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3C - Fate and effects of TBT (WEP/174) Inhibition of gonadal steroidogenesis in catfish by tributyltin (TBT) in vitro. Rurangwa, Eugene1, Willems, Patricia1, McAllister, Brian2, Kime, David2, Ollevier, Frans1, 1 Katholieke Universiteit Leuven, Leuven, Belgium2 The University of Sheffield, Sheffield, United Kingdom ABSTRACT- Organotins are still present in aquatic environments from the past use of tributyltin-containing antifouling paints before recent regulations prohibited their use on small boats. In addition, their widespread application as biocides in protection of wood, wall paints and textiles provides an overlooked potential contamination source which can affect both humans in the workplace and aquatic organisms after their release in municipal wastewater and sewage sludge. The possible ecotoxicological impact of tributyltin (TBT) is therefore still of concern. In early studies, TBT was best known as an endocrine disruptor through its action in inducing imposex in marine gastropods. However, contrary to some marine species, much less is known about the impact of TBT to freshwater fish species. Recent advances in aquatic ecotoxicology have focussed on the detection of specific effects of environmental pollutants on fish gametes to study the impact of pollution on fish reproduction and have shown that TBT at environmental concentrations significantly decreased the motility of fish spermatozoa and reduced the activity of some enzymes involved in energy metabolism. The present study has investigated its effects on gonadal steroidogenesis in vitro using the African catfish (Clarias gariepinus) as a fish model. Our results confirmed the evidence of TBT being an aromatase inhibitor. The results have also shown that TBT significantly affects the process of final gamete maturation leading to spawning in fish. At environmentally realistic concentrations as low as 0.1 ppb, TBT inhibited the Cytochrome P450 aromatase enzyme which catalyses the conversion of testosterone to estradiol in catfish ovaries in vitro. The production of 17,20beta-dihydroxy-4-pregnen-3-one (17,20betaP), a progestogen important during the final maturation of gametes, was inhibited at 0.01 ppb TBT in catfish sperm. Key words: aromatase, Tributyltin, steroidogenesis, catfish |
