Skeletal anatomy of the zebrafish pectoral fin. a Skeletal anatomy of the zebrafish pectoral fin with Alizarin Red staining. The bottom box shows a magnified view of the upper whole pectoral fin skeleton in the inset. The scale bar indicates 1 mm. b, c Schematics of the fin rays and radials. Drawings in dark blue and pink indicate radials and fin rays, respectively. Each of the proximal radials (pr) and distal radials (dr) are indicated in c. dr5, and dr8 occasionally did not appear (asterisk)

Observation of skeletal anatomy of the pectoral fin in the RW strain. a Distribution of the variation in fin ray number. b Relationship between the number of rays and body length. Blue circles indicate individuals. c Ratio of the combination of the numbers of fin rays in the left and right pectoral fins. d. Schematic drawing of the connection between the fin rays (red bar with circle) and distal radials (dark blue). Light blue, orange, and green boxes indicate the relationship in the one-to-one, one-to-one or two, and one-to-three or more modes, respectively. d’. Connection between fin rays and the sixth and seventh radials. The seventh radial showed connection in a one-to-two mode; the sixth radial showed the connection in a one-to-two (left panel) or a one-to-one (right panel) mode. d”. Connection between the fin rays and the eighth radial. The number of fin rays connected to the eighth radial varied (four rays in the left panel and three rays in the right panel). Blue-colored arrowheads with dr5–8 indicate the 5th to 8th distal radials, respectively. Blue-outlined arrowheads with dr5 in the right panel of d’ and dr8 in the right panel of d” indicate the absence of the 5th and 8th distal radials, respectively. Black-colored numbers indicate fin ray numbers. Underlined characters in d’ indicate the 6th and 7th distal radials and the fin rays connected to them. Underlined characters in d” indicate the 8th distal radial and the fin rays connected to it

Process of morphogenesis of the fin rays and radials. Calcified bones (Alizarin Red) and chondrogenic cells (col2a:EGFP) of the left pectoral fin in individual tracing specimens were observed at 28 dpf (a), 32 dpf (b), 36 dpf (c), and 40 dpf (d). The observed fish were crossbred. Orange arrowheads with numbers indicate the most posterior fin ray. White arrowheads with dr3–7 indicate newly appearing distal radials. The scale bar in a indicates 200 μm. CSZ, cartilage subdivision zone. sc, anlagen of the scapula. The asterisk in a indicates the reflected signal of the iridophore on the swim bladder

Expression pattern of EGFP in the pectoral fin of gt1641A and gt223A transgenic zebrafish. a-e’. Expression pattern of EGFP in the pectoral fin of a gt1641A transgenic fish observed at 1 dpf (a), 1 wpf (b), 2 wpf (c), 3 wpf (d), and 4 wpf (e, e’). f-j’. Expression pattern of EGFP in the pectoral fin of a gt223A transgenic fish observed at 2 dpf (f), 1 wpf (g), 2 wpf (h), 3 wpf (i), and 4 wpf (j, j’). White dashed lines indicate outline of the fin fold in the pectoral fin. Arrows in d indicate depletion of EGFP expression. Magenta in e’ and j’ indicate calcified bones stained by Alizarin Red. Scale bars in a and b and those in c, d, e, and h indicate 75 μm and 250 μm, respectively