Abstract
The melanophores and xanthophores of Pseudopleuronectes americanus display different adaptive capacities to a white background under continuous (1 week) illumination compared with an equivalent period under diurnal, alternating light (12 h) and dark (12 h) photoperiods. Under the repeated diurnal photocycles on white, melanosomes partly disperse during dark photoperiods, but there is cumulative melanosome aggregation during successive light photoperiods that is interpreted as a slow physiological summation. Consequently, there is no significant difference in the final degree of aggregation attained on a white background on completion of either illumination protocol. In contrast, xanthosomes attain a high degree of aggregation during white background adaptation under continuous illumination, but do not display slow "summation" of pigment aggregation in response to the diurnal light photoperiods. The differences between melanosome and xanthosome aggregation under these photoperiod regimes are discussed in relation to the previously established types of balance between neural and humoral systems controlling flounder melanophores and xanthophores.
Published Version
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