Is this a serious question? Inherently Bichirs are not an overly aggressive species, not on the line of snakeheads or certain cichlids. That said they are predatory and can be quite effective at that.
If you are looking to build up a collection of polypterus it is better to minimize aggression, eg not feeding live foods. Makes it much easier to introduce new fish.(Adding a 10" fish into a tank with a 20"+ fish)
Now if by aggression you mean activity level, that is a whole other thing. At any rate, good luck with your fish and enjoy it however it turns out.