Studies on the color-change mechanism in a fresh-water teleost, Nandus nandus (Ham.). II. Hormonal control.

The chromatic spinal sectioning (mostly at 3rd, 3/4th and 4th vertebral levels) produced the maximal darkening in the fish. This darkening persisted in the fish on a black background, but a slow and gradual paling occurred in the operated animals when placed over a white background. These animals reached the maximum paling in 168 h as compared to the unoperated ones where similar state of paling was attained in a comparatively shorter period (3 to 5 h). The distinct difference in the results in respect of the rates of paling in the operated (melanophores under hormonal control only) and unoperated animals clearly suggests the involvement of a pituitary-borne melanophore-aggregating hormone (MAH) in the chromatic control mechanism of the fish Nandus nandus.