Here is an article from my web page about the social dynamic of my tank (please bear in mind that I didn't write it for an expert audience such as yourselves):
The fishy social dynamic of violence:
This aquarium mainly houses fish from the Amazon River and other American freshwater systems
These types of fish are large, colourful and hardy. In my experience they are also violent, territorial and predatory! You can't blame them really, in their native waters they have to live with piranhas and giant parisites! I'd be angry too!
Keeping groups of these types of fish always leads to aggression and bullying problems. Fish are often injured and stressed. Sometimes fish are murdered by their tank mates!
To reduce this problem I drew on the knowledge of people who breed very aggressive Australian grunters. From their ideas I developed a plan to regulate the social dynamic of my tank:
The biggest fish is non-violent
The Giant Gourami is far larger than any other fish in this tank, yet it is fairly placid. The other fish like to eat each other, but the Giant Gourami prefers to munch on bananna and broccoli. Because he is much bigger than the other fish he prevents any of them assuming the dominant position. This tank has a benevolant leader.
The angry fish are kept in groups
1 angry fish will attack other fish.
2 angry fish of the same species will fight each other until one dies and then the survivor will attack other fish.
4 or more angry fish of the same species will try to fight with each other, fail (because there are too many to fight) and leave other fish alone. They must also watch their own butt all the time in case they are attacked by one of their own.
In my experience this system works without fail to reduce violence. I keep all my nasties in groups of 4 or more. If violence persists then I just increase numbers.
Fish that are stupid, fast and tough make great targets for aggression
Target fish are used to keep the nasties from thinking about bullying each other over territory.
I love stupid fish, and they don't come much dumber than cypranids (like goldfish, carp and tinfoil barbs). My 3 big tinfoil barbs are glorified beautiful idiots. No matter how many times they swim into another fish's territory and get attacked they never learn. Fortunately they are also fast and tough so when they are attacked they can survive the chomp and escape quickly (to do it all over again).
The big nasties find the tinfoil barbs so annoying that they become distracted from fighting with each other. It makes it difficult for a territory to be formed when it is never respected no matter how hard it is defended!
The proof is in the pudding - evil is tamed
When I have guests come over they have no idea about the nature of the fish in my tank. They comment on how tranquil the aquarium is. I particularly enjoy the look of shock on their faces at feeding time
