Morphological color changes in the medaka, Oryzias latipes, after prolonged background adaptation—I. Changes in the population and morphology of melanophores

Abstract 1. 1. Actaptation to a black or a white background for 10 days induced an apparent increase or decrease, respectively, in the integumentary pigmentation of the medaka, Oryzias latipes (wild type). 2. 2. In the fish adapted to a black background, both the number and the size of melanophores on the scales isolated from the head and dorsal trunk were found to have increased, while only their number increased on the scales from the lateral part of the trunk. 3. 3. Conversely, dopa-positive melanoblasts were more densely detected in the fish adapted to a white background than in black-adapted fish. 4. 4. In chemically sympathectomized fish, melanophores of the black-adapted fish were larger than those of the white-adapted fish, although there was no difference in terms of the number of pigment cells. 5. 5. These results indicate that, during the background adaptation, neural processes have some effects on the number of melanophores.