Sound Production by Cichlid Fishes.

Adults of three cichlid species, Hemichromis bimaculatus Gill, Cichlasoma nigrofasciatum (Gunther), and Pterophyllum sp., produce sounds of apparent biological significance. Both sexes of H. bimaculatus produce sounds, but whether both sexes in the other species produce sounds has not been established. The most intense tone frequencies in H. bimaculatus and C. nigrofasciatum lie generally between 300 and 500 cycles per second. The sound produced by Pterophyllum sp., however, has a broad maximum intensity around 3500 cycles per second and component frequencies over 10,000 cycles per second. Sound production appears to depend on the aggressiveness of the individual.