This exercise was designed to have students 1) observe a physiological color change in whole
organisms, and 2) correlate the color change (in vivo) with the responses occurring at the cellular
level (in vitro), especially in dermal melanophores. The color change process is relatively fast (30-
45 min) in killifish subjected to a black background, and the time course can be quantified using a
simple color index of 1 - 5. Dermal melanophores are very large and the degree of melanin
dispersion can be easily determined under the dissecting microscope (Hogben and Slome, 1931).
This pre-designed experiment was used as a pilot study prior to a subsequent series of studentdesigned
experiments with an emphasis on mechanisms of physiological color change in animals.