| Monocrotophos (MCP) is one of organophosphorous pesticides with high water solubility and showed environmental estrogen activity because it can induce the production of vitellogenin in male goldfish. Monocrotophos showed potential impact on human health and aquatic organism. There are many reports about the toxicity of monocrotophos. Exposure of monocrotophos is known to produce a variety of biochemical process and reproduction damnification in fishes. But very few reports about the effects of monocrotophos on sexual characteristics existed in the literatures. The guppy (Poecilia reticulate) was chosen as experimental animal for several reasons. Most importantly, it is a viviparous, readily available, and easily handled fish. It is a viviparous fish with a short reproductive period and with sperm count, body coloration, gonadal size, sexual behavior, and reproductive rate apparently independent of season. The guppy is sensitive to toxic compounds and suitable for toxicity study. So in this study, we use the guppy as a model organism to do a series of laboratory experiments. In a series of experiments, we have investigated the effects and mechanism of monocrotophos on sexual characters during sexual development. The results shed light on the further research on the environmental estrogen effect of monocrotophos. The results showed that:(1) Following exposure to monocrotophos(0.01,0.10,1.00 mg/L) for 90 days, the result of the western-blotting, using the polyclonal antibody of anti-goldfish VTG, showed that monocrotophos could induce male guppy to synthesize VTG, which has two main protein bands with relative molecular weights of 152kDa and 135kDa, respectively. The results proved that monocrotophos have environmental estrogen activity further.(2) The effects on prima sex traits in guppy altered significantly after exposure to monocrotophos. After exposure to monocrotophos of various concentration(0.01, 0.10,1.00 mg/L) for 90 days, the development of gonad was delayed. The GSI of guppies in 0.10 and 1.00 mg/L monocrotophos decreased significantly than that of control. In the control and treated guppies which were exposed to 0.01, 0.10, 1.00 mg/L monocrotophos, the gonopodium length were 0.518±0.036,0.475±0.030,0.471±0.029,0.476±0.033cm, and the counts of sperm cells were 3.43±0.94,2.57±0.68,2.06±0.43,2.00±0.49millions. The gonopodium length and counts of sperm cells decreased significantly. Following exposure to monocrotophos(0.01,0.10,1.00 mg/L) for 90 days, the counts of oocytes and embryos of females decreased significantly than that of control. The guppy embryos exposed to monocrotophos become malformation and heteroplasia which induce counts of offspring and the hatching rate reduces. The content of testosterone in testis decreased gradually with the increase of monocrotophos concentration, while the 17β- estradiol increased. It is suggested that the maladjustment of gonadal hormone may induce prima sex traits impairment in guppy.(3) The effects on second sexual characters in guppy altered significantly after exposure to monocrotophos(0.10,1.00 mg/L)for 90 days. The carotenoid content of male skin was significantly reduced by exposure to 0.10, 1.00mg/L concentrations of monocrotophos, which made coloration index of male skin decreased. In the control and treated guppies which were exposed to 0.01, 0.10, 1.00 mg/L monocrotophos, the coloration index were 33.65±0.05%,30.74±0.05%,28.12±0.04%,26.00±0.05% respectively. Following exposure to monocrotophos(0.10,1.00 mg/L) for 90 days, the coloration index reduced markedly. The counts of melanophores decreased while tyrosinase activity did not change. The ultrastructure of the skins in male guppy was performed using the Transmission Electron Microscope (TEM). The pigment cells consist of melanophores and iridophores. The melanophores in the normal skins of normal distribute closely and include many melanin granules. The content and structure of melanophores in the skin of guppy exposured with monocrotophos were dramatically different from those in normal skin. The results show that the melanophores degenerated in the skin of guppy exposured with monocrotophos. Monocrotophos induced dissolution of nuclear membrane of the melanophores and iridophores cell. Monocrotophos also dissolve membrane of the pigment cells. It is supposed that the maladjustment of gonadal hormone, the decrease of carotenoid content in male skin and the damnification of structure in the skin induced the second sexual characters markedly female biased after exposure to monocrotophos. In order to receive the purpose, we use the guppy (Poecilia reticulata) as a model organism to do a series laboratory experiments. The selected biomarkers include the ultrastructure of skin and the counts of sperm cells, oocytes and embryos (cell level), coloration and gonadal weight (organ level) and the sexual maturation of juveniles and their later reproductive capability as adults (population level). Finally, it is concluded that monocrotophos made the maladjustment of gonadal hormone leading to prima sex traits impairment and second sexual characters markedly female biased.
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