Table 2.

Semiquantitative evaluation of alterations in the thyroid of zebrafish (Danio rerio) induced by PTU.

PTU (mg/L)	Control	2.5	10	25	50
Follicles
Total number		+	++	+++	+++
Size		+	+	+++	+++
Shape			++	+++	++++
Blood vessels
Hyperemia			++	+++	++++
Colloid
Reduced homogeneity			+	+++	++
Reduced density			+	+++	++
Colloid depletion	+	+	+	+	+
Foamy texture				+	+
Cellular inclusions				++	++
Epithelial cells
Cell height			++	+++	+++
Stratification				++	+++
Cell crowding			+	++	+++

Data are given as means of observation in 20 individuals per exposure group: ⁺little developed; ⁺⁺moderately developed; ⁺⁺⁺strongly developed; ⁺⁺⁺⁺very strongly developed.