Fig. 6. Development of adult pigment patterns in D. rerio (A-F) and D. albolineatus (G-L). Panels shown are of selected days from a complete image series for individual, representative larvae. (A) In D. rerio, pigment pattern metamorphosis is marked by the differentiation of metamorphic melanophores (arrow, showing one of many) over the myotomes. The white box in each image delineates the horizontal myoseptum; the single arrowhead in A indicates one of several early larval melanophores that have persisted along the horizontal myoseptum through the beginning of metamorphosis. Double arrowhead indicates deep melanophores along the dorsal aspect of the neural tube; triple arrowhead, deep melanophores lining the dorsal surface of the peritoneum. sb, swim bladder. (B) As metamorphosis proceeds, additional metamorphic melanophores (small arrows) develop over the myotomes, and iridophores and xanthophores differentiate ventral to the horizontal myoseptum in the prospective primary interstripe region (large arrow). (C) By middle stages of pigment pattern metamorphosis, melanophores have started to organize into stripes in the region of the prospective dorsal primary melanophore stripe (p1D) and prospective ventral primary melanophore stripe (p1V). (D) As the dorsal and ventral melanophore stripes become increasingly distinctive, additional late metamorphic melanophores differentiate already within these stripes (e.g. arrow). (E) Near the completion of pigment pattern metamorphosis, distinctive dorsal and ventral primary melanophore stripes (1D, 1V) border a well-defined interstripe region. (F) Pigment pattern metamorphosis is completed with the development of scales and scale-associated melanophores (s). In D. albolineatus, melanophores typically do not persist along the horizontal myoseptum from earlier stages, and instead melanophores, initially deeper between the myotomes, migrate to the surface (arrowhead, data not shown). (H) Metamorphic melanophores (e.g. small arrow) differentiate widely scattered over the myotomes, as in D. rerio, but fewer iridophores (large arrow) develop ventral to the horizontal myoseptum. (I,J) As metamorphosis proceeds, additional metamorphic melanophores appear over the myotomes, yet these cells typically do not migrate far from their site of differentiation. Relatively few late metamorphic melanophores appear within the regions where stripes form in D. rerio (compare with D). (K) Near the completion of metamorphosis, melanophores remain relatively dispersed compared with D. rerio, and only a weak pattern of melanophore stripes (arrowheads) borders an irregular and narrow interstripe region on the posterior trunk. (L) At the end of metamorphosis, D. albolineatus have far fewer sub-dermal melanophores than D. rerio, and these cells are widely distributed where the interstripe region develops in D. rerio. The interstripe region extends only to the middle of the flank (arrow) and reddish erythrophores have started to differentiate within this region. Images shown have been rescaled across stages to maintain the same approximate field of view. Larval standard lengths in mm, (A-F) 7.1, 7.7, 8.3, 9.5, 12.0, 13.3, (G-L) 8.1, 9.3, 10.1, 11.0, 12.8, 13.4. Scale bars: in A, 500 µm for A,G; in F, 1 mm for F,L.