The angular orientation of the black eye-bar in Haplochromis burtoni (Cichlidae, Pisces) and its relevance to aggressivity

Summary

The effect of the black eye-bar in Haplochromis burtoni on the attack rate of conspecific males was found, using dummies, to depend on the angular orientation of this bar with respect to the body axis of the fish (Figs. 1, 4): The increment in attack rate increases as the black eye-bar parallels more closely the profile of the forehead and decreases as the bar approaches an orientation perpendicular to the forehead. This is valid independent of the actual body posture of the dummy bearing the black bar as could be shown by presenting dummies in a horizontal as well as in a head downward position. However, the head-down posture itself was found to cause an extra increment in attack rate, which may be considered to be additively or multiplicatively superimposed upon the increment determined by the orientation of the eye-bar with respect to the body axis (Fig. 4).