Factors influencing pairbond stability in convict cichlids (Cichlasoma nigrofasciatum)

In isolated pairs of the biparental convict cichlid (Cichlasoma nigrofasciatum) caring for fry, pairbonds can be broken by removal of the fry. Within three hours, the mates of many pairs become so mutually aggressive that the female finally flees from her larger mate, who chases her. The pairbond is mended within seconds upon re-introduction of the fry. Yet removal of young leaves some pairs little or not at all affected. They seem to have more stable pairbonds. Multiple regression of data from 39 pairs on a quantitative measure of pairbond destruction revealed support for the so-called parity-hypothesis, which holds that a cichlid pair is compatible only when the female's aggressiveness compensates for her smaller size. The size of the female relative to the male's, and her aggressiveness relative to his in the undisturbed situation, proved positive predictors of pair stability in the fry stage. Thus the same factors which have earlier been shown to favour pair formation in other biparental cichlids seem also responsible for pair stability in a later stage of the reproductive cycle.