Current status:
The two bigger ones have claimed different sides of the tank – one stays on the left side in a shelter, the other on the right side under a leaf. Both show the same dark fin colouration and tail pattern now.
Both attack and chase the two smaller ones if they come too near to the right or left side. Both big ones only watch each other, they don’t swim into the other’s territory, and they don’t chase each other. Watching each other, they stand in a head-down angle on opposite sides, their colours turning dark.
This is what the two bigger ones look like now – the biggest being a bit darker than the other one:
No iridescent colour bands – but still very dark for a female. Connected with the behaviour reported above I have a question: Do paro females show territorial behaviour? Do they claim territories and defend them?
This is how the two smaller ones look like:
The different body colouration is no artefact – the bigger ones are golden and black, the smaller ones silvery and black.