On the function of the 'eye-spots' in agonistic behaviour in the fire-mouth cichlid (Cichlasoma Meeki)

During frontal threatening, individuals of the fire-mouth cichlid (Cichlasoma meeki) dilate their opercula, thereby demonstrating two conspicous 'eye-spots'. In a hostile situation, a fish confronted with an opponent whose eye-spots have been experimentally removed is more likely to react with overt aggression towards the other. Fights also follow a more violent course than does a 'normal' fight between two intact males. A tentative explanation to these results is advanced which supposes that the eye-spots may exert an 'intimidating' effect upon the opponent during threat and fighting. This hypothesis is also supported by an experiment where males were confronted with a mirror. In this situation the distance between the mirror and the fish during frontal threat was significantly shorter in fishes lacking eye-spots, indicating that the intimidating effect emerging from the mirror image was diminished. In a third set of experiments when two males (one intact and one without eye-spots) competed for the only suitable territory site in an aquarium, the intact male eventually dominated the other in five of six aquariums.