Coexistence of permanently territorial cichlids of the genus Petrochromis through male-mating attack

Abstract

Coexistence mechanisms of permanently territorial fishes proposed hitherto have been mainly based on interspecific competition. To test the hypothesis of the coexistence through male-mating aggression (Kohda, 1995a), spacing patterns of feeding territories of three coexisting herbivorous cichlids, Petrochromis polyodon, P. trewavasae and P. famula, were investigated in a homogeneous habitat at a shallow rocky shore in Lake Tanganyika. All three species maintained individual feeding territories that were defended against both conspecifics and congenerics and rarely overlapped either intra- or interspecifically. Territories of three species were scattered and covered almost all rocky bottoms. Territorial attacks usually occurred near the border of feeding territories. But male P. polyodon, the largest and socially most dominant fish, attacked conspecific males far beyond their feeding territories, which were widely separated. Removal of some territory owners suggested that such attacks result in the separate distribution of male P. polyodon territories. The interstitial space between P. polyodon feeding territories resulting from their mating aggression can be occupied by subordinate congeneric fishes. Male-mating attack of dominant males of Petrochromis will facilitate the coexistence of other congeners.