Receptor mechanisms in fish chromatophores--V. MSH disperses melanosomes in both dermal and epidermal melanophores of a catfish (Parasilurus asotus).

1. Synthetic alpha-MSH was tested for its action on dermal and epidermal melanophores of the siluroid catfish. Parasilurus asotus. 2. MSH did not produce melanosome aggregation in these melanophores. 3. It was, however, very effective in bringing about pigment dispersion in dermal melanophores. 4. Epidermal melanophores were also responsive to MSH, although the rate and the degree of the response was smaller than those of the dermal melanophores. 5. A possible role of MSH in skin color changes in vivo is discussed.