Influences Of Rare Minnow (Gobiocypris Rarus) To Exposure Of 17α-Methyltestosterone And Bis(Tributyltin) Oxide

The experiment was conducted to evaluate the impact of environmental endocrine disruptors, 17α-Methyltestosterone and Bis(tributyltin)oxide, on biology of rare minnow (Gobiocypris rarus). The fish, at different life stages, was exposed to 17α-Methyltestosterone and Bis(tributyltin)oxide, at concentration levels closed to environmental conditions. Embryonic development, growth, hispathology and vitellogenine analysis was used to investigate endocrine disruption effect and biotoxicity of 17α-Methyltestosterone and Bis(tributyltin)oxide, and comparative sensitivity of the fish at different life stages.Water flow through controlled system and the exposure system was set up in laboratory simulating natural environment. For the sake of accuracy, the materials and equipment were made pollution free in accordance with endocrine disruptor's bioassay standard of US Environmental Protection Agency. The culture methodology of rare minnow was established according to laboratory scale, which provided a system enough for fish toxicology experiments. The relevant conditions were adjusted so as to assure the accuracy and reliability of results.The results of present research endeavor reveal that 17α-Methyltestosterone has no toxic effect upon the embryonic development of rare minnow. During experimental exposure, fish embryo developed normally and no embryonic mortality was observed. At sexual differentiation stage and fry-to-fish stage of rare minnow, 17α-Methyltestosterone showed androgenetic effect and promoted gonad development. Plasma vitellogenin was induced during sexual differentiation stage at exposure concentration higher than 50ng/L. It may have been caused due to conversion of 17α-Methyltestosterone into 17α-Methylestradiol, which showed estrogen effect. The growth of rare minnow was not affected and there was no cytotoxicity in hepatic, renal and gill tissues after exposure to 17α-Methyltestosterone. Increased exposure concentration of 17α-Methyltestosterone showed a negative impact on the plasma vitellogenine contents of adult female fish. Vitellogenine synthesis was suppressed due to endocrine disruption effect of 17α-Methyltestosterone but with no impact on the growth of adult fish.The results of exposure to Bis(tributyltin)oxide showed that also, there was no endocrine disruption and biotoxicity observed at embryonic development stage of rare minnow. The embryo development was not inhibited, and no embryo mortality was observed. All the embryos developed normally. At sexual differentiation stage and fry-to-fish stage of rare minnow, Bis(tributyltin)oxide showed androgen effect spermary development of the fish was promoted. The epithelial cells of gills and nephric tubules proliferated and showed hypertrophic growth. In adult fish, at exposure concentration higher than 16ng/L, hepatic tissues showed lesions and hepatic cells were found to be vacuolar. The results indicate that Bis(tributyltin)oxide had a strong biotoxic impact upon the fish tissues. Vitellogenine synthesis and growth of the fish were not affected throughout the exposure duration.Comparative sensitivity at different life stages of rare minnow to exposure of environmental endocrine disruptors, 17α-Methyltestosterone and Bis(tributyltin)oxide, was different at every stage. Sexual differentiation stage of rare minnow was found to be the most sensitive stage, followed by the fry and adult stage. Sensitivity of embryonic development stage of rare minnow to exposure of environmental endocrine disruptors was not significant. Hepatic and gill tissue were badly affected by the exposure to Bis(tributyltin)oxide concluding that these tissues could be used as test specimen to investigate the biotoxic effect of exposure to environmental endocrine disruptors.