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	Figure 1. Sagittal view of zebrafish (Danio rerio) pituitary.
	Figure 2. Whole body weight and length of zebrafish (Danio rerio) after exposure to 0, 2.5, 10, 25, and 50 mg/L PTU. Measurements were performed with 60 animals after 35 days of exposure. Asterisks indicate significant differences between exposure and control groups (*P < 0.05, **P < 0.01; Dunn's test).
	Figure 3. Whole body contents of T4 in zebrafish (Danio rerio) exposed to 0, 2.5, 10, 25, and 50 mg/L PTU. Results are given as means ± SEM from three samples per replicate. Asterisks indicate significant differences between exposure and control groups (*P < 0.05; Dunn's test).
	Figure 4. Representative macroscopical pictures of the head region of zebrafish (Danio rerio) following exposure to 0, 10, 25, and 50 mg/L PTU. Increased red coloration due to blood aggregation in the opercular region (∗) at concentrations ≥10 mg/L and goiter formation (△) at concentrations ≥25 mg/L are clearly detectable.
	Figure 5. Representative histological pictures of thyroidal tissue in the control zebrafish (Danio rerio). The isolated thyroid follicles are distributed adjacent to the ventral aorta in the gill region. Follicular shape is spherical to oval with a cuboidal epithelium and a homogeneously stained colloid. Sections of 2 μm thickness stained with periodic acid-Schiff (PAS) and Mayer's hematoxylin.
	Figure 6. Representative histopathological effects in thyroidal tissue of zebrafish (Danio rerio) exposed to 25 and 50 mg/L PTU. Exposure to PTU resulted in massive hyperplasia and hyperemia with an increased number of small follicles embedded in adjacent blood capillaries (a, b). In the 25 and 50 mg/L concentration groups, inclusion bodies in the colloid were visible ((c): ▲). At concentrations ≥10 mg/L, severe hypertrophy of thyroid follicles could be detected with stratification and cell crowding (d): One individual in each of the 25 and 50 mg/L concentration groups showed mostly apically located vesicles in the epithelial cells ((e): ▲). Some individuals displayed small follicles scattered across the gills ((f): ▲). Sections of 2 μm thickness stained with periodic acid-Schiff (PAS) and Mayer's hematoxylin.
	Figure 7. Representative PAS-stained sagittal sections of zebrafish (Danio rerio) pituitaries exposed to PTU. The adenohypophysis is encircled by a dotted line to highlight the changes in the ratio between adeno- and neurohypophysis. A massive proliferation of PAS-positive cells (∗) mostly located in the proximal pars distalis is evident. PI—pars intermedia (adenohypophysis); PN—pars nervosa (neurohypophysis); PPD—proximal pars distalis (adenohypophysis); RPD—rostral pars distalis (adenohypophysis). Sections of 2 μm thickness stained with periodic acid-Schiff (PAS) and Mayer's hematoxylin.
	Figure 8. Pituitary surface areas of zebrafish (Danio rerio) after exposure to 0, 2.5, 10, 25, and 50 mg/L PTU. Measurements were performed with 60 animals after 35 days of exposure. Asterisks indicate significant differences between exposure and control groups (*P < 0.05,**P < 0.01, ***P < 0.001; Dunn's test).
	Figure 9. Ratio of adeno- to neurohypophyseal tissue of zebrafish (Danio rerio) after exposure to 0, 2.5, 10, 25, and 50 mg/L PTU. Measurements were performed with 60 animals after 35 days of exposure. Asterisks indicate significant differences between exposure and control groups (*P < 0.05,***P < 0.001; Dunn's test).
	Figure 10. Sagittal sections of immunohistochemically stained zebrafish (Danio rerio) pituitaries exposed to 0 and 50 mg/L PTU. The samples show clear proliferations of TSH-producing cells (▲) especially in the proximal pars distalis. Sections of 2 μm thickness immunostained with an anti-TSH antibody (nuclei were counterstained with Mayer's hematoxylin). PI—pars intermedia (adenohypophysis); PN—pars nervosa (neurohypophysis); PPD—proximal pars distalis (adenohypophysis); RPD—rostral pars distalis (adenohypophysis).
	Figure 11. TSH-producing cell counts of zebrafish (Danio rerio) pituitaries after exposure to 0 and 50 mg/L PTU. Statistical analysis was conducted on five immunostained sections, respectively (**P < 0.01; Mann-Whitney test).
	Figure 12. Representative histopathological alterations in hepatocytes of control (a) and PTU-exposed zebrafish (b). The well-visible glycogen deposits in the control ((a): ▲) are depleted in the higher concentration groups. Sections of 2 μm thickness stained with periodic acid-Schiff (PAS) and Mayer's hematoxylin.
	Figure 13. Representative ultrastructural alterations in hepatocytes of control (a) and PTU-exposed zebrafish (b). In the control fish, glycogen storage deposits are clearly visible ((a): ∗), whereas the exposed fish hardly display any glycogen in the cytoplasm. Moderate reductions and fenestrations of the rough endoplasmic reticulum are observable in PTU-exposed zebrafish ((b): ▲). Furthermore, the number of mitochondria is decreased. Magnification: 10,000x.

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