Encontros agonísticos e territorialidade entre machos de híbrido vermelho de tilápia, Oreochromis niloticus (Linnaeus, 1758) x Oreochromis mossambicus (Peters, 1852) e de tilápia do Nilo, Oreochromis niloticus (Cichlidae)

Hybrid red tilapia, Oreochromis niloticus (Linnaeus, 1758) x Oreochromis mossambicus (Peters, 1852) is a territorial fish and is aggressive towards conspecifics during the reproductive phase. This paper registers the levels of aggression and dominance between these males, the effect of territorialownership on the outcome of competitions and behaviour related to nest construction. The observations were carried out during August, 2003 to June, 2004. The results show that aggression of hybrid red tilapia males towards males of Nile tilapia was higher than the reverse. The difference in body size determines dominance in both. The males of resident hybridred tilapia were more aggressive than the males of resident Nile tilapia. The non-resident Nile tilapia were more aggressive than the males of non-resident hybrid red tilapia. The aggression presented by the males of hybrid red tilapia and Nile tilapia in their own territory was higher than in neutral situation. The nest construction by males both species wasindependent of the presence of females