Papers in the Biological Sciences


Date of this Version



Published in INVESTIGATIONS OF THE ICHTHYOFAUNA OF NICARAGUAN LAKES, ed. Thomas B. Thorson (University of Nebraska-Lincoln, 1976). Copyright © 1976 School of Life Sciences, University of Nebraska-Lincoln.


The Midas cichlid, Cichlasoma citrinellum, is a polychromatic fish that occurs in Nicaragua. All of these fish start life as normally colored, cryptic individuals. In some populations a few fish change into conspicuously colored morphs, most frequently gold. When kept in unmixed color groups, golds and normals grow at the same rate; but when they are mixed, growth of the golds becomes taster and that of the normals slower. Golds dominate normals in contests over food, which accounts for their advantage.