4.Further exploration showed that,the transcription levels of HPG axis related genes were remarkably changed,which corresponded well with the alterations of hormone levels.This indicated that beta-cypermethrin may affect hormone levels by regulating HPG axis expressionThese results demonstrated that beta-cypermethrin might have adverse effect on reproductive system of zebrafish through delaying gametogenesis,disturbing sex hormone secretion,and affecting HPG axis gene expression.This experiment provided a reference for evaluating the toxic effects of pyrethroids on aquatic organisms and the use of beta-cypermethrin in fishery production.