Comparative aggression and dominance of Oreochromis niloticus (Linnaeus, 1758) and Oreochromis mortimeri (Trewavas, 1966) from paired contest in aquaria
文摘
Oreochromis niloticus was introduced in Lake Kariba, and it displaced the endemic Oreochromis mortimeri from many areas of the lake. Studying the interaction between the two species sheds light on the nature of the displacement process. The levels of aggression within and between the two species and the effect of relative size were studied in the laboratory. O. mortimeri attacked O. niloticus first in most of the encounters whether it was the bigger or smaller of the pair. In encounters where O. niloticus was smaller, 2 (8.3%) O. niloticus made the first bite and 8 (40.0%) made the first bite when O. niloticus was the bigger of the pair. Over a 30-min encounter, O. mortimeri was dominant and delivered significantly more bites (7.79 ± 2.31 bites) than O. niloticus (4.53 ± 1.53 bites) (P = 0.03, t = 2.18). Unlike O. mortimeri, O. niloticus attacked first only when it was considerably bigger than the opponent. The association of large body size with higher aggression may mean that O. niloticus, which grows faster and larger than O. mortimeri, has size advantage. Therefore, interaction between the two species may be complex, and aggression may be just one of the factors that affect the interaction of these fish species.