During the social encounter, the dorsal fins of both fish were raised and both swam towards each other indicating their preparedness to fight. Then they begun aggressive interaction which involved chasing, rapid circling and biting directed against the mouth, fins and all other body parts of the opponent. During this period of intensive interaction, both fish exhibited pale body stripe coloration. However, during the later part of the interaction, challenged fish mostly rebuffed attacks and at this period, one of the fish chased and bit the flanks of the other fish that was fleeing. At this point, aggressive behaviour becomes unidirectional, and an aggressive dominant individual and a retreating subordinate fish were clearly identified. It was also observed that subordination increased the body- and eye-darkening color of the fish while dominance decreased it.
In the current study, the observed changes in behavior and body and eye colors of the competing fish served as social signals to the opponents to limit aggressive interaction. When social hierarchy had been established, subordination increased the body stripes and eye-darkening patterns of the fish while dominance decreased it.
WOW...Thanks for the providing this site, a lot of really detail information. But none of my fish has ever shown sighs of aggression or even males chasing females. This condition as been going on for about 2 months with no death occurring. The darkness doesn't seem to appear in strips more like dark spots tightly group together forming a darker underside fading way as it moves to the top of the fish.
I imagine they react similarly to any severe "stress"... you would have to figure out what's causing the stress; oxygen, light, temperature, some predator (or perceived predator like the neighbor kids chasing them around the tank), or maybe some imbalance in the water quality parameters.