ToxSci Advance Access published online on January 6, 2007
Toxicological Sciences, 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
* Department of Environmental Toxicology and Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, Texas 79409-1160, USA
U.S. Geological Survey Texas Cooperative Fish and Wildlife Research Unit and Departments of Range Wildlife and Fisheries Management and of Biological Sciences, Texas Tech University, Lubbock, Texas 79409-2120
2 To whom correspondence may be addressed: Reynaldo Patiño, USGS Texas Cooperative Fish & Wildlife Research Unit, Texas Tech University, Lubbock, TX 79409-2120, USA, Phone: 806-742-2851 ; 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 6 additional weeks. Eight females in each tank replicate (n = 3) were paired weekly with 4 males from the same respective treatment, and packed-egg (spawn) volume (PEV) was measured each of the last 5 weeks. At least once during weeks 14 to 16 of exposure, other endpoints measured included fertilization rate, fertilized egg diameter, hatching rate, standard length and craniofacial development of 4-day-postfertilization larvae, and TH 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 towards 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.