RESUMO
The striped pigment patterns in the flanks of zebrafish result from chromatophores deep within the dermis or hypodermis, while superficial melanophores associated with dermal scales add a dark tint to the dorsal coloration. The responses of these chromatophores were compared during the long-term adaptation of zebrafish to a white or a black background. In superficial skin, melanophores, xanthophores, and two types of iridophores are distributed in a gradient along the dorso-ventral axis independent of the hypodermal pigment patterns. Within one week the superficial melanophores and iridophores changed their density and/or areas of distribution, which adopted the dorsal skin color and the hue of the flank to the background, but did not affect the striped pattern. The increases or decreases in superficial melanophores are thought to be caused by apoptosis or by differentiation, respectively. When the adaptation period was prolonged for more than several months, the striped color pattern was also affected by changes in the width of the black stripes. Some black stripes disappeared and interstripe areas were emphasized with a yellow color within one year on a white background. Such long-term alteration in the pigment pattern was caused by a decrease in the distribution of melanophores and a concomitant increase in xanthophores in the hypodermis. These results indicate that morphological responses of superficial chromatophores contribute to the effective and rapid background adaptation of dorsal skin and while prolonged adaptation also affects hypodermal chromatophores in the flank to alter the striped pigment patterns.
