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(T/FF222) The Effect of Temperature on Sexual Differentiation and Development in the Zebrafish, Danio rerio.. Vaughan, Martin1, van Egmond, Roger1, Tyler, Charles2, 1 2 ABSTRACT- A major global effort is underway to develop ecotoxicity test guidelines for the hazard assessment of endocrine disrupters (EDs). Sexual development and reproduction in fish have become key endpoints in the assessment of chemical hazards in the aquatic environment. Sex determination and differentiation, however, are often labile in fish and can be altered not only by the use of hormones, but in certain species, also by alterations in the physical environment (e.g. temperature). Thermal manipulation has been used to alter sex in a variety of teleosts, including members of the Cyprinidae family. The zebrafish (Danio rerio), is recommended for use in chronic toxicity tests by OECD, yet we know little about the environmental control of sexual differentiation in this species. To enable us to use reproductive endpoints, such as sexual differentiation and development, with confidence in ED tests, there is a need to fully understand the control of these processes. Previous investigators have observed the occurrence of juvenile hermaphroditism in the zebrafish, where the gonads start to differentiate as ovaries 10-12 days after hatching, irrespective of the sex. Subsequently, half continue to develop as ovaries, but half transform into testes, when the fish reach 23-25 days post hatch. The whole process of sexual differentiation is normally complete by 40 days post hatch, when there is a 1:1 sex ratio, (at 25-26 oC). In the current study we investigated the effect of three temperatures (23, 28 and 32 oC) on sexual differentiation and development in the zebrafish. The findings are discussed with reference to the natural variability in fecundity in this species observed in our laboratory. Key words: zebrafish, sexual differentiation/development, endocrine disrupters, temperature |
