ToxSci Advance Access originally published online on January 6, 2007
Toxicological Sciences 2007 96(2):246-254; doi:10.1093/toxsci/kfm001
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Published by Oxford University Press 2007.
Effects of Prolonged Exposure to Perchlorate on Thyroid and Reproductive Function in Zebrafish
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* Department of Environmental Toxicology, Texas Tech University, Lubbock, Texas 79409-1160
U.S. Geological Survey Texas Cooperative Fish and Wildlife Research Unit
Department of Range Wildlife and Fisheries Management
Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409-2120
2 To whom correspondence should be addressed. Fax: (806) 742-2946. E-mail: reynaldo.patino{at}ttu.edu.
Received October 27, 2006; accepted January 3, 2007
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Abstract |
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The objectives of this study were to determine the effects of prolonged exposure to perchlorate on (1) thyroid status and reproductive performance of adult zebrafish (Danio rerio) and (2) F1 embryo survival and early larval development. Using a static-renewal procedure, mixed sex populations of adult zebrafish were exposed to 0, 10, and 100 mg/l nominal concentrations of waterborne perchlorate for 10 weeks. Thyroid histology was qualitatively assessed, and females and males were separated and further exposed to their respective treatments for six additional weeks. Eight females in each tank replicate (n = 3) were paired weekly with four males from the same respective treatment, and packed-egg (spawn) volume (PEV) was measured each of the last five weeks. At least once during weeks 14–16 of exposure, other end points measured included fertilization rate, fertilized egg diameter, hatching rate, standard length, and craniofacial development of 4-day–postfertilization larvae and thyroid hormone content of 3.5-h embryos and of exposed mothers. At 10 weeks of exposure, perchlorate at both concentrations caused thyroidal hypertrophy and colloid depletion. A marked reduction in PEV was observed toward the end of the 6-week spawning period, but fertilization and embryo hatching rates were unaffected. Fertilized egg diameter and larval length were increased by parental exposure to perchlorate. Larval head depth was unaffected but the forward protrusion of the lower jaw–associated cartilage complexes, Meckel's and ceratohyal, was decreased. Exposure to both concentrations of perchlorate inhibited whole-body thyroxine content in mothers and embryos, but triiodothyronine content was unchanged. In conclusion, prolonged exposure of adult zebrafish to perchlorate not only disrupts their thyroid endocrine system but also impairs reproduction and influences early F1 development.
Key Words: perchlorate; thyroid; reproduction; embryo; larvae; development; fish.
1 Present address: Department of Embryology, Carnegie Institution of Washington, Baltimore, MD 21218.