The teratogenic effects of methylmercury on early development of the zebrafish, Danio rerio

Chronic bioassays were used to evaluate the concentration and exposure dura tion of methylmercury that resulted in specific teratogenic defects in Dani o rerio embryos exposed at different developmental stages. Embryos in diffe rent stages of development (cleavage, blastula, gastrula, or segmentation) were exposed to 20 or 30 mu g/l of methylmercuric chloride (CH3HgCl) for va rious exposure durations (8, 16, 32 h, or continuously to hatching). These exposures frequently caused two morphological defects, tissue abnormality i n the median finfold and a flexure of the posterior tail region. The critic al period of exposure for the production of both effects begins around 18-2 0 h after fertilization, with increased exposure resulting in more severe e ffects. These critical periods coincide with both tail and median finfold f ormation. (C) 2000 Elsevier Science B.V. All rights reserved.