Deployment of Sudan Black-stained granulocytes from embryo to juvenile zebrafish. (A) 48 hpf embryo. (i) Lateral view of the head; the granulocytes are mainly dispersed in the mesenchyme; granulocytes in the yolk sac (ii), head epidermis (iii) and mesenchyme (iv); (v) Lateral view of the tail, where larval hematopoiesis is beginning. (B) 4 dpf larvae, head region. Ventrolateral (i) and ventral (ii) views, showing the increasing number of granulocytes. Examples of granulocytes between 2 cephalic muscle fibers (iii), in the mesenchyme (iv), in the epidermis (note the characteristic actin ridges of the overlying periderm in the lower half of the image) (v), and at the border of a neuromast (vi). (C) 7 dpf larvae. (i) Granulocytes gathered around the pronephric glomerulus (arrow), revealing the beginning of definitive granulopoiesis in the kidney. Granulocytes along the basal lamina of the gut (ii) and the left pronephric duct (iii); (iv) lateral view of the tail showing the growing granulocyte population in the CHT, the site of larval hematopoiesis. (D) 14 dpf larvae. Ventral (i) and dorsal (ii) views of the anterior region; note the paucity of granulocytes in the dorsal head, except most anteriorly around the olfactory pits, and the increasing number of granulocytes in the kidney around the glomerulus (arrow), also visible in lateral view in (iii). (E) 30 dpf juvenile fish. (i) The head kidney (remnant of the pronephros) is now full of granulocytes (arrow). Granulocyte populations in the caudal fin (ii), all over the head (iii), in the gills (iv), in the left olfactory pit (v), and in the head kidney (vi) (left lateral side). e indicates inner ear; ca, caudal artery; g, pronephric glomerulus; k, kidney; m, muscle fiber; op, olfactory pit; pd, pronephric duct; and r, retina. (Scale bars, 10 μm in Ab-d, Bc-f; 20 μm in Cb,c; 100 μm in Aa, Ba,b, Ca, Eb-f.)