Agonistic Behaviour

Agonistic behaviour encompasses all behaviours related to social conflict, including threat displays, attacks, submission, and fleeing. In fish it includes: lateral displays (presenting the body broadside to appear larger), erection of spines and fins, operculum flaring, colour changes (darkening, brightening), charging, biting, and chasing. Most agonistic encounters are resolved by display without contact, minimising injury risk. Fish in established social hierarchies show stable dominance relationships with minimal agonistic behaviour. Agonistic behaviour intensifies in resource-limited conditions (food, mates, spawning sites) and has implications for aquaculture (aggression at high stocking density increases injury and stress).

Male Siamese fighting fish (Betta splendens) engage in highly ritualised lateral display — fanning all fins maximally to appear as large as possible — before escalating to physical combat if neither fish retreats.