| The environmental risk of organophosphorus pesticides (OP) increases rapidly with the improvement of the diversity and production of OPs. It has caused many environmental problems, such as the reproduction impairment, gonads alteration, the population decline, and so on. Monocrotophos (MCP), one of organophosphorous pesticides with high water solubility and environmental estrogen activity showed potential impact on human health and aquatic organism. So in this study, a full life cycle chronic toxicity experiment was performed by exposing zebrafish(Danio rerio) to 0.01,0.10 and 1.00mg L-1 MCP for two generation. Reproductive parameters such as the total number of eggs, the number of eggs in once spawns, the total number of spawning, the fertility and hatch in F0 (adult, exposed 28d ) and F1 (150d, exposed from fertility until adult to mating) were investigated. The induction of VTG, a widely used indicator for estrogenic exposure in fish, in the F0 male fish by 28d MCP exposure was determined by Western-blotting. In addition to the F0 gonads histopathological alterations were observed by light microscope and gametes by electron microscope, the reproduction effects of MCP on two generations of zebrafish were investigated as well. The results shed light on the further research on the environmental estrogen effect of MCP. The results are as follows:(1) The inhibition effect of MCP on the reproduction of zebrafish is not dose-dependent. Exposed in the 0.01, 0.10 and 1.00mgL-1 MCP, the zebrafish reproduction capacity represented a"U"-like curve. In other words, the reproduction suppression caused by 0.01 and 1.00mg L-1 MCP was less than that caused by 0.10mg L-1. 0.10mg L-1 MCP distinctly reduced the mate behaviors and the number of the offspring, but did not affect the fertility and hatch significantly. Moreover, the eggs,spawned by F1 female paired with normal male fish, showed a distinct reduction in the fertility and hatch rate (70.93% and 19.4% separately), implying a descending of the egg quality and an impact on the oogenesis by chronic exposure to MCP. (2) The F1 juvenile fish is highly sensitive to MCP. In the fist 30d of life cycle(hermaphrodite), the most sensitive stage for juvenile fish is 8-15d. The death rate of juvenile at this stage that live in the 1.00mgL-1 MCP is the highest, indicating that 1.00mgL-1 MCP has strong toxicity on the juvenile fish. The high death rate of juvenile may have the relationship with the population decline.(3) The result of the western-blotting, using the polyclonal antibody of anti-goldfish VTG, showed that MCP could induce male zebrafish to synthesize VTG, which has three main protein bands with relative molecular weights of 135kDa,107kDa and 96kDa, respectively. The protein bands of male fish exposed in 0.01 mg L-1 MCP is darker and wider than that of other samples, indicating that this concentration has the high VTG induction ability and strong endocrine disruption to male zebrafish. It is suggested that the high VTG induction in 0.01mg L-1 MCP exposed male fish may be related with the reproduction impairment.(4) The effects of MCP on the testis of mature male are examined. Spermatogonium, spermatocyte and the lobule membranes in the testis are swollen,. The electron micrographs of the sperms show that the membrane of the sperm cells, nucleus and the mitochondria are dropsical, fractional and dissolutive, as the phenomena of main damage effect of MCP.The vesicles that appear around some sperm cells may be the extravasated contents from the sperm cells. The most severe damage effect of MCP on the spermatogenesis is observed on the sperm cells from Spermatid to Spermmatozoon since the nucleus of these sperm cells could not completely contract and some even dissolved. The number of Sertoli cells increased and more sperm cells are incorporated into a Sertoli cells cytoplasm.(5) The effects of MCP on the oogenesis of mature female are also examined. The main effects on the early oocyte stage include the shrinkage of oocyte karyoplasm and the distortion of nucleolus. In vitellogenic oocytes peorid, it reveals the vitelline dissolution. The primary yolks decrease and secondary yolks coagulate. The nuclear membrane partly dissolution and fuse with karyoplasm or vitelline. The electron micrographs of the oocytes reveal that both of the early vitelline and late vitelline show dissolution and shrinkage. In the early of the expoursue peorid, part of zone radiata externa (ZRE) of egg shell breaks off and the zone radiata interna (ZRI) of egg shell becomes much thin with dissolution. On the contrary, in the late of the expoursue peorid, in the 0.10mgL-1 MCP, the ZRE fuse and the thickness of the ZRI resume, implying the protection activation in the concentration. The alteration of the eggshell thickness must affect the breeding success of the F1 female fish. It suggested the changes of eggshell structure have relationship with the reproduction impairment.
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