Abstract An experimental model was constructed using seven postulates derived from the experimental results of Zayan (1974, 1975a,b,c, 1976). The model specifies the relative importance of several asymmetries in predicting aggressive dominance in Xiphophorus helleri . These asymmetries concern difference between duellists with respect to: prior residence in the tested area (vs intrusion); immediate social experiences of dominance or submission; social isolation; individual familiarity and recognition. The predictions of the general model were checked experimentally and confirmed; a multiple orthogonal regression accounted for about 97% of the variance in our experimental results. The basic experimental results serving as postulates were confirmed and could be generalized; a new synthetic and predictive model was formulated concerning the determinants of aggressive dominance in Xiphophorus .