Aggressive behaviour and dominance relationships of the dark chub,Zacco temmincki with special reference to their individual recognition

Aggressive behaviour and dominance relationships ofZacco temmincki were observed by introducing fish into an enclosed pond. Chase (-flee), lateral display, parallel swim and butt were the principal behavioural patterns in aggressive encounters between fish, while chase, resulting in lateral display by the chased fish was the most common behavioural sequence. Initially, mutual behavioural patterns such as parallel swim and mutual lateral display were most evident among the total aggressive acts although chase became dominant three days after introduction into the pond. The dominance matrix constructed from chase-flee interactions during all observation periods contained many reverse attacks (336 out of 2,740 chases). These reverse attacks did not concentrate upon a specific period and were not site-dependent. Examination of chase-flee interactions and the subsequent behavioural pattern revealed that a chased fish reacted to the chaser either by attacking in turn, or performing lateral display etc. roughly in relation to the dominance rank of the chaser. This result implies that fish recognized each other to a great extent during aggressive encounters. It seems likely that such individual recognition was initiated during the early period when mutual behaviour was most frequent, and that some attacks against the dominance order were caused as a result of revolts rather than mistakes.