Thyroid development in larval lake sturgeon (Acipenser fulvescens) and the potential thyroid disruption associated with exposure to the organophosphate pesticide chlorpyrifos
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The thyroid hormone system plays a major role in larval development, growth, and metabolism in fish. Therefore, any anthropogenic alteration in thyroid function could have dramatic effects on individual fitness. In this study Lake Sturgeon, Acipenser fulvescens, larvae were exposed to a commercially used organophosphate pesticide, chlorpyrifos (0, 5, 500 and 2000ng/L), from hatch until the onset of exogenous feeding (~12 days at 14C). The presence of thyroid follicles was first observed at 6 days post hatch (dph). Molecular expression of thyroid receptor α (TRα) increased from 3 to 12dph and then decreased from 12 to 21dph. TRα expression was also significantly higher in brain, liver and muscle at 67dph when compared to TRβ. Of the circulating hormones only free-T3 was consistently measured in larval homogenates from all development time-points sampled. Exposure to chlorpyrifos had no effect on growth or thyroid follicle morphology during the course of the experiment.